1 /*
2 * Copyright (c) 2008, 2020, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.JavaLangAccess;
29 import jdk.internal.access.SharedSecrets;
30 import jdk.internal.misc.VM;
31 import jdk.internal.module.IllegalAccessLogger;
32 import jdk.internal.org.objectweb.asm.ClassReader;
33 import jdk.internal.org.objectweb.asm.Opcodes;
34 import jdk.internal.reflect.CallerSensitive;
35 import jdk.internal.reflect.Reflection;
36 import jdk.internal.vm.annotation.ForceInline;
37 import sun.invoke.util.ValueConversions;
38 import sun.invoke.util.VerifyAccess;
39 import sun.invoke.util.Wrapper;
40 import sun.reflect.misc.ReflectUtil;
41 import sun.security.util.SecurityConstants;
42
43 import java.lang.invoke.LambdaForm.BasicType;
44 import java.lang.reflect.Constructor;
45 import java.lang.reflect.Field;
46 import java.lang.reflect.Member;
47 import java.lang.reflect.Method;
48 import java.lang.reflect.Modifier;
49 import java.lang.reflect.ReflectPermission;
50 import java.nio.ByteOrder;
51 import java.security.ProtectionDomain;
52 import java.util.ArrayList;
53 import java.util.Arrays;
54 import java.util.BitSet;
55 import java.util.Iterator;
56 import java.util.List;
57 import java.util.Objects;
58 import java.util.Set;
59 import java.util.concurrent.ConcurrentHashMap;
60 import java.util.stream.Collectors;
61 import java.util.stream.Stream;
62
63 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
64 import static java.lang.invoke.MethodHandleNatives.Constants.*;
65 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
66 import static java.lang.invoke.MethodType.methodType;
67
68 /**
69 * This class consists exclusively of static methods that operate on or return
70 * method handles. They fall into several categories:
71 * <ul>
72 * <li>Lookup methods which help create method handles for methods and fields.
73 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
74 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
75 * </ul>
76 * A lookup, combinator, or factory method will fail and throw an
77 * {@code IllegalArgumentException} if the created method handle's type
78 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
79 *
80 * @author John Rose, JSR 292 EG
81 * @since 1.7
82 */
83 public class MethodHandles {
84
85 private MethodHandles() { } // do not instantiate
86
87 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
88
89 // See IMPL_LOOKUP below.
90
91 //// Method handle creation from ordinary methods.
92
93 /**
94 * Returns a {@link Lookup lookup object} with
95 * full capabilities to emulate all supported bytecode behaviors of the caller.
96 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
97 * Factory methods on the lookup object can create
98 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
99 * for any member that the caller has access to via bytecodes,
100 * including protected and private fields and methods.
101 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
102 * Do not store it in place where untrusted code can access it.
103 * <p>
104 * This method is caller sensitive, which means that it may return different
105 * values to different callers.
106 * @return a lookup object for the caller of this method, with
107 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
108 */
109 @CallerSensitive
110 @ForceInline // to ensure Reflection.getCallerClass optimization
111 public static Lookup lookup() {
112 return new Lookup(Reflection.getCallerClass());
113 }
114
115 /**
116 * This reflected$lookup method is the alternate implementation of
117 * the lookup method when being invoked by reflection.
118 */
119 @CallerSensitive
120 private static Lookup reflected$lookup() {
121 Class<?> caller = Reflection.getCallerClass();
122 if (caller.getClassLoader() == null) {
123 throw newIllegalArgumentException("illegal lookupClass: "+caller);
124 }
125 return new Lookup(caller);
126 }
127
128 /**
129 * Returns a {@link Lookup lookup object} which is trusted minimally.
130 * The lookup has the {@code UNCONDITIONAL} mode.
131 * It can only be used to create method handles to public members of
132 * public classes in packages that are exported unconditionally.
133 * <p>
134 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
135 * of this lookup object will be {@link java.lang.Object}.
136 *
137 * @apiNote The use of Object is conventional, and because the lookup modes are
138 * limited, there is no special access provided to the internals of Object, its package
139 * or its module. This public lookup object or other lookup object with
140 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
141 * is not used to determine the lookup context.
142 *
143 * <p style="font-size:smaller;">
144 * <em>Discussion:</em>
145 * The lookup class can be changed to any other class {@code C} using an expression of the form
146 * {@link Lookup#in publicLookup().in(C.class)}.
147 * A public lookup object is always subject to
148 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
149 * Also, it cannot access
150 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
151 * @return a lookup object which is trusted minimally
152 *
153 * @revised 9
154 * @spec JPMS
155 */
156 public static Lookup publicLookup() {
157 return Lookup.PUBLIC_LOOKUP;
158 }
159
160 /**
161 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
162 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
163 * The returned lookup object can provide access to classes in modules and packages,
164 * and members of those classes, outside the normal rules of Java access control,
165 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
166 * <p>
167 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
168 * allowed to do deep reflection on module {@code M2} and package of the target class
169 * if and only if all of the following conditions are {@code true}:
170 * <ul>
171 * <li>If there is a security manager, its {@code checkPermission} method is
172 * called to check {@code ReflectPermission("suppressAccessChecks")} and
173 * that must return normally.
174 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
175 * full privilege access}. Specifically:
176 * <ul>
177 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
178 * (This is because otherwise there would be no way to ensure the original lookup
179 * creator was a member of any particular module, and so any subsequent checks
180 * for readability and qualified exports would become ineffective.)
181 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
182 * (This is because an application intending to share intra-module access
183 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
184 * deep reflection to its own module.)
185 * </ul>
186 * <li>The target class must be a proper class, not a primitive or array class.
187 * (Thus, {@code M2} is well-defined.)
188 * <li>If the caller module {@code M1} differs from
189 * the target module {@code M2} then both of the following must be true:
190 * <ul>
191 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
192 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
193 * containing the target class to at least {@code M1}.</li>
194 * </ul>
195 * </ul>
196 * <p>
197 * If any of the above checks is violated, this method fails with an
198 * exception.
199 * <p>
200 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
201 * returns a {@code Lookup} on {@code targetClass} with
202 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} and
203 * {@code null} previous lookup class.
204 * <p>
205 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
206 * returns a {@code Lookup} on {@code targetClass} that records
207 * the lookup class of the caller as the new previous lookup class and
208 * drops {@code MODULE} access from the full privilege access.
209 *
210 * @param targetClass the target class
211 * @param caller the caller lookup object
212 * @return a lookup object for the target class, with private access
213 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
214 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
215 * @throws SecurityException if denied by the security manager
216 * @throws IllegalAccessException if any of the other access checks specified above fails
217 * @since 9
218 * @spec JPMS
219 * @see Lookup#dropLookupMode
220 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
221 */
222 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
223 if (caller.allowedModes == Lookup.TRUSTED) {
224 return new Lookup(targetClass);
225 }
226
227 SecurityManager sm = System.getSecurityManager();
228 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
229 if (targetClass.isPrimitive())
230 throw new IllegalArgumentException(targetClass + " is a primitive class");
231 if (targetClass.isArray())
232 throw new IllegalArgumentException(targetClass + " is an array class");
233 // Ensure that we can reason accurately about private and module access.
234 if (!caller.hasFullPrivilegeAccess())
235 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
236
237 // previous lookup class is never set if it has MODULE access
238 assert caller.previousLookupClass() == null;
239
240 Class<?> callerClass = caller.lookupClass();
241 Module callerModule = callerClass.getModule(); // M1
242 Module targetModule = targetClass.getModule(); // M2
243 Class<?> newPreviousClass = null;
244 int newModes = Lookup.FULL_POWER_MODES;
245
246 if (targetModule != callerModule) {
247 if (!callerModule.canRead(targetModule))
248 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
249 if (targetModule.isNamed()) {
250 String pn = targetClass.getPackageName();
251 assert !pn.isEmpty() : "unnamed package cannot be in named module";
252 if (!targetModule.isOpen(pn, callerModule))
253 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
254 }
255
256 // M2 != M1, set previous lookup class to M1 and drop MODULE access
257 newPreviousClass = callerClass;
258 newModes &= ~Lookup.MODULE;
259 }
260
261 if (!callerModule.isNamed() && targetModule.isNamed()) {
262 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
263 if (logger != null) {
264 logger.logIfOpenedForIllegalAccess(caller, targetClass);
265 }
266 }
267 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
268 }
269
270 /**
271 * Returns the <em>class data</em> associated with the lookup class
272 * of the specified {@code Lookup} object, or {@code null}.
273 *
274 * <p> Classes can be created with class data by calling
275 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, Lookup.ClassOption...)
276 * Lookup::defineHiddenClassWithClassData}.
277 * A hidden class with a class data behaves as if the hidden class
278 * has a private static final unnamed field pre-initialized with
279 * the class data and this method is equivalent as if calling
280 * {@link ConstantBootstraps#getStaticFinal(Lookup, String, Class)} to
281 * obtain the value of such field corresponding to the class data.
282 *
283 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
284 * must have {@link Lookup#ORIGINAL ORIGINAL} access in order to retrieve
285 * the class data.
286 *
287 * @apiNote
288 * This method can be called as a bootstrap method for a dynamically computed
289 * constant. A framework can create a hidden class with class data, for
290 * example that can be {@code List.of(o1, o2, o3....)} containing more than
291 * one live object. The class data is accessible only to the lookup object
292 * created by the original caller but inaccessible to other members
293 * in the same nest. If a framework passes security sensitive live objects
294 * to a hidden class via class data, it is recommended to load the value
295 * of class data as a dynamically computed constant instead of storing
296 * the live objects in private fields which are accessible to other
297 * nestmates.
298 *
299 * @param <T> the type to cast the class data object to
300 * @param caller the lookup context describing the class performing the
301 * operation (normally stacked by the JVM)
302 * @param name ignored
303 * @param type the type of the class data
304 * @return the value of the class data if present in the lookup class;
305 * otherwise {@code null}
306 * @throws IllegalAccessException if the lookup context does not have
307 * original caller access
308 * @throws ClassCastException if the class data cannot be converted to
309 * the specified {@code type}
310 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, Lookup.ClassOption...)
311 * @since 15
312 */
313 static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
314 if (!caller.hasFullPrivilegeAccess()) {
315 throw new IllegalAccessException(caller + " does not have full privilege access");
316 }
317 Object classData = MethodHandleNatives.classData(caller.lookupClass);
318 return type.cast(classData);
319 }
320
321 /**
322 * Performs an unchecked "crack" of a
323 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
324 * The result is as if the user had obtained a lookup object capable enough
325 * to crack the target method handle, called
326 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
327 * on the target to obtain its symbolic reference, and then called
328 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
329 * to resolve the symbolic reference to a member.
330 * <p>
331 * If there is a security manager, its {@code checkPermission} method
332 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
333 * @param <T> the desired type of the result, either {@link Member} or a subtype
334 * @param target a direct method handle to crack into symbolic reference components
335 * @param expected a class object representing the desired result type {@code T}
336 * @return a reference to the method, constructor, or field object
337 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
338 * @throws NullPointerException if either argument is {@code null}
339 * @throws IllegalArgumentException if the target is not a direct method handle
340 * @throws ClassCastException if the member is not of the expected type
341 * @since 1.8
342 */
343 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
344 SecurityManager smgr = System.getSecurityManager();
345 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
346 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
347 return lookup.revealDirect(target).reflectAs(expected, lookup);
348 }
349 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
350 private static final java.security.Permission ACCESS_PERMISSION =
351 new ReflectPermission("suppressAccessChecks");
352
353 /**
354 * A <em>lookup object</em> is a factory for creating method handles,
355 * when the creation requires access checking.
356 * Method handles do not perform
357 * access checks when they are called, but rather when they are created.
358 * Therefore, method handle access
359 * restrictions must be enforced when a method handle is created.
360 * The caller class against which those restrictions are enforced
361 * is known as the {@linkplain #lookupClass() lookup class}.
362 * <p>
363 * A lookup class which needs to create method handles will call
364 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
365 * When the {@code Lookup} factory object is created, the identity of the lookup class is
366 * determined, and securely stored in the {@code Lookup} object.
367 * The lookup class (or its delegates) may then use factory methods
368 * on the {@code Lookup} object to create method handles for access-checked members.
369 * This includes all methods, constructors, and fields which are allowed to the lookup class,
370 * even private ones.
371 *
372 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
373 * The factory methods on a {@code Lookup} object correspond to all major
374 * use cases for methods, constructors, and fields.
375 * Each method handle created by a factory method is the functional
376 * equivalent of a particular <em>bytecode behavior</em>.
377 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
378 * the Java Virtual Machine Specification.)
379 * Here is a summary of the correspondence between these factory methods and
380 * the behavior of the resulting method handles:
381 * <table class="striped">
382 * <caption style="display:none">lookup method behaviors</caption>
383 * <thead>
384 * <tr>
385 * <th scope="col"><a id="equiv"></a>lookup expression</th>
386 * <th scope="col">member</th>
387 * <th scope="col">bytecode behavior</th>
388 * </tr>
389 * </thead>
390 * <tbody>
391 * <tr>
392 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
393 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
394 * </tr>
395 * <tr>
396 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
397 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
398 * </tr>
399 * <tr>
400 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
401 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
402 * </tr>
403 * <tr>
404 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
405 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
406 * </tr>
407 * <tr>
408 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
409 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
410 * </tr>
411 * <tr>
412 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
413 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
414 * </tr>
415 * <tr>
416 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
417 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
418 * </tr>
419 * <tr>
420 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
421 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
422 * </tr>
423 * <tr>
424 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
425 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
426 * </tr>
427 * <tr>
428 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
429 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
430 * </tr>
431 * <tr>
432 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
433 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
434 * </tr>
435 * <tr>
436 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
437 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
438 * </tr>
439 * <tr>
440 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
441 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
442 * </tr>
443 * <tr>
444 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
445 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
446 * </tr>
447 * </tbody>
448 * </table>
449 *
450 * Here, the type {@code C} is the class or interface being searched for a member,
451 * documented as a parameter named {@code refc} in the lookup methods.
452 * The method type {@code MT} is composed from the return type {@code T}
453 * and the sequence of argument types {@code A*}.
454 * The constructor also has a sequence of argument types {@code A*} and
455 * is deemed to return the newly-created object of type {@code C}.
456 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
457 * The formal parameter {@code this} stands for the self-reference of type {@code C};
458 * if it is present, it is always the leading argument to the method handle invocation.
459 * (In the case of some {@code protected} members, {@code this} may be
460 * restricted in type to the lookup class; see below.)
461 * The name {@code arg} stands for all the other method handle arguments.
462 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
463 * stands for a null reference if the accessed method or field is static,
464 * and {@code this} otherwise.
465 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
466 * for reflective objects corresponding to the given members declared in type {@code C}.
467 * <p>
468 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
469 * as if by {@code ldc CONSTANT_Class}.
470 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
471 * <p>
472 * In cases where the given member is of variable arity (i.e., a method or constructor)
473 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
474 * In all other cases, the returned method handle will be of fixed arity.
475 * <p style="font-size:smaller;">
476 * <em>Discussion:</em>
477 * The equivalence between looked-up method handles and underlying
478 * class members and bytecode behaviors
479 * can break down in a few ways:
480 * <ul style="font-size:smaller;">
481 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
482 * the lookup can still succeed, even when there is no equivalent
483 * Java expression or bytecoded constant.
484 * <li>Likewise, if {@code T} or {@code MT}
485 * is not symbolically accessible from the lookup class's loader,
486 * the lookup can still succeed.
487 * For example, lookups for {@code MethodHandle.invokeExact} and
488 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
489 * <li>If there is a security manager installed, it can forbid the lookup
490 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
491 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
492 * constant is not subject to security manager checks.
493 * <li>If the looked-up method has a
494 * <a href="MethodHandle.html#maxarity">very large arity</a>,
495 * the method handle creation may fail with an
496 * {@code IllegalArgumentException}, due to the method handle type having
497 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
498 * </ul>
499 *
500 * <h2><a id="access"></a>Access checking</h2>
501 * Access checks are applied in the factory methods of {@code Lookup},
502 * when a method handle is created.
503 * This is a key difference from the Core Reflection API, since
504 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
505 * performs access checking against every caller, on every call.
506 * <p>
507 * All access checks start from a {@code Lookup} object, which
508 * compares its recorded lookup class against all requests to
509 * create method handles.
510 * A single {@code Lookup} object can be used to create any number
511 * of access-checked method handles, all checked against a single
512 * lookup class.
513 * <p>
514 * A {@code Lookup} object can be shared with other trusted code,
515 * such as a metaobject protocol.
516 * A shared {@code Lookup} object delegates the capability
517 * to create method handles on private members of the lookup class.
518 * Even if privileged code uses the {@code Lookup} object,
519 * the access checking is confined to the privileges of the
520 * original lookup class.
521 * <p>
522 * A lookup can fail, because
523 * the containing class is not accessible to the lookup class, or
524 * because the desired class member is missing, or because the
525 * desired class member is not accessible to the lookup class, or
526 * because the lookup object is not trusted enough to access the member.
527 * In the case of a field setter function on a {@code final} field,
528 * finality enforcement is treated as a kind of access control,
529 * and the lookup will fail, except in special cases of
530 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
531 * In any of these cases, a {@code ReflectiveOperationException} will be
532 * thrown from the attempted lookup. The exact class will be one of
533 * the following:
534 * <ul>
535 * <li>NoSuchMethodException — if a method is requested but does not exist
536 * <li>NoSuchFieldException — if a field is requested but does not exist
537 * <li>IllegalAccessException — if the member exists but an access check fails
538 * </ul>
539 * <p>
540 * In general, the conditions under which a method handle may be
541 * looked up for a method {@code M} are no more restrictive than the conditions
542 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
543 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
544 * a method handle lookup will generally raise a corresponding
545 * checked exception, such as {@code NoSuchMethodException}.
546 * And the effect of invoking the method handle resulting from the lookup
547 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
548 * to executing the compiled, verified, and resolved call to {@code M}.
549 * The same point is true of fields and constructors.
550 * <p style="font-size:smaller;">
551 * <em>Discussion:</em>
552 * Access checks only apply to named and reflected methods,
553 * constructors, and fields.
554 * Other method handle creation methods, such as
555 * {@link MethodHandle#asType MethodHandle.asType},
556 * do not require any access checks, and are used
557 * independently of any {@code Lookup} object.
558 * <p>
559 * If the desired member is {@code protected}, the usual JVM rules apply,
560 * including the requirement that the lookup class must either be in the
561 * same package as the desired member, or must inherit that member.
562 * (See the Java Virtual Machine Specification, sections {@jvms
563 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
564 * In addition, if the desired member is a non-static field or method
565 * in a different package, the resulting method handle may only be applied
566 * to objects of the lookup class or one of its subclasses.
567 * This requirement is enforced by narrowing the type of the leading
568 * {@code this} parameter from {@code C}
569 * (which will necessarily be a superclass of the lookup class)
570 * to the lookup class itself.
571 * <p>
572 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
573 * that the receiver argument must match both the resolved method <em>and</em>
574 * the current class. Again, this requirement is enforced by narrowing the
575 * type of the leading parameter to the resulting method handle.
576 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
577 * <p>
578 * The JVM represents constructors and static initializer blocks as internal methods
579 * with special names ({@code "<init>"} and {@code "<clinit>"}).
580 * The internal syntax of invocation instructions allows them to refer to such internal
581 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
582 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
583 * <p>
584 * If the relationship between nested types is expressed directly through the
585 * {@code NestHost} and {@code NestMembers} attributes
586 * (see the Java Virtual Machine Specification, sections {@jvms
587 * 4.7.28} and {@jvms 4.7.29}),
588 * then the associated {@code Lookup} object provides direct access to
589 * the lookup class and all of its nestmates
590 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
591 * Otherwise, access between nested classes is obtained by the Java compiler creating
592 * a wrapper method to access a private method of another class in the same nest.
593 * For example, a nested class {@code C.D}
594 * can access private members within other related classes such as
595 * {@code C}, {@code C.D.E}, or {@code C.B},
596 * but the Java compiler may need to generate wrapper methods in
597 * those related classes. In such cases, a {@code Lookup} object on
598 * {@code C.E} would be unable to access those private members.
599 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
600 * which can transform a lookup on {@code C.E} into one on any of those other
601 * classes, without special elevation of privilege.
602 * <p>
603 * The accesses permitted to a given lookup object may be limited,
604 * according to its set of {@link #lookupModes lookupModes},
605 * to a subset of members normally accessible to the lookup class.
606 * For example, the {@link MethodHandles#publicLookup publicLookup}
607 * method produces a lookup object which is only allowed to access
608 * public members in public classes of exported packages.
609 * The caller sensitive method {@link MethodHandles#lookup lookup}
610 * produces a lookup object with full capabilities relative to
611 * its caller class, to emulate all supported bytecode behaviors.
612 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
613 * with fewer access modes than the original lookup object.
614 *
615 * <p style="font-size:smaller;">
616 * <a id="privacc"></a>
617 * <em>Discussion of private and module access:</em>
618 * We say that a lookup has <em>private access</em>
619 * if its {@linkplain #lookupModes lookup modes}
620 * include the possibility of accessing {@code private} members
621 * (which includes the private members of nestmates).
622 * As documented in the relevant methods elsewhere,
623 * only lookups with private access possess the following capabilities:
624 * <ul style="font-size:smaller;">
625 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
626 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
627 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
628 * for classes accessible to the lookup class
629 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
630 * within the same package member
631 * </ul>
632 * <p style="font-size:smaller;">
633 * Similarly, a lookup with module access ensures that the original lookup creator was
634 * a member in the same module as the lookup class.
635 * <p style="font-size:smaller;">
636 * Private and module access are independently determined modes; a lookup may have
637 * either or both or neither. A lookup which possesses both access modes is said to
638 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}. Such a lookup has
639 * the following additional capability:
640 * <ul style="font-size:smaller;">
641 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
642 * such as {@code Class.forName}
643 * </ul>
644 * <p style="font-size:smaller;">
645 * Each of these permissions is a consequence of the fact that a lookup object
646 * with private access can be securely traced back to an originating class,
647 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
648 * can be reliably determined and emulated by method handles.
649 *
650 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
651 * When a lookup class in one module {@code M1} accesses a class in another module
652 * {@code M2}, extra access checking is performed beyond the access mode bits.
653 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
654 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
655 * and when the type is in a package of {@code M2} that is exported to
656 * at least {@code M1}.
657 * <p>
658 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
659 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
660 * MethodHandles.privateLookupIn} methods.
661 * Teleporting across modules will always record the original lookup class as
662 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
663 * and drops {@link Lookup#MODULE MODULE} access.
664 * If the target class is in the same module as the lookup class {@code C},
665 * then the target class becomes the new lookup class
666 * and there is no change to the previous lookup class.
667 * If the target class is in a different module from {@code M1} ({@code C}'s module),
668 * {@code C} becomes the new previous lookup class
669 * and the target class becomes the new lookup class.
670 * In that case, if there was already a previous lookup class in {@code M0},
671 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
672 * drops all privileges.
673 * For example,
674 * <blockquote><pre>
675 * {@code
676 * Lookup lookup = MethodHandles.lookup(); // in class C
677 * Lookup lookup2 = lookup.in(D.class);
678 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
679 * }</pre></blockquote>
680 * <p>
681 * The {@link #lookup()} factory method produces a {@code Lookup} object
682 * with {@code null} previous lookup class.
683 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
684 * to class {@code D} without elevation of privileges.
685 * If {@code C} and {@code D} are in the same module,
686 * {@code lookup2} records {@code D} as the new lookup class and keeps the
687 * same previous lookup class as the original {@code lookup}, or
688 * {@code null} if not present.
689 * <p>
690 * When a {@code Lookup} teleports from a class
691 * in one nest to another nest, {@code PRIVATE} access is dropped.
692 * When a {@code Lookup} teleports from a class in one package to
693 * another package, {@code PACKAGE} access is dropped.
694 * When a {@code Lookup} teleports from a class in one module to another module,
695 * {@code MODULE} access is dropped.
696 * Teleporting across modules drops the ability to access non-exported classes
697 * in both the module of the new lookup class and the module of the old lookup class
698 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
699 * A {@code Lookup} can teleport back and forth to a class in the module of
700 * the lookup class and the module of the previous class lookup.
701 * Teleporting across modules can only decrease access but cannot increase it.
702 * Teleporting to some third module drops all accesses.
703 * <p>
704 * In the above example, if {@code C} and {@code D} are in different modules,
705 * {@code lookup2} records {@code D} as its lookup class and
706 * {@code C} as its previous lookup class and {@code lookup2} has only
707 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
708 * {@code C}'s module and {@code D}'s module.
709 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
710 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
711 * class {@code D} is recorded as its previous lookup class.
712 * <p>
713 * Teleporting across modules restricts access to the public types that
714 * both the lookup class and the previous lookup class can equally access
715 * (see below).
716 * <p>
717 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
718 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
719 * and create a new {@code Lookup} with <a href="#privacc">private access</a>
720 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
721 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
722 * to call {@code privateLookupIn}.
723 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
724 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
725 * produces a new {@code Lookup} on {@code T} with full capabilities.
726 * A {@code lookup} on {@code C} is also allowed
727 * to do deep reflection on {@code T} in another module {@code M2} if
728 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
729 * the package containing {@code T} to at least {@code M1}.
730 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
731 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
732 * The resulting {@code Lookup} can be used to do member lookup or teleport
733 * to another lookup class by calling {@link #in Lookup::in}. But
734 * it cannot be used to obtain another private {@code Lookup} by calling
735 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
736 * because it has no {@code MODULE} access.
737 *
738 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
739 *
740 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
741 * allows cross-module access. The access checking is performed with respect
742 * to both the lookup class and the previous lookup class if present.
743 * <p>
744 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
745 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
746 * exported unconditionally}.
747 * <p>
748 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
749 * the lookup with {@link #PUBLIC} mode can access all public types in modules
750 * that are readable to {@code M1} and the type is in a package that is exported
751 * at least to {@code M1}.
752 * <p>
753 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
754 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
755 * the intersection of all public types that are accessible to {@code M1}
756 * with all public types that are accessible to {@code M0}. {@code M0}
757 * reads {@code M1} and hence the set of accessible types includes:
758 *
759 * <table class="striped">
760 * <caption style="display:none">
761 * Public types in the following packages are accessible to the
762 * lookup class and the previous lookup class.
763 * </caption>
764 * <thead>
765 * <tr>
766 * <th scope="col">Equally accessible types to {@code M0} and {@code M1}</th>
767 * </tr>
768 * </thead>
769 * <tbody>
770 * <tr>
771 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M1}</th>
772 * </tr>
773 * <tr>
774 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</th>
775 * </tr>
776 * <tr>
777 * <th scope="row" style="text-align:left">unconditional-exported packages from a third module {@code M2}
778 * if both {@code M0} and {@code M1} read {@code M2}</th>
779 * </tr>
780 * <tr>
781 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M1} to {@code M0}</th>
782 * </tr>
783 * <tr>
784 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M0} to {@code M1}
785 * if {@code M1} reads {@code M0}</th>
786 * </tr>
787 * <tr>
788 * <th scope="row" style="text-align:left">qualified-exported packages from a third module {@code M2} to
789 * both {@code M0} and {@code M1} if both {@code M0} and {@code M1} read {@code M2}</th>
790 * </tr>
791 * </tbody>
792 * </table>
793 *
794 * <h2><a id="access-modes"></a>Access modes</h2>
795 *
796 * The table below shows the access modes of a {@code Lookup} produced by
797 * any of the following factory or transformation methods:
798 * <ul>
799 * <li>{@link #lookup() MethodHandles::lookup}</li>
800 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
801 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
802 * <li>{@link Lookup#in Lookup::in}</li>
803 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
804 * </ul>
805 *
806 * <table class="striped">
807 * <caption style="display:none">
808 * Access mode summary
809 * </caption>
810 * <thead>
811 * <tr>
812 * <th scope="col">Lookup object</th>
813 * <th style="text-align:center">protected</th>
814 * <th style="text-align:center">private</th>
815 * <th style="text-align:center">package</th>
816 * <th style="text-align:center">module</th>
817 * <th style="text-align:center">public</th>
818 * </tr>
819 * </thead>
820 * <tbody>
821 * <tr>
822 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
823 * <td style="text-align:center">PRO</td>
824 * <td style="text-align:center">PRI</td>
825 * <td style="text-align:center">PAC</td>
826 * <td style="text-align:center">MOD</td>
827 * <td style="text-align:center">1R</td>
828 * </tr>
829 * <tr>
830 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
831 * <td></td>
832 * <td></td>
833 * <td style="text-align:center">PAC</td>
834 * <td style="text-align:center">MOD</td>
835 * <td style="text-align:center">1R</td>
836 * </tr>
837 * <tr>
838 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
839 * <td></td>
840 * <td></td>
841 * <td></td>
842 * <td style="text-align:center">MOD</td>
843 * <td style="text-align:center">1R</td>
844 * </tr>
845 * <tr>
846 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
847 * <td></td>
848 * <td></td>
849 * <td></td>
850 * <td></td>
851 * <td style="text-align:center">2R</td>
852 * </tr>
853 * <tr>
854 * <td>{@code CL.in(D).in(C)} hop back to module</td>
855 * <td></td>
856 * <td></td>
857 * <td></td>
858 * <td></td>
859 * <td style="text-align:center">2R</td>
860 * </tr>
861 * <tr>
862 * <td>{@code PRI1 = privateLookupIn(C1,CL)}</td>
863 * <td style="text-align:center">PRO</td>
864 * <td style="text-align:center">PRI</td>
865 * <td style="text-align:center">PAC</td>
866 * <td style="text-align:center">MOD</td>
867 * <td style="text-align:center">1R</td>
868 * </tr>
869 * <tr>
870 * <td>{@code PRI1a = privateLookupIn(C,PRI1)}</td>
871 * <td style="text-align:center">PRO</td>
872 * <td style="text-align:center">PRI</td>
873 * <td style="text-align:center">PAC</td>
874 * <td style="text-align:center">MOD</td>
875 * <td style="text-align:center">1R</td>
876 * </tr>
877 * <tr>
878 * <td>{@code PRI1.in(C1)} same package</td>
879 * <td></td>
880 * <td></td>
881 * <td style="text-align:center">PAC</td>
882 * <td style="text-align:center">MOD</td>
883 * <td style="text-align:center">1R</td>
884 * </tr>
885 * <tr>
886 * <td>{@code PRI1.in(C1)} different package</td>
887 * <td></td>
888 * <td></td>
889 * <td></td>
890 * <td style="text-align:center">MOD</td>
891 * <td style="text-align:center">1R</td>
892 * </tr>
893 * <tr>
894 * <td>{@code PRI1.in(D)} different module</td>
895 * <td></td>
896 * <td></td>
897 * <td></td>
898 * <td></td>
899 * <td style="text-align:center">2R</td>
900 * </tr>
901 * <tr>
902 * <td>{@code PRI1.dropLookupMode(PROTECTED)}</td>
903 * <td></td>
904 * <td style="text-align:center">PRI</td>
905 * <td style="text-align:center">PAC</td>
906 * <td style="text-align:center">MOD</td>
907 * <td style="text-align:center">1R</td>
908 * </tr>
909 * <tr>
910 * <td>{@code PRI1.dropLookupMode(PRIVATE)}</td>
911 * <td></td>
912 * <td></td>
913 * <td style="text-align:center">PAC</td>
914 * <td style="text-align:center">MOD</td>
915 * <td style="text-align:center">1R</td>
916 * </tr>
917 * <tr>
918 * <td>{@code PRI1.dropLookupMode(PACKAGE)}</td>
919 * <td></td>
920 * <td></td>
921 * <td></td>
922 * <td style="text-align:center">MOD</td>
923 * <td style="text-align:center">1R</td>
924 * </tr>
925 * <tr>
926 * <td>{@code PRI1.dropLookupMode(MODULE)}</td>
927 * <td></td>
928 * <td></td>
929 * <td></td>
930 * <td></td>
931 * <td style="text-align:center">1R</td>
932 * </tr>
933 * <tr>
934 * <td>{@code PRI1.dropLookupMode(PUBLIC)}</td>
935 * <td></td>
936 * <td></td>
937 * <td></td>
938 * <td></td>
939 * <td style="text-align:center">none</td>
940 * <tr>
941 * <td>{@code PRI2 = privateLookupIn(D,CL)}</td>
942 * <td style="text-align:center">PRO</td>
943 * <td style="text-align:center">PRI</td>
944 * <td style="text-align:center">PAC</td>
945 * <td></td>
946 * <td style="text-align:center">2R</td>
947 * </tr>
948 * <tr>
949 * <td>{@code privateLookupIn(D,PRI1)}</td>
950 * <td style="text-align:center">PRO</td>
951 * <td style="text-align:center">PRI</td>
952 * <td style="text-align:center">PAC</td>
953 * <td></td>
954 * <td style="text-align:center">2R</td>
955 * </tr>
956 * <tr>
957 * <td>{@code privateLookupIn(C,PRI2)} fails</td>
958 * <td></td>
959 * <td></td>
960 * <td></td>
961 * <td></td>
962 * <td style="text-align:center">IAE</td>
963 * </tr>
964 * <tr>
965 * <td>{@code PRI2.in(D2)} same package</td>
966 * <td></td>
967 * <td></td>
968 * <td style="text-align:center">PAC</td>
969 * <td></td>
970 * <td style="text-align:center">2R</td>
971 * </tr>
972 * <tr>
973 * <td>{@code PRI2.in(D2)} different package</td>
974 * <td></td>
975 * <td></td>
976 * <td></td>
977 * <td></td>
978 * <td style="text-align:center">2R</td>
979 * </tr>
980 * <tr>
981 * <td>{@code PRI2.in(C1)} hop back to module</td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td></td>
986 * <td style="text-align:center">2R</td>
987 * </tr>
988 * <tr>
989 * <td>{@code PRI2.in(E)} hop to third module</td>
990 * <td></td>
991 * <td></td>
992 * <td></td>
993 * <td></td>
994 * <td style="text-align:center">none</td>
995 * </tr>
996 * <tr>
997 * <td>{@code PRI2.dropLookupMode(PROTECTED)}</td>
998 * <td></td>
999 * <td style="text-align:center">PRI</td>
1000 * <td style="text-align:center">PAC</td>
1001 * <td></td>
1002 * <td style="text-align:center">2R</td>
1003 * </tr>
1004 * <tr>
1005 * <td>{@code PRI2.dropLookupMode(PRIVATE)}</td>
1006 * <td></td>
1007 * <td></td>
1008 * <td style="text-align:center">PAC</td>
1009 * <td></td>
1010 * <td style="text-align:center">2R</td>
1011 * </tr>
1012 * <tr>
1013 * <td>{@code PRI2.dropLookupMode(PACKAGE)}</td>
1014 * <td></td>
1015 * <td></td>
1016 * <td></td>
1017 * <td></td>
1018 * <td style="text-align:center">2R</td>
1019 * </tr>
1020 * <tr>
1021 * <td>{@code PRI2.dropLookupMode(MODULE)}</td>
1022 * <td></td>
1023 * <td></td>
1024 * <td></td>
1025 * <td></td>
1026 * <td style="text-align:center">2R</td>
1027 * </tr>
1028 * <tr>
1029 * <td>{@code PRI2.dropLookupMode(PUBLIC)}</td>
1030 * <td></td>
1031 * <td></td>
1032 * <td></td>
1033 * <td></td>
1034 * <td style="text-align:center">none</td>
1035 * </tr>
1036 * <tr>
1037 * <td>{@code CL.dropLookupMode(PROTECTED)}</td>
1038 * <td></td>
1039 * <td style="text-align:center">PRI</td>
1040 * <td style="text-align:center">PAC</td>
1041 * <td style="text-align:center">MOD</td>
1042 * <td style="text-align:center">1R</td>
1043 * </tr>
1044 * <tr>
1045 * <td>{@code CL.dropLookupMode(PRIVATE)}</td>
1046 * <td></td>
1047 * <td></td>
1048 * <td style="text-align:center">PAC</td>
1049 * <td style="text-align:center">MOD</td>
1050 * <td style="text-align:center">1R</td>
1051 * </tr>
1052 * <tr>
1053 * <td>{@code CL.dropLookupMode(PACKAGE)}</td>
1054 * <td></td>
1055 * <td></td>
1056 * <td></td>
1057 * <td style="text-align:center">MOD</td>
1058 * <td style="text-align:center">1R</td>
1059 * </tr>
1060 * <tr>
1061 * <td>{@code CL.dropLookupMode(MODULE)}</td>
1062 * <td></td>
1063 * <td></td>
1064 * <td></td>
1065 * <td></td>
1066 * <td style="text-align:center">1R</td>
1067 * </tr>
1068 * <tr>
1069 * <td>{@code CL.dropLookupMode(PUBLIC)}</td>
1070 * <td></td>
1071 * <td></td>
1072 * <td></td>
1073 * <td></td>
1074 * <td style="text-align:center">none</td>
1075 * </tr>
1076 * <tr>
1077 * <td>{@code PUB = publicLookup()}</td>
1078 * <td></td>
1079 * <td></td>
1080 * <td></td>
1081 * <td></td>
1082 * <td style="text-align:center">U</td>
1083 * </tr>
1084 * <tr>
1085 * <td>{@code PUB.in(D)} different module</td>
1086 * <td></td>
1087 * <td></td>
1088 * <td></td>
1089 * <td></td>
1090 * <td style="text-align:center">U</td>
1091 * </tr>
1092 * <tr>
1093 * <td>{@code PUB.in(D).in(E)} third module</td>
1094 * <td></td>
1095 * <td></td>
1096 * <td></td>
1097 * <td></td>
1098 * <td style="text-align:center">U</td>
1099 * </tr>
1100 * <tr>
1101 * <td>{@code PUB.dropLookupMode(UNCONDITIONAL)}</td>
1102 * <td></td>
1103 * <td></td>
1104 * <td></td>
1105 * <td></td>
1106 * <td style="text-align:center">none</td>
1107 * </tr>
1108 * <tr>
1109 * <td>{@code privateLookupIn(C1,PUB)} fails</td>
1110 * <td></td>
1111 * <td></td>
1112 * <td></td>
1113 * <td></td>
1114 * <td style="text-align:center">IAE</td>
1115 * </tr>
1116 * <tr>
1117 * <td>{@code ANY.in(X)}, for inaccessible {@code X}</td>
1118 * <td></td>
1119 * <td></td>
1120 * <td></td>
1121 * <td></td>
1122 * <td style="text-align:center">none</td>
1123 * </tr>
1124 * </tbody>
1125 * </table>
1126 *
1127 * <p>
1128 * Notes:
1129 * <ul>
1130 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1131 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1132 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1133 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1134 * <li>{@code PRO} indicates {@link #PROTECTED} bit set,
1135 * {@code PRI} indicates {@link #PRIVATE} bit set,
1136 * {@code PAC} indicates {@link #PACKAGE} bit set,
1137 * {@code MOD} indicates {@link #MODULE} bit set,
1138 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1139 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1140 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1141 * <li>Public access comes in three kinds:
1142 * <ul>
1143 * <li>unconditional ({@code U}): the lookup assumes readability.
1144 * The lookup has {@code null} previous lookup class.
1145 * <li>one-module-reads ({@code 1R}): the module access checking is
1146 * performed with respect to the lookup class. The lookup has {@code null}
1147 * previous lookup class.
1148 * <li>two-module-reads ({@code 2R}): the module access checking is
1149 * performed with respect to the lookup class and the previous lookup class.
1150 * The lookup has a non-null previous lookup class which is in a
1151 * different module from the current lookup class.
1152 * </ul>
1153 * <li>Any attempt to reach a third module loses all access.</li>
1154 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1155 * all access modes are dropped.</li>
1156 * </ul>
1157 *
1158 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1159 * Although bytecode instructions can only refer to classes in
1160 * a related class loader, this API can search for methods in any
1161 * class, as long as a reference to its {@code Class} object is
1162 * available. Such cross-loader references are also possible with the
1163 * Core Reflection API, and are impossible to bytecode instructions
1164 * such as {@code invokestatic} or {@code getfield}.
1165 * There is a {@linkplain java.lang.SecurityManager security manager API}
1166 * to allow applications to check such cross-loader references.
1167 * These checks apply to both the {@code MethodHandles.Lookup} API
1168 * and the Core Reflection API
1169 * (as found on {@link java.lang.Class Class}).
1170 * <p>
1171 * If a security manager is present, member and class lookups are subject to
1172 * additional checks.
1173 * From one to three calls are made to the security manager.
1174 * Any of these calls can refuse access by throwing a
1175 * {@link java.lang.SecurityException SecurityException}.
1176 * Define {@code smgr} as the security manager,
1177 * {@code lookc} as the lookup class of the current lookup object,
1178 * {@code refc} as the containing class in which the member
1179 * is being sought, and {@code defc} as the class in which the
1180 * member is actually defined.
1181 * (If a class or other type is being accessed,
1182 * the {@code refc} and {@code defc} values are the class itself.)
1183 * The value {@code lookc} is defined as <em>not present</em>
1184 * if the current lookup object does not have
1185 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1186 * The calls are made according to the following rules:
1187 * <ul>
1188 * <li><b>Step 1:</b>
1189 * If {@code lookc} is not present, or if its class loader is not
1190 * the same as or an ancestor of the class loader of {@code refc},
1191 * then {@link SecurityManager#checkPackageAccess
1192 * smgr.checkPackageAccess(refcPkg)} is called,
1193 * where {@code refcPkg} is the package of {@code refc}.
1194 * <li><b>Step 2a:</b>
1195 * If the retrieved member is not public and
1196 * {@code lookc} is not present, then
1197 * {@link SecurityManager#checkPermission smgr.checkPermission}
1198 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1199 * <li><b>Step 2b:</b>
1200 * If the retrieved class has a {@code null} class loader,
1201 * and {@code lookc} is not present, then
1202 * {@link SecurityManager#checkPermission smgr.checkPermission}
1203 * with {@code RuntimePermission("getClassLoader")} is called.
1204 * <li><b>Step 3:</b>
1205 * If the retrieved member is not public,
1206 * and if {@code lookc} is not present,
1207 * and if {@code defc} and {@code refc} are different,
1208 * then {@link SecurityManager#checkPackageAccess
1209 * smgr.checkPackageAccess(defcPkg)} is called,
1210 * where {@code defcPkg} is the package of {@code defc}.
1211 * </ul>
1212 * Security checks are performed after other access checks have passed.
1213 * Therefore, the above rules presuppose a member or class that is public,
1214 * or else that is being accessed from a lookup class that has
1215 * rights to access the member or class.
1216 * <p>
1217 * If a security manager is present and the current lookup object does not have
1218 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1219 * {@link #defineClass(byte[]) defineClass}
1220 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1221 * with {@code RuntimePermission("defineClass")}.
1222 *
1223 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1224 * A small number of Java methods have a special property called caller sensitivity.
1225 * A <em>caller-sensitive</em> method can behave differently depending on the
1226 * identity of its immediate caller.
1227 * <p>
1228 * If a method handle for a caller-sensitive method is requested,
1229 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1230 * but they take account of the lookup class in a special way.
1231 * The resulting method handle behaves as if it were called
1232 * from an instruction contained in the lookup class,
1233 * so that the caller-sensitive method detects the lookup class.
1234 * (By contrast, the invoker of the method handle is disregarded.)
1235 * Thus, in the case of caller-sensitive methods,
1236 * different lookup classes may give rise to
1237 * differently behaving method handles.
1238 * <p>
1239 * In cases where the lookup object is
1240 * {@link MethodHandles#publicLookup() publicLookup()},
1241 * or some other lookup object without the
1242 * {@linkplain #hasFullPrivilegeAccess() full privilege access},
1243 * the lookup class is disregarded.
1244 * In such cases, no caller-sensitive method handle can be created,
1245 * access is forbidden, and the lookup fails with an
1246 * {@code IllegalAccessException}.
1247 * <p style="font-size:smaller;">
1248 * <em>Discussion:</em>
1249 * For example, the caller-sensitive method
1250 * {@link java.lang.Class#forName(String) Class.forName(x)}
1251 * can return varying classes or throw varying exceptions,
1252 * depending on the class loader of the class that calls it.
1253 * A public lookup of {@code Class.forName} will fail, because
1254 * there is no reasonable way to determine its bytecode behavior.
1255 * <p style="font-size:smaller;">
1256 * If an application caches method handles for broad sharing,
1257 * it should use {@code publicLookup()} to create them.
1258 * If there is a lookup of {@code Class.forName}, it will fail,
1259 * and the application must take appropriate action in that case.
1260 * It may be that a later lookup, perhaps during the invocation of a
1261 * bootstrap method, can incorporate the specific identity
1262 * of the caller, making the method accessible.
1263 * <p style="font-size:smaller;">
1264 * The function {@code MethodHandles.lookup} is caller sensitive
1265 * so that there can be a secure foundation for lookups.
1266 * Nearly all other methods in the JSR 292 API rely on lookup
1267 * objects to check access requests.
1268 *
1269 * @revised 9
1270 */
1271 public static final
1272 class Lookup {
1273 /** The class on behalf of whom the lookup is being performed. */
1274 private final Class<?> lookupClass;
1275
1276 /** previous lookup class */
1277 private final Class<?> prevLookupClass;
1278
1279 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1280 private final int allowedModes;
1281
1282 static {
1283 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1284 }
1285
1286 /** A single-bit mask representing {@code public} access,
1287 * which may contribute to the result of {@link #lookupModes lookupModes}.
1288 * The value, {@code 0x01}, happens to be the same as the value of the
1289 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1290 * <p>
1291 * A {@code Lookup} with this lookup mode performs cross-module access check
1292 * with respect to the {@linkplain #lookupClass() lookup class} and
1293 * {@linkplain #previousLookupClass() previous lookup class} if present.
1294 */
1295 public static final int PUBLIC = Modifier.PUBLIC;
1296
1297 /** A single-bit mask representing {@code private} access,
1298 * which may contribute to the result of {@link #lookupModes lookupModes}.
1299 * The value, {@code 0x02}, happens to be the same as the value of the
1300 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1301 */
1302 public static final int PRIVATE = Modifier.PRIVATE;
1303
1304 /** A single-bit mask representing {@code protected} access,
1305 * which may contribute to the result of {@link #lookupModes lookupModes}.
1306 * The value, {@code 0x04}, happens to be the same as the value of the
1307 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1308 */
1309 public static final int PROTECTED = Modifier.PROTECTED;
1310
1311 /** A single-bit mask representing {@code package} access (default access),
1312 * which may contribute to the result of {@link #lookupModes lookupModes}.
1313 * The value is {@code 0x08}, which does not correspond meaningfully to
1314 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1315 */
1316 public static final int PACKAGE = Modifier.STATIC;
1317
1318 /** A single-bit mask representing {@code module} access,
1319 * which may contribute to the result of {@link #lookupModes lookupModes}.
1320 * The value is {@code 0x10}, which does not correspond meaningfully to
1321 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1322 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1323 * with this lookup mode can access all public types in the module of the
1324 * lookup class and public types in packages exported by other modules
1325 * to the module of the lookup class.
1326 * <p>
1327 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1328 * previous lookup class} is always {@code null}.
1329 *
1330 * @since 9
1331 * @spec JPMS
1332 */
1333 public static final int MODULE = PACKAGE << 1;
1334
1335 /** A single-bit mask representing {@code unconditional} access
1336 * which may contribute to the result of {@link #lookupModes lookupModes}.
1337 * The value is {@code 0x20}, which does not correspond meaningfully to
1338 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1339 * A {@code Lookup} with this lookup mode assumes {@linkplain
1340 * java.lang.Module#canRead(java.lang.Module) readability}.
1341 * This lookup mode can access all public members of public types
1342 * of all modules when the type is in a package that is {@link
1343 * java.lang.Module#isExported(String) exported unconditionally}.
1344 *
1345 * <p>
1346 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1347 * previous lookup class} is always {@code null}.
1348 *
1349 * @since 9
1350 * @spec JPMS
1351 * @see #publicLookup()
1352 */
1353 public static final int UNCONDITIONAL = PACKAGE << 2;
1354
1355 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
1356 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
1357 private static final int TRUSTED = -1;
1358
1359 /*
1360 * Adjust PUBLIC => PUBLIC|MODULE|UNCONDITIONAL
1361 * Adjust 0 => PACKAGE
1362 */
1363 private static int fixmods(int mods) {
1364 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
1365 if (Modifier.isPublic(mods))
1366 mods |= UNCONDITIONAL;
1367 return (mods != 0) ? mods : PACKAGE;
1368 }
1369
1370 /** Tells which class is performing the lookup. It is this class against
1371 * which checks are performed for visibility and access permissions.
1372 * <p>
1373 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1374 * access checks are performed against both the lookup class and the previous lookup class.
1375 * <p>
1376 * The class implies a maximum level of access permission,
1377 * but the permissions may be additionally limited by the bitmask
1378 * {@link #lookupModes lookupModes}, which controls whether non-public members
1379 * can be accessed.
1380 * @return the lookup class, on behalf of which this lookup object finds members
1381 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1382 */
1383 public Class<?> lookupClass() {
1384 return lookupClass;
1385 }
1386
1387 /** Reports a lookup class in another module that this lookup object
1388 * was previously teleported from, or {@code null}.
1389 * <p>
1390 * A {@code Lookup} object produced by the factory methods, such as the
1391 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1392 * has {@code null} previous lookup class.
1393 * A {@code Lookup} object has a non-null previous lookup class
1394 * when this lookup was teleported from an old lookup class
1395 * in one module to a new lookup class in another module.
1396 *
1397 * @return the lookup class in another module that this lookup object was
1398 * previously teleported from, or {@code null}
1399 * @since 14
1400 * @see #in(Class)
1401 * @see MethodHandles#privateLookupIn(Class, Lookup)
1402 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1403 */
1404 public Class<?> previousLookupClass() {
1405 return prevLookupClass;
1406 }
1407
1408 // This is just for calling out to MethodHandleImpl.
1409 private Class<?> lookupClassOrNull() {
1410 if (allowedModes == TRUSTED) {
1411 return null;
1412 }
1413 if (allowedModes == UNCONDITIONAL) {
1414 // use Object as the caller to pass to VM doing resolution
1415 return Object.class;
1416 }
1417 return lookupClass;
1418 }
1419
1420 /** Tells which access-protection classes of members this lookup object can produce.
1421 * The result is a bit-mask of the bits
1422 * {@linkplain #PUBLIC PUBLIC (0x01)},
1423 * {@linkplain #PRIVATE PRIVATE (0x02)},
1424 * {@linkplain #PROTECTED PROTECTED (0x04)},
1425 * {@linkplain #PACKAGE PACKAGE (0x08)},
1426 * {@linkplain #MODULE MODULE (0x10)},
1427 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
1428 * <p>
1429 * A freshly-created lookup object
1430 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1431 * all possible bits set, except {@code UNCONDITIONAL}.
1432 * A lookup object on a new lookup class
1433 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1434 * may have some mode bits set to zero.
1435 * Mode bits can also be
1436 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1437 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1438 * The purpose of this is to restrict access via the new lookup object,
1439 * so that it can access only names which can be reached by the original
1440 * lookup object, and also by the new lookup class.
1441 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1442 * @see #in
1443 * @see #dropLookupMode
1444 *
1445 * @revised 9
1446 * @spec JPMS
1447 */
1448 public int lookupModes() {
1449 return allowedModes & ALL_MODES;
1450 }
1451
1452 /** Embody the current class (the lookupClass) as a lookup class
1453 * for method handle creation.
1454 * Must be called by from a method in this package,
1455 * which in turn is called by a method not in this package.
1456 */
1457 Lookup(Class<?> lookupClass) {
1458 this(lookupClass, null, FULL_POWER_MODES);
1459 }
1460
1461 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1462 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1463 && prevLookupClass.getModule() != lookupClass.getModule());
1464 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1465 this.lookupClass = lookupClass;
1466 this.prevLookupClass = prevLookupClass;
1467 this.allowedModes = allowedModes;
1468 }
1469
1470 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1471 // make sure we haven't accidentally picked up a privileged class:
1472 checkUnprivilegedlookupClass(lookupClass);
1473 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1474 }
1475
1476 /**
1477 * Creates a lookup on the specified new lookup class.
1478 * The resulting object will report the specified
1479 * class as its own {@link #lookupClass() lookupClass}.
1480 *
1481 * <p>
1482 * However, the resulting {@code Lookup} object is guaranteed
1483 * to have no more access capabilities than the original.
1484 * In particular, access capabilities can be lost as follows:<ul>
1485 * <li>If the new lookup class is in a different module from the old one,
1486 * i.e. {@link #MODULE MODULE} access is lost.
1487 * <li>If the new lookup class is in a different package
1488 * than the old one, protected and default (package) members will not be accessible,
1489 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1490 * <li>If the new lookup class is not within the same package member
1491 * as the old one, private members will not be accessible, and protected members
1492 * will not be accessible by virtue of inheritance,
1493 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1494 * (Protected members may continue to be accessible because of package sharing.)
1495 * <li>If the new lookup class is not
1496 * {@linkplain #accessClass(Class) accessible} to this lookup,
1497 * then no members, not even public members, will be accessible
1498 * i.e. all access modes are lost.
1499 * <li>If the new lookup class, the old lookup class and the previous lookup class
1500 * are all in different modules i.e. teleporting to a third module,
1501 * all access modes are lost.
1502 * </ul>
1503 * <p>
1504 * The new previous lookup class is chosen as follows:
1505 * <ul>
1506 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1507 * the new previous lookup class is {@code null}.
1508 * <li>If the new lookup class is in the same module as the old lookup class,
1509 * the new previous lookup class is the old previous lookup class.
1510 * <li>If the new lookup class is in a different module from the old lookup class,
1511 * the new previous lookup class is the old lookup class.
1512 *</ul>
1513 * <p>
1514 * The resulting lookup's capabilities for loading classes
1515 * (used during {@link #findClass} invocations)
1516 * are determined by the lookup class' loader,
1517 * which may change due to this operation.
1518 * <p>
1519 * @param requestedLookupClass the desired lookup class for the new lookup object
1520 * @return a lookup object which reports the desired lookup class, or the same object
1521 * if there is no change
1522 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1523 * @throws NullPointerException if the argument is null
1524 *
1525 * @revised 9
1526 * @spec JPMS
1527 * @see #accessClass(Class)
1528 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1529 */
1530 public Lookup in(Class<?> requestedLookupClass) {
1531 Objects.requireNonNull(requestedLookupClass);
1532 if (requestedLookupClass.isPrimitive())
1533 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1534 if (requestedLookupClass.isArray())
1535 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1536
1537 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1538 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1539 if (requestedLookupClass == this.lookupClass)
1540 return this; // keep same capabilities
1541 int newModes = (allowedModes & FULL_POWER_MODES);
1542 Module fromModule = this.lookupClass.getModule();
1543 Module targetModule = requestedLookupClass.getModule();
1544 Class<?> plc = this.previousLookupClass();
1545 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1546 assert plc == null;
1547 newModes = UNCONDITIONAL;
1548 } else if (fromModule != targetModule) {
1549 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1550 // allow hopping back and forth between fromModule and plc's module
1551 // but not the third module
1552 newModes = 0;
1553 }
1554 // drop MODULE access
1555 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1556 // teleport from this lookup class
1557 plc = this.lookupClass;
1558 }
1559 if ((newModes & PACKAGE) != 0
1560 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1561 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1562 }
1563 // Allow nestmate lookups to be created without special privilege:
1564 if ((newModes & PRIVATE) != 0
1565 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1566 newModes &= ~(PRIVATE|PROTECTED);
1567 }
1568 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1569 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1570 // The requested class it not accessible from the lookup class.
1571 // No permissions.
1572 newModes = 0;
1573 }
1574 return newLookup(requestedLookupClass, plc, newModes);
1575 }
1576
1577 /**
1578 * Creates a lookup on the same lookup class which this lookup object
1579 * finds members, but with a lookup mode that has lost the given lookup mode.
1580 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1581 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1582 * {@link #PRIVATE PRIVATE}, or {@link #UNCONDITIONAL UNCONDITIONAL}.
1583 *
1584 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1585 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1586 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1587 * lookup has no access.
1588 *
1589 * <p> If this lookup is not a public lookup, then the following applies
1590 * regardless of its {@linkplain #lookupModes() lookup modes}.
1591 * {@link #PROTECTED PROTECTED} is always dropped and so the resulting lookup
1592 * mode will never have this access capability. When dropping {@code PACKAGE}
1593 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1594 * access. When dropping {@code MODULE} then the resulting lookup will not
1595 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1596 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1597 *
1598 * @apiNote
1599 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1600 * delegate non-public access within the package of the lookup class without
1601 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1602 * A lookup with {@code MODULE} but not
1603 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1604 * the module of the lookup class without conferring package access.
1605 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1606 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1607 * to public classes accessible to both the module of the lookup class
1608 * and the module of the previous lookup class.
1609 *
1610 * @param modeToDrop the lookup mode to drop
1611 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1612 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1613 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
1614 * @see MethodHandles#privateLookupIn
1615 * @since 9
1616 */
1617 public Lookup dropLookupMode(int modeToDrop) {
1618 int oldModes = lookupModes();
1619 int newModes = oldModes & ~(modeToDrop | PROTECTED);
1620 switch (modeToDrop) {
1621 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1622 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1623 case PACKAGE: newModes &= ~(PRIVATE); break;
1624 case PROTECTED:
1625 case PRIVATE:
1626 case UNCONDITIONAL: break;
1627 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1628 }
1629 if (newModes == oldModes) return this; // return self if no change
1630 return newLookup(lookupClass(), previousLookupClass(), newModes);
1631 }
1632
1633 /**
1634 * Creates a class or interface from {@code bytes}
1635 * with the same class loader and in the same runtime package and
1636 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1637 * {@linkplain #lookupClass() lookup class} as if calling
1638 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1639 * ClassLoader::defineClass}.
1640 *
1641 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1642 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1643 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1644 * that the lookup object was created by a caller in the runtime package (or derived
1645 * from a lookup originally created by suitably privileged code to a target class in
1646 * the runtime package). </p>
1647 *
1648 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1649 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1650 * same package as the lookup class. </p>
1651 *
1652 * <p> This method does not run the class initializer. The class initializer may
1653 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1654 * Specification</em>. </p>
1655 *
1656 * <p> If there is a security manager and this lookup does not have {@linkplain
1657 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1658 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1659 *
1660 * @param bytes the class bytes
1661 * @return the {@code Class} object for the class
1662 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1663 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1664 * @throws IllegalArgumentException the bytes are for a class in a different package
1665 * to the lookup class
1666 * @throws VerifyError if the newly created class cannot be verified
1667 * @throws LinkageError if the newly created class cannot be linked for any other reason
1668 * @throws SecurityException if a security manager is present and it
1669 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1670 * @throws NullPointerException if {@code bytes} is {@code null}
1671 * @since 9
1672 * @spec JPMS
1673 * @see Lookup#privateLookupIn
1674 * @see Lookup#dropLookupMode
1675 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1676 */
1677 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1678 ensureDefineClassPermission();
1679 if ((lookupModes() & PACKAGE) == 0)
1680 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1681 return makeClassDefiner(bytes.clone()).defineClass(false);
1682 }
1683
1684 private void ensureDefineClassPermission() {
1685 if (allowedModes == TRUSTED) return;
1686
1687 if (!hasFullPrivilegeAccess()) {
1688 SecurityManager sm = System.getSecurityManager();
1689 if (sm != null)
1690 sm.checkPermission(new RuntimePermission("defineClass"));
1691 }
1692 }
1693
1694 /**
1695 * The set of class options that specify whether a hidden class created by
1696 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1697 * Lookup::defineHiddenClass} method is dynamically added as a new member
1698 * to the nest of a lookup class and/or whether a hidden class has
1699 * a strong relationship with the class loader marked as its defining loader.
1700 *
1701 * @since 15
1702 */
1703 public enum ClassOption {
1704 /**
1705 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1706 * of a lookup class as a nestmate.
1707 *
1708 * <p> A hidden nestmate class has access to the private members of all
1709 * classes and interfaces in the same nest.
1710 *
1711 * @see Class#getNestHost()
1712 */
1713 NESTMATE(NESTMATE_CLASS),
1714
1715 /**
1716 * Specifies that a hidden class has a <em>strong</em>
1717 * relationship with the class loader marked as its defining loader,
1718 * as a normal class or interface has with its own defining loader.
1719 * This means that the hidden class may be unloaded if and only if
1720 * its defining loader is not reachable and thus may be reclaimed
1721 * by a garbage collector (JLS 12.7).
1722 *
1723 * <p> By default, a hidden class or interface may be unloaded
1724 * even if the class loader that is marked as its defining loader is
1725 * <a href="../ref/package.html#reachability">reachable</a>.
1726
1727 *
1728 * @jls 12.7 Unloading of Classes and Interfaces
1729 */
1730 STRONG(STRONG_LOADER_LINK);
1731
1732 /* the flag value is used by VM at define class time */
1733 private final int flag;
1734 ClassOption(int flag) {
1735 this.flag = flag;
1736 }
1737
1738 static int optionsToFlag(Set<ClassOption> options) {
1739 int flags = 0;
1740 for (ClassOption cp : options) {
1741 flags |= cp.flag;
1742 }
1743 return flags;
1744 }
1745 }
1746
1747 /**
1748 * Creates a <em>hidden</em> class or interface from {@code bytes},
1749 * returning a {@code Lookup} on the newly created class or interface.
1750 *
1751 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1752 * which either defines {@code C} directly or delegates to another class loader.
1753 * A class loader defines {@code C} directly by invoking
1754 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1755 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1756 * to derive {@code C} from a purported representation in {@code class} file format.
1757 * In situations where use of a class loader is undesirable, a class or interface
1758 * {@code C} can be created by this method instead. This method is capable of
1759 * defining {@code C}, and thereby creating it, without invoking
1760 * {@code ClassLoader::defineClass}.
1761 * Instead, this method defines {@code C} as if by arranging for
1762 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1763 * from a purported representation in {@code class} file format
1764 * using the following rules:
1765 *
1766 * <ol>
1767 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1768 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1769 * This level of access is needed to create {@code C} in the module
1770 * of the lookup class of this {@code Lookup}.</li>
1771 *
1772 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1773 * structure of a supported major and minor version. The major and minor version
1774 * may differ from the {@code class} file version of the lookup class of this
1775 * {@code Lookup}.</li>
1776 *
1777 * <li> The value of {@code this_class} must be a valid index in the
1778 * {@code constant_pool} table, and the entry at that index must be a valid
1779 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1780 * encoded in internal form that is specified by this structure. {@code N} must
1781 * denote a class or interface in the same package as the lookup class.</li>
1782 *
1783 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1784 * where {@code <suffix>} is an unqualified name.
1785 *
1786 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1787 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1788 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1789 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1790 * refers to the new {@code CONSTANT_Utf8_info} structure.
1791 *
1792 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1793 *
1794 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1795 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1796 * with the following adjustments:
1797 * <ul>
1798 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1799 * that includes a single {@code "."} character, even though this is not a valid
1800 * binary class or interface name in internal form.</li>
1801 *
1802 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1803 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1804 *
1805 * <li> {@code C} is considered to have the same runtime
1806 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1807 * and {@linkplain java.security.ProtectionDomain protection domain}
1808 * as the lookup class of this {@code Lookup}.
1809 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1810 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1811 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1812 * <ul>
1813 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>}, even
1814 * though this is not a valid binary class or interface name.</li>
1815 * <li> {@link Class#descriptorString()} returns the string {@code "L" + CN + ";" },
1816 * even though this is not a valid type descriptor name.</li>
1817 * </ul>
1818 * </ul>
1819 * </li>
1820 * </ol>
1821 *
1822 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1823 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1824 * <ul>
1825 * <li> During verification, whenever it is necessary to load the class named
1826 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
1827 * made of any class loader.</li>
1828 *
1829 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
1830 * by {@code this_class}, the symbolic reference is considered to be resolved to
1831 * {@code C} and resolution always succeeds immediately.</li>
1832 * </ul>
1833 *
1834 * <p> If the {@code initialize} parameter is {@code true},
1835 * then {@code C} is initialized by the Java Virtual Machine.
1836 *
1837 * <p> The newly created class or interface {@code C} serves as the
1838 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
1839 * returned by this method. {@code C} is <em>hidden</em> in the sense that
1840 * no other class or interface can refer to {@code C} via a constant pool entry.
1841 * That is, a hidden class or interface cannot be named as a supertype, a field type,
1842 * a method parameter type, or a method return type by any other class.
1843 * This is because a hidden class or interface does not have a binary name, so
1844 * there is no internal form available to record in any class's constant pool.
1845 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
1846 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
1847 * is not {@linkplain java.lang.instrument.Instrumentation#isModifiableClass(Class)
1848 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
1849 * JVM Tool Interface</a>.
1850 *
1851 * <p> A class or interface created by
1852 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1853 * a class loader} has a strong relationship with that class loader.
1854 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
1855 * that {@linkplain Class#getClassLoader() defined it}.
1856 * This means that a class created by a class loader may be unloaded if and
1857 * only if its defining loader is not reachable and thus may be reclaimed
1858 * by a garbage collector (JLS 12.7).
1859 *
1860 * By default, however, a hidden class or interface may be unloaded even if
1861 * the class loader that is marked as its defining loader is
1862 * <a href="../ref/package.html#reachability">reachable</a>.
1863 * This behavior is useful when a hidden class or interface serves multiple
1864 * classes defined by arbitrary class loaders. In other cases, a hidden
1865 * class or interface may be linked to a single class (or a small number of classes)
1866 * with the same defining loader as the hidden class or interface.
1867 * In such cases, where the hidden class or interface must be coterminous
1868 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
1869 * option may be passed in {@code options}.
1870 * This arranges for a hidden class to have the same strong relationship
1871 * with the class loader marked as its defining loader,
1872 * as a normal class or interface has with its own defining loader.
1873 *
1874 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
1875 * may still prevent a hidden class or interface from being
1876 * unloaded by ensuring that the {@code Class} object is reachable.
1877 *
1878 * <p> The unloading characteristics are set for each hidden class when it is
1879 * defined, and cannot be changed later. An advantage of allowing hidden classes
1880 * to be unloaded independently of the class loader marked as their defining loader
1881 * is that a very large number of hidden classes may be created by an application.
1882 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
1883 * just as if normal classes were created by class loaders.
1884 *
1885 * <p> Classes and interfaces in a nest are allowed to have mutual access to
1886 * their private members. The nest relationship is determined by
1887 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
1888 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
1889 * By default, a hidden class belongs to a nest consisting only of itself
1890 * because a hidden class has no binary name.
1891 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
1892 * to create a hidden class or interface {@code C} as a member of a nest.
1893 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
1894 * in the {@code ClassFile} structure from which {@code C} was derived.
1895 * Instead, the following rules determine the nest host of {@code C}:
1896 * <ul>
1897 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
1898 * been determined, then let {@code H} be the nest host of the lookup class.
1899 * Otherwise, the nest host of the lookup class is determined using the
1900 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
1901 * <li>The nest host of {@code C} is determined to be {@code H},
1902 * the nest host of the lookup class.</li>
1903 * </ul>
1904 *
1905 * <p> A hidden class or interface may be serializable, but this requires a custom
1906 * serialization mechanism in order to ensure that instances are properly serialized
1907 * and deserialized. The default serialization mechanism supports only classes and
1908 * interfaces that are discoverable by their class name.
1909 *
1910 * @param bytes the bytes that make up the class data,
1911 * in the format of a valid {@code class} file as defined by
1912 * <cite>The Java Virtual Machine Specification</cite>.
1913 * @param initialize if {@code true} the class will be initialized.
1914 * @param options {@linkplain ClassOption class options}
1915 * @return the {@code Lookup} object on the hidden class
1916 *
1917 * @throws IllegalAccessException if this {@code Lookup} does not have
1918 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
1919 * @throws SecurityException if a security manager is present and it
1920 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1921 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1922 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
1923 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
1924 * {@bytes} denotes a class in a different package than the lookup class
1925 * @throws IncompatibleClassChangeError if the class or interface named as
1926 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
1927 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
1928 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
1929 * {@code C} is {@code C} itself
1930 * @throws VerifyError if the newly created class cannot be verified
1931 * @throws LinkageError if the newly created class cannot be linked for any other reason
1932 * @throws NullPointerException if any parameter is {@code null}
1933 *
1934 * @since 15
1935 * @see Class#isHidden()
1936 * @jvms 4.2.1 Binary Class and Interface Names
1937 * @jvms 4.2.2 Unqualified Names
1938 * @jvms 4.7.28 The {@code NestHost} Attribute
1939 * @jvms 4.7.29 The {@code NestMembers} Attribute
1940 * @jvms 5.4.3.1 Class and Interface Resolution
1941 * @jvms 5.4.4 Access Control
1942 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
1943 * @jvms 5.4 Linking
1944 * @jvms 5.5 Initialization
1945 * @jls 12.7 Unloading of Classes and Interfaces
1946 */
1947 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
1948 throws IllegalAccessException
1949 {
1950 Objects.requireNonNull(bytes);
1951 Objects.requireNonNull(options);
1952
1953 ensureDefineClassPermission();
1954 if (!hasFullPrivilegeAccess()) {
1955 throw new IllegalAccessException(this + " does not have full privilege access");
1956 }
1957
1958 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
1959 }
1960
1961 /**
1962 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
1963 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
1964 * returning a {@code Lookup} on the newly created class or interface.
1965 *
1966 * <p> This method is equivalent to calling
1967 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, true, options)}
1968 * as if the hidden class has a private static final unnamed field whose value
1969 * is initialized to {@code classData} right before the class initializer is
1970 * executed. The newly created class is linked and initialized by the Java
1971 * Virtual Machine.
1972 *
1973 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
1974 * method can be used to retrieve the {@code classData}.
1975 *
1976 * @param bytes the class bytes
1977 * @param classData pre-initialized class data
1978 * @param options {@linkplain ClassOption class options}
1979 * @return the {@code Lookup} object on the hidden class
1980 *
1981 * @throws IllegalAccessException if this {@code Lookup} does not have
1982 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
1983 * @throws SecurityException if a security manager is present and it
1984 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1985 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1986 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
1987 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
1988 * {@bytes} denotes a class in a different package than the lookup class
1989 * @throws IncompatibleClassChangeError if the class or interface named as
1990 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
1991 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
1992 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
1993 * {@code C} is {@code C} itself
1994 * @throws VerifyError if the newly created class cannot be verified
1995 * @throws LinkageError if the newly created class cannot be linked for any other reason
1996 * @throws NullPointerException if any parameter is {@code null}
1997 *
1998 * @since 15
1999 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2000 * @see Class#isHidden()
2001 */
2002 /* package-private */ Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, ClassOption... options)
2003 throws IllegalAccessException
2004 {
2005 Objects.requireNonNull(bytes);
2006 Objects.requireNonNull(classData);
2007 Objects.requireNonNull(options);
2008
2009 ensureDefineClassPermission();
2010 if (!hasFullPrivilegeAccess()) {
2011 throw new IllegalAccessException(this + " does not have full privilege access");
2012 }
2013
2014 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2015 .defineClassAsLookup(true, classData);
2016 }
2017
2018 /*
2019 * Validates the given bytes to be a class or interface and the class name
2020 * is in the same package as the lookup class.
2021 *
2022 * This method returns the class name.
2023 */
2024 private String validateAndGetClassName(byte[] bytes) {
2025 try {
2026 ClassReader reader = new ClassReader(bytes);
2027 if ((reader.getAccess() & Opcodes.ACC_MODULE) != 0) {
2028 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2029 }
2030 String name = reader.getClassName().replace('/', '.');
2031 int index = name.lastIndexOf('.');
2032 String pn = (index == -1) ? "" : name.substring(0, index);
2033 if (!pn.equals(lookupClass.getPackageName())) {
2034 throw newIllegalArgumentException(name + " not in same package as lookup class: " +
2035 lookupClass.getName());
2036 }
2037 return name;
2038 } catch (IllegalArgumentException e) {
2039 throw e;
2040 } catch (RuntimeException e) {
2041 // ASM exceptions are poorly specified
2042 ClassFormatError cfe = new ClassFormatError();
2043 cfe.initCause(e);
2044 throw cfe;
2045 }
2046 }
2047
2048
2049 /*
2050 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2051 * from the given bytes.
2052 *
2053 * Caller should make a defensive copy of the arguments if needed
2054 * before calling this factory method.
2055 *
2056 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2057 * {@bytes} denotes a class in a different package than the lookup class
2058 */
2059 private ClassDefiner makeClassDefiner(byte[] bytes) {
2060 return new ClassDefiner(this, validateAndGetClassName(bytes), bytes, STRONG_LOADER_LINK);
2061 }
2062
2063 /**
2064 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2065 * from the given bytes. The name must be in the same package as the lookup class.
2066 *
2067 * Caller should make a defensive copy of the arguments if needed
2068 * before calling this factory method.
2069 *
2070 * @param bytes class bytes
2071 * @return ClassDefiner that defines a hidden class of the given bytes.
2072 *
2073 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2074 * {@bytes} denotes a class in a different package than the lookup class
2075 */
2076 ClassDefiner makeHiddenClassDefiner(byte[] bytes) {
2077 return makeHiddenClassDefiner(validateAndGetClassName(bytes), bytes, Set.of(), false);
2078 }
2079
2080 /**
2081 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2082 * from the given bytes and options.
2083 * The name must be in the same package as the lookup class.
2084 *
2085 * Caller should make a defensive copy of the arguments if needed
2086 * before calling this factory method.
2087 *
2088 * @param bytes class bytes
2089 * @param options class options
2090 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2091 * @return ClassDefiner that defines a hidden class of the given bytes and options
2092 *
2093 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2094 * {@bytes} denotes a class in a different package than the lookup class
2095 */
2096 ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2097 Set<ClassOption> options,
2098 boolean accessVmAnnotations) {
2099 return makeHiddenClassDefiner(validateAndGetClassName(bytes), bytes, options, accessVmAnnotations);
2100 }
2101
2102 /**
2103 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2104 * from the given bytes. No package name check on the given name.
2105 *
2106 * @param name fully-qualified name that specifies the prefix of the hidden class
2107 * @param bytes class bytes
2108 * @return ClassDefiner that defines a hidden class of the given bytes.
2109 */
2110 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes) {
2111 return makeHiddenClassDefiner(name, bytes, Set.of(), false);
2112 }
2113
2114 /**
2115 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2116 * from the given bytes and options. No package name check on the given name.
2117 *
2118 * @param name the name of the class and the name in the class bytes is ignored.
2119 * @param bytes class bytes
2120 * @param options class options
2121 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2122 */
2123 ClassDefiner makeHiddenClassDefiner(String name,
2124 byte[] bytes,
2125 Set<ClassOption> options,
2126 boolean accessVmAnnotations) {
2127 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2128 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2129 // jdk.internal.vm.annotations are permitted for classes
2130 // defined to boot loader and platform loader
2131 flags |= ACCESS_VM_ANNOTATIONS;
2132 }
2133
2134 return new ClassDefiner(this, name, bytes, flags);
2135 }
2136
2137 static class ClassDefiner {
2138 private final Lookup lookup;
2139 private final String name;
2140 private final byte[] bytes;
2141 private final int classFlags;
2142
2143 private ClassDefiner(Lookup lookup, String name, byte[] bytes, int flags) {
2144 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2145 this.lookup = lookup;
2146 this.bytes = bytes;
2147 this.classFlags = flags;
2148 this.name = name;
2149 }
2150
2151 String className() {
2152 return name;
2153 }
2154
2155 Class<?> defineClass(boolean initialize) {
2156 return defineClass(initialize, null);
2157 }
2158
2159 Lookup defineClassAsLookup(boolean initialize) {
2160 Class<?> c = defineClass(initialize, null);
2161 return new Lookup(c, null, FULL_POWER_MODES);
2162 }
2163
2164 /**
2165 * Defines the class of the given bytes and the given classData.
2166 * If {@code initialize} parameter is true, then the class will be initialized.
2167 *
2168 * @param initialize true if the class to be initialized
2169 * @param classData classData or null
2170 * @return the class
2171 *
2172 * @throws LinkageError linkage error
2173 */
2174 Class<?> defineClass(boolean initialize, Object classData) {
2175 Class<?> lookupClass = lookup.lookupClass();
2176 ClassLoader loader = lookupClass.getClassLoader();
2177 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2178 Class<?> c = JLA.defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2179 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2180 return c;
2181 }
2182
2183 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2184 // initialize must be true if classData is non-null
2185 assert classData == null || initialize == true;
2186 Class<?> c = defineClass(initialize, classData);
2187 return new Lookup(c, null, FULL_POWER_MODES);
2188 }
2189
2190 private boolean isNestmate() {
2191 return (classFlags & NESTMATE_CLASS) != 0;
2192 }
2193 }
2194
2195 private ProtectionDomain lookupClassProtectionDomain() {
2196 ProtectionDomain pd = cachedProtectionDomain;
2197 if (pd == null) {
2198 cachedProtectionDomain = pd = JLA.protectionDomain(lookupClass);
2199 }
2200 return pd;
2201 }
2202
2203 // cached protection domain
2204 private volatile ProtectionDomain cachedProtectionDomain;
2205
2206 // Make sure outer class is initialized first.
2207 static { IMPL_NAMES.getClass(); }
2208
2209 /** Package-private version of lookup which is trusted. */
2210 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2211
2212 /** Version of lookup which is trusted minimally.
2213 * It can only be used to create method handles to publicly accessible
2214 * members in packages that are exported unconditionally.
2215 */
2216 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2217
2218 static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
2219
2220 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2221 String name = lookupClass.getName();
2222 if (name.startsWith("java.lang.invoke."))
2223 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2224 }
2225
2226 /**
2227 * Displays the name of the class from which lookups are to be made.
2228 * followed with "/" and the name of the {@linkplain #previousLookupClass()
2229 * previous lookup class} if present.
2230 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2231 * If there are restrictions on the access permitted to this lookup,
2232 * this is indicated by adding a suffix to the class name, consisting
2233 * of a slash and a keyword. The keyword represents the strongest
2234 * allowed access, and is chosen as follows:
2235 * <ul>
2236 * <li>If no access is allowed, the suffix is "/noaccess".
2237 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2238 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2239 * <li>If only public and module access are allowed, the suffix is "/module".
2240 * <li>If public and package access are allowed, the suffix is "/package".
2241 * <li>If public, package, and private access are allowed, the suffix is "/private".
2242 * </ul>
2243 * If none of the above cases apply, it is the case that full access
2244 * (public, module, package, private, and protected) is allowed.
2245 * In this case, no suffix is added.
2246 * This is true only of an object obtained originally from
2247 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2248 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2249 * always have restricted access, and will display a suffix.
2250 * <p>
2251 * (It may seem strange that protected access should be
2252 * stronger than private access. Viewed independently from
2253 * package access, protected access is the first to be lost,
2254 * because it requires a direct subclass relationship between
2255 * caller and callee.)
2256 * @see #in
2257 *
2258 * @revised 9
2259 * @spec JPMS
2260 */
2261 @Override
2262 public String toString() {
2263 String cname = lookupClass.getName();
2264 if (prevLookupClass != null)
2265 cname += "/" + prevLookupClass.getName();
2266 switch (allowedModes) {
2267 case 0: // no privileges
2268 return cname + "/noaccess";
2269 case UNCONDITIONAL:
2270 return cname + "/publicLookup";
2271 case PUBLIC:
2272 return cname + "/public";
2273 case PUBLIC|MODULE:
2274 return cname + "/module";
2275 case PUBLIC|PACKAGE:
2276 case PUBLIC|MODULE|PACKAGE:
2277 return cname + "/package";
2278 case FULL_POWER_MODES & (~PROTECTED):
2279 case FULL_POWER_MODES & ~(PROTECTED|MODULE):
2280 return cname + "/private";
2281 case FULL_POWER_MODES:
2282 case FULL_POWER_MODES & (~MODULE):
2283 return cname;
2284 case TRUSTED:
2285 return "/trusted"; // internal only; not exported
2286 default: // Should not happen, but it's a bitfield...
2287 cname = cname + "/" + Integer.toHexString(allowedModes);
2288 assert(false) : cname;
2289 return cname;
2290 }
2291 }
2292
2293 /**
2294 * Produces a method handle for a static method.
2295 * The type of the method handle will be that of the method.
2296 * (Since static methods do not take receivers, there is no
2297 * additional receiver argument inserted into the method handle type,
2298 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2299 * The method and all its argument types must be accessible to the lookup object.
2300 * <p>
2301 * The returned method handle will have
2302 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2303 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2304 * <p>
2305 * If the returned method handle is invoked, the method's class will
2306 * be initialized, if it has not already been initialized.
2307 * <p><b>Example:</b>
2308 * <blockquote><pre>{@code
2309 import static java.lang.invoke.MethodHandles.*;
2310 import static java.lang.invoke.MethodType.*;
2311 ...
2312 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2313 "asList", methodType(List.class, Object[].class));
2314 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2315 * }</pre></blockquote>
2316 * @param refc the class from which the method is accessed
2317 * @param name the name of the method
2318 * @param type the type of the method
2319 * @return the desired method handle
2320 * @throws NoSuchMethodException if the method does not exist
2321 * @throws IllegalAccessException if access checking fails,
2322 * or if the method is not {@code static},
2323 * or if the method's variable arity modifier bit
2324 * is set and {@code asVarargsCollector} fails
2325 * @throws SecurityException if a security manager is present and it
2326 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2327 * @throws NullPointerException if any argument is null
2328 */
2329 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2330 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2331 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2332 }
2333
2334 /**
2335 * Produces a method handle for a virtual method.
2336 * The type of the method handle will be that of the method,
2337 * with the receiver type (usually {@code refc}) prepended.
2338 * The method and all its argument types must be accessible to the lookup object.
2339 * <p>
2340 * When called, the handle will treat the first argument as a receiver
2341 * and, for non-private methods, dispatch on the receiver's type to determine which method
2342 * implementation to enter.
2343 * For private methods the named method in {@code refc} will be invoked on the receiver.
2344 * (The dispatching action is identical with that performed by an
2345 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2346 * <p>
2347 * The first argument will be of type {@code refc} if the lookup
2348 * class has full privileges to access the member. Otherwise
2349 * the member must be {@code protected} and the first argument
2350 * will be restricted in type to the lookup class.
2351 * <p>
2352 * The returned method handle will have
2353 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2354 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2355 * <p>
2356 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2357 * instructions and method handles produced by {@code findVirtual},
2358 * if the class is {@code MethodHandle} and the name string is
2359 * {@code invokeExact} or {@code invoke}, the resulting
2360 * method handle is equivalent to one produced by
2361 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2362 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2363 * with the same {@code type} argument.
2364 * <p>
2365 * If the class is {@code VarHandle} and the name string corresponds to
2366 * the name of a signature-polymorphic access mode method, the resulting
2367 * method handle is equivalent to one produced by
2368 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2369 * the access mode corresponding to the name string and with the same
2370 * {@code type} arguments.
2371 * <p>
2372 * <b>Example:</b>
2373 * <blockquote><pre>{@code
2374 import static java.lang.invoke.MethodHandles.*;
2375 import static java.lang.invoke.MethodType.*;
2376 ...
2377 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2378 "concat", methodType(String.class, String.class));
2379 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2380 "hashCode", methodType(int.class));
2381 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2382 "hashCode", methodType(int.class));
2383 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2384 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2385 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2386 // interface method:
2387 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2388 "subSequence", methodType(CharSequence.class, int.class, int.class));
2389 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2390 // constructor "internal method" must be accessed differently:
2391 MethodType MT_newString = methodType(void.class); //()V for new String()
2392 try { assertEquals("impossible", lookup()
2393 .findVirtual(String.class, "<init>", MT_newString));
2394 } catch (NoSuchMethodException ex) { } // OK
2395 MethodHandle MH_newString = publicLookup()
2396 .findConstructor(String.class, MT_newString);
2397 assertEquals("", (String) MH_newString.invokeExact());
2398 * }</pre></blockquote>
2399 *
2400 * @param refc the class or interface from which the method is accessed
2401 * @param name the name of the method
2402 * @param type the type of the method, with the receiver argument omitted
2403 * @return the desired method handle
2404 * @throws NoSuchMethodException if the method does not exist
2405 * @throws IllegalAccessException if access checking fails,
2406 * or if the method is {@code static},
2407 * or if the method's variable arity modifier bit
2408 * is set and {@code asVarargsCollector} fails
2409 * @throws SecurityException if a security manager is present and it
2410 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2411 * @throws NullPointerException if any argument is null
2412 */
2413 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2414 if (refc == MethodHandle.class) {
2415 MethodHandle mh = findVirtualForMH(name, type);
2416 if (mh != null) return mh;
2417 } else if (refc == VarHandle.class) {
2418 MethodHandle mh = findVirtualForVH(name, type);
2419 if (mh != null) return mh;
2420 }
2421 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2422 MemberName method = resolveOrFail(refKind, refc, name, type);
2423 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2424 }
2425 private MethodHandle findVirtualForMH(String name, MethodType type) {
2426 // these names require special lookups because of the implicit MethodType argument
2427 if ("invoke".equals(name))
2428 return invoker(type);
2429 if ("invokeExact".equals(name))
2430 return exactInvoker(type);
2431 assert(!MemberName.isMethodHandleInvokeName(name));
2432 return null;
2433 }
2434 private MethodHandle findVirtualForVH(String name, MethodType type) {
2435 try {
2436 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2437 } catch (IllegalArgumentException e) {
2438 return null;
2439 }
2440 }
2441
2442 /**
2443 * Produces a method handle which creates an object and initializes it, using
2444 * the constructor of the specified type.
2445 * The parameter types of the method handle will be those of the constructor,
2446 * while the return type will be a reference to the constructor's class.
2447 * The constructor and all its argument types must be accessible to the lookup object.
2448 * <p>
2449 * The requested type must have a return type of {@code void}.
2450 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2451 * <p>
2452 * The returned method handle will have
2453 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2454 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2455 * <p>
2456 * If the returned method handle is invoked, the constructor's class will
2457 * be initialized, if it has not already been initialized.
2458 * <p><b>Example:</b>
2459 * <blockquote><pre>{@code
2460 import static java.lang.invoke.MethodHandles.*;
2461 import static java.lang.invoke.MethodType.*;
2462 ...
2463 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2464 ArrayList.class, methodType(void.class, Collection.class));
2465 Collection orig = Arrays.asList("x", "y");
2466 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2467 assert(orig != copy);
2468 assertEquals(orig, copy);
2469 // a variable-arity constructor:
2470 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2471 ProcessBuilder.class, methodType(void.class, String[].class));
2472 ProcessBuilder pb = (ProcessBuilder)
2473 MH_newProcessBuilder.invoke("x", "y", "z");
2474 assertEquals("[x, y, z]", pb.command().toString());
2475 * }</pre></blockquote>
2476 * @param refc the class or interface from which the method is accessed
2477 * @param type the type of the method, with the receiver argument omitted, and a void return type
2478 * @return the desired method handle
2479 * @throws NoSuchMethodException if the constructor does not exist
2480 * @throws IllegalAccessException if access checking fails
2481 * or if the method's variable arity modifier bit
2482 * is set and {@code asVarargsCollector} fails
2483 * @throws SecurityException if a security manager is present and it
2484 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2485 * @throws NullPointerException if any argument is null
2486 */
2487 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2488 if (refc.isArray()) {
2489 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2490 }
2491 String name = "<init>";
2492 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2493 return getDirectConstructor(refc, ctor);
2494 }
2495
2496 /**
2497 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2498 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2499 * Such a resolution, as specified in JVMS 5.4.3.1 section, attempts to locate and load the class,
2500 * and then determines whether the class is accessible to this lookup object.
2501 * <p>
2502 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2503 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2504 *
2505 * @param targetName the fully qualified name of the class to be looked up.
2506 * @return the requested class.
2507 * @throws SecurityException if a security manager is present and it
2508 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2509 * @throws LinkageError if the linkage fails
2510 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2511 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2512 * modes.
2513 * @since 9
2514 * @jvms 5.4.3.1 Class and Interface Resolution
2515 */
2516 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2517 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2518 return accessClass(targetClass);
2519 }
2520
2521 /**
2522 * Determines if a class can be accessed from the lookup context defined by
2523 * this {@code Lookup} object. The static initializer of the class is not run.
2524 * <p>
2525 * If the {@code targetClass} is in the same module as the lookup class,
2526 * the lookup class is {@code LC} in module {@code M1} and
2527 * the previous lookup class is in module {@code M0} or
2528 * {@code null} if not present,
2529 * {@code targetClass} is accessible if and only if one of the following is true:
2530 * <ul>
2531 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2532 * {@code LC} or other class in the same nest of {@code LC}.</li>
2533 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2534 * in the same runtime package of {@code LC}.</li>
2535 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2536 * a public type in {@code M1}.</li>
2537 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2538 * a public type in a package exported by {@code M1} to at least {@code M0}
2539 * if the previous lookup class is present; otherwise, {@code targetClass}
2540 * is a public type in a package exported by {@code M1} unconditionally.</li>
2541 * </ul>
2542 *
2543 * <p>
2544 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2545 * can access public types in all modules when the type is in a package
2546 * that is exported unconditionally.
2547 * <p>
2548 * Otherwise, the target class is in a different module from {@code lookupClass},
2549 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2550 * is inaccessible.
2551 * <p>
2552 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2553 * {@code M1} is the module containing {@code lookupClass} and
2554 * {@code M2} is the module containing {@code targetClass},
2555 * then {@code targetClass} is accessible if and only if
2556 * <ul>
2557 * <li>{@code M1} reads {@code M2}, and
2558 * <li>{@code targetClass} is public and in a package exported by
2559 * {@code M2} at least to {@code M1}.
2560 * </ul>
2561 * <p>
2562 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2563 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2564 * containing the previous lookup class, then {@code targetClass} is accessible
2565 * if and only if one of the following is true:
2566 * <ul>
2567 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2568 * {@linkplain Module#reads reads} {@code M0} and the type is
2569 * in a package that is exported to at least {@code M1}.
2570 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2571 * {@linkplain Module#reads reads} {@code M1} and the type is
2572 * in a package that is exported to at least {@code M0}.
2573 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2574 * and {@code M1} reads {@code M2} and the type is in a package
2575 * that is exported to at least both {@code M0} and {@code M2}.
2576 * </ul>
2577 * <p>
2578 * Otherwise, {@code targetClass} is not accessible.
2579 *
2580 * @param targetClass the class to be access-checked
2581 * @return the class that has been access-checked
2582 * @throws IllegalAccessException if the class is not accessible from the lookup class
2583 * and previous lookup class, if present, using the allowed access modes.
2584 * @throws SecurityException if a security manager is present and it
2585 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2586 * @since 9
2587 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2588 */
2589 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2590 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2591 throw new MemberName(targetClass).makeAccessException("access violation", this);
2592 }
2593 checkSecurityManager(targetClass, null);
2594 return targetClass;
2595 }
2596
2597 /**
2598 * Produces an early-bound method handle for a virtual method.
2599 * It will bypass checks for overriding methods on the receiver,
2600 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2601 * instruction from within the explicitly specified {@code specialCaller}.
2602 * The type of the method handle will be that of the method,
2603 * with a suitably restricted receiver type prepended.
2604 * (The receiver type will be {@code specialCaller} or a subtype.)
2605 * The method and all its argument types must be accessible
2606 * to the lookup object.
2607 * <p>
2608 * Before method resolution,
2609 * if the explicitly specified caller class is not identical with the
2610 * lookup class, or if this lookup object does not have
2611 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2612 * privileges, the access fails.
2613 * <p>
2614 * The returned method handle will have
2615 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2616 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2617 * <p style="font-size:smaller;">
2618 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2619 * even though the {@code invokespecial} instruction can refer to them
2620 * in special circumstances. Use {@link #findConstructor findConstructor}
2621 * to access instance initialization methods in a safe manner.)</em>
2622 * <p><b>Example:</b>
2623 * <blockquote><pre>{@code
2624 import static java.lang.invoke.MethodHandles.*;
2625 import static java.lang.invoke.MethodType.*;
2626 ...
2627 static class Listie extends ArrayList {
2628 public String toString() { return "[wee Listie]"; }
2629 static Lookup lookup() { return MethodHandles.lookup(); }
2630 }
2631 ...
2632 // no access to constructor via invokeSpecial:
2633 MethodHandle MH_newListie = Listie.lookup()
2634 .findConstructor(Listie.class, methodType(void.class));
2635 Listie l = (Listie) MH_newListie.invokeExact();
2636 try { assertEquals("impossible", Listie.lookup().findSpecial(
2637 Listie.class, "<init>", methodType(void.class), Listie.class));
2638 } catch (NoSuchMethodException ex) { } // OK
2639 // access to super and self methods via invokeSpecial:
2640 MethodHandle MH_super = Listie.lookup().findSpecial(
2641 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2642 MethodHandle MH_this = Listie.lookup().findSpecial(
2643 Listie.class, "toString" , methodType(String.class), Listie.class);
2644 MethodHandle MH_duper = Listie.lookup().findSpecial(
2645 Object.class, "toString" , methodType(String.class), Listie.class);
2646 assertEquals("[]", (String) MH_super.invokeExact(l));
2647 assertEquals(""+l, (String) MH_this.invokeExact(l));
2648 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2649 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2650 String.class, "toString", methodType(String.class), Listie.class));
2651 } catch (IllegalAccessException ex) { } // OK
2652 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2653 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2654 * }</pre></blockquote>
2655 *
2656 * @param refc the class or interface from which the method is accessed
2657 * @param name the name of the method (which must not be "<init>")
2658 * @param type the type of the method, with the receiver argument omitted
2659 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2660 * @return the desired method handle
2661 * @throws NoSuchMethodException if the method does not exist
2662 * @throws IllegalAccessException if access checking fails,
2663 * or if the method is {@code static},
2664 * or if the method's variable arity modifier bit
2665 * is set and {@code asVarargsCollector} fails
2666 * @throws SecurityException if a security manager is present and it
2667 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2668 * @throws NullPointerException if any argument is null
2669 */
2670 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2671 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2672 checkSpecialCaller(specialCaller, refc);
2673 Lookup specialLookup = this.in(specialCaller);
2674 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2675 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
2676 }
2677
2678 /**
2679 * Produces a method handle giving read access to a non-static field.
2680 * The type of the method handle will have a return type of the field's
2681 * value type.
2682 * The method handle's single argument will be the instance containing
2683 * the field.
2684 * Access checking is performed immediately on behalf of the lookup class.
2685 * @param refc the class or interface from which the method is accessed
2686 * @param name the field's name
2687 * @param type the field's type
2688 * @return a method handle which can load values from the field
2689 * @throws NoSuchFieldException if the field does not exist
2690 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2691 * @throws SecurityException if a security manager is present and it
2692 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2693 * @throws NullPointerException if any argument is null
2694 * @see #findVarHandle(Class, String, Class)
2695 */
2696 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2697 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2698 return getDirectField(REF_getField, refc, field);
2699 }
2700
2701 /**
2702 * Produces a method handle giving write access to a non-static field.
2703 * The type of the method handle will have a void return type.
2704 * The method handle will take two arguments, the instance containing
2705 * the field, and the value to be stored.
2706 * The second argument will be of the field's value type.
2707 * Access checking is performed immediately on behalf of the lookup class.
2708 * @param refc the class or interface from which the method is accessed
2709 * @param name the field's name
2710 * @param type the field's type
2711 * @return a method handle which can store values into the field
2712 * @throws NoSuchFieldException if the field does not exist
2713 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2714 * or {@code final}
2715 * @throws SecurityException if a security manager is present and it
2716 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2717 * @throws NullPointerException if any argument is null
2718 * @see #findVarHandle(Class, String, Class)
2719 */
2720 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2721 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2722 return getDirectField(REF_putField, refc, field);
2723 }
2724
2725 /**
2726 * Produces a VarHandle giving access to a non-static field {@code name}
2727 * of type {@code type} declared in a class of type {@code recv}.
2728 * The VarHandle's variable type is {@code type} and it has one
2729 * coordinate type, {@code recv}.
2730 * <p>
2731 * Access checking is performed immediately on behalf of the lookup
2732 * class.
2733 * <p>
2734 * Certain access modes of the returned VarHandle are unsupported under
2735 * the following conditions:
2736 * <ul>
2737 * <li>if the field is declared {@code final}, then the write, atomic
2738 * update, numeric atomic update, and bitwise atomic update access
2739 * modes are unsupported.
2740 * <li>if the field type is anything other than {@code byte},
2741 * {@code short}, {@code char}, {@code int}, {@code long},
2742 * {@code float}, or {@code double} then numeric atomic update
2743 * access modes are unsupported.
2744 * <li>if the field type is anything other than {@code boolean},
2745 * {@code byte}, {@code short}, {@code char}, {@code int} or
2746 * {@code long} then bitwise atomic update access modes are
2747 * unsupported.
2748 * </ul>
2749 * <p>
2750 * If the field is declared {@code volatile} then the returned VarHandle
2751 * will override access to the field (effectively ignore the
2752 * {@code volatile} declaration) in accordance to its specified
2753 * access modes.
2754 * <p>
2755 * If the field type is {@code float} or {@code double} then numeric
2756 * and atomic update access modes compare values using their bitwise
2757 * representation (see {@link Float#floatToRawIntBits} and
2758 * {@link Double#doubleToRawLongBits}, respectively).
2759 * @apiNote
2760 * Bitwise comparison of {@code float} values or {@code double} values,
2761 * as performed by the numeric and atomic update access modes, differ
2762 * from the primitive {@code ==} operator and the {@link Float#equals}
2763 * and {@link Double#equals} methods, specifically with respect to
2764 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2765 * Care should be taken when performing a compare and set or a compare
2766 * and exchange operation with such values since the operation may
2767 * unexpectedly fail.
2768 * There are many possible NaN values that are considered to be
2769 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2770 * provided by Java can distinguish between them. Operation failure can
2771 * occur if the expected or witness value is a NaN value and it is
2772 * transformed (perhaps in a platform specific manner) into another NaN
2773 * value, and thus has a different bitwise representation (see
2774 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2775 * details).
2776 * The values {@code -0.0} and {@code +0.0} have different bitwise
2777 * representations but are considered equal when using the primitive
2778 * {@code ==} operator. Operation failure can occur if, for example, a
2779 * numeric algorithm computes an expected value to be say {@code -0.0}
2780 * and previously computed the witness value to be say {@code +0.0}.
2781 * @param recv the receiver class, of type {@code R}, that declares the
2782 * non-static field
2783 * @param name the field's name
2784 * @param type the field's type, of type {@code T}
2785 * @return a VarHandle giving access to non-static fields.
2786 * @throws NoSuchFieldException if the field does not exist
2787 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2788 * @throws SecurityException if a security manager is present and it
2789 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2790 * @throws NullPointerException if any argument is null
2791 * @since 9
2792 */
2793 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2794 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
2795 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
2796 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
2797 }
2798
2799 /**
2800 * Produces a method handle giving read access to a static field.
2801 * The type of the method handle will have a return type of the field's
2802 * value type.
2803 * The method handle will take no arguments.
2804 * Access checking is performed immediately on behalf of the lookup class.
2805 * <p>
2806 * If the returned method handle is invoked, the field's class will
2807 * be initialized, if it has not already been initialized.
2808 * @param refc the class or interface from which the method is accessed
2809 * @param name the field's name
2810 * @param type the field's type
2811 * @return a method handle which can load values from the field
2812 * @throws NoSuchFieldException if the field does not exist
2813 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2814 * @throws SecurityException if a security manager is present and it
2815 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2816 * @throws NullPointerException if any argument is null
2817 */
2818 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2819 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
2820 return getDirectField(REF_getStatic, refc, field);
2821 }
2822
2823 /**
2824 * Produces a method handle giving write access to a static field.
2825 * The type of the method handle will have a void return type.
2826 * The method handle will take a single
2827 * argument, of the field's value type, the value to be stored.
2828 * Access checking is performed immediately on behalf of the lookup class.
2829 * <p>
2830 * If the returned method handle is invoked, the field's class will
2831 * be initialized, if it has not already been initialized.
2832 * @param refc the class or interface from which the method is accessed
2833 * @param name the field's name
2834 * @param type the field's type
2835 * @return a method handle which can store values into the field
2836 * @throws NoSuchFieldException if the field does not exist
2837 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2838 * or is {@code final}
2839 * @throws SecurityException if a security manager is present and it
2840 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2841 * @throws NullPointerException if any argument is null
2842 */
2843 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2844 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
2845 return getDirectField(REF_putStatic, refc, field);
2846 }
2847
2848 /**
2849 * Produces a VarHandle giving access to a static field {@code name} of
2850 * type {@code type} declared in a class of type {@code decl}.
2851 * The VarHandle's variable type is {@code type} and it has no
2852 * coordinate types.
2853 * <p>
2854 * Access checking is performed immediately on behalf of the lookup
2855 * class.
2856 * <p>
2857 * If the returned VarHandle is operated on, the declaring class will be
2858 * initialized, if it has not already been initialized.
2859 * <p>
2860 * Certain access modes of the returned VarHandle are unsupported under
2861 * the following conditions:
2862 * <ul>
2863 * <li>if the field is declared {@code final}, then the write, atomic
2864 * update, numeric atomic update, and bitwise atomic update access
2865 * modes are unsupported.
2866 * <li>if the field type is anything other than {@code byte},
2867 * {@code short}, {@code char}, {@code int}, {@code long},
2868 * {@code float}, or {@code double}, then numeric atomic update
2869 * access modes are unsupported.
2870 * <li>if the field type is anything other than {@code boolean},
2871 * {@code byte}, {@code short}, {@code char}, {@code int} or
2872 * {@code long} then bitwise atomic update access modes are
2873 * unsupported.
2874 * </ul>
2875 * <p>
2876 * If the field is declared {@code volatile} then the returned VarHandle
2877 * will override access to the field (effectively ignore the
2878 * {@code volatile} declaration) in accordance to its specified
2879 * access modes.
2880 * <p>
2881 * If the field type is {@code float} or {@code double} then numeric
2882 * and atomic update access modes compare values using their bitwise
2883 * representation (see {@link Float#floatToRawIntBits} and
2884 * {@link Double#doubleToRawLongBits}, respectively).
2885 * @apiNote
2886 * Bitwise comparison of {@code float} values or {@code double} values,
2887 * as performed by the numeric and atomic update access modes, differ
2888 * from the primitive {@code ==} operator and the {@link Float#equals}
2889 * and {@link Double#equals} methods, specifically with respect to
2890 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2891 * Care should be taken when performing a compare and set or a compare
2892 * and exchange operation with such values since the operation may
2893 * unexpectedly fail.
2894 * There are many possible NaN values that are considered to be
2895 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2896 * provided by Java can distinguish between them. Operation failure can
2897 * occur if the expected or witness value is a NaN value and it is
2898 * transformed (perhaps in a platform specific manner) into another NaN
2899 * value, and thus has a different bitwise representation (see
2900 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2901 * details).
2902 * The values {@code -0.0} and {@code +0.0} have different bitwise
2903 * representations but are considered equal when using the primitive
2904 * {@code ==} operator. Operation failure can occur if, for example, a
2905 * numeric algorithm computes an expected value to be say {@code -0.0}
2906 * and previously computed the witness value to be say {@code +0.0}.
2907 * @param decl the class that declares the static field
2908 * @param name the field's name
2909 * @param type the field's type, of type {@code T}
2910 * @return a VarHandle giving access to a static field
2911 * @throws NoSuchFieldException if the field does not exist
2912 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2913 * @throws SecurityException if a security manager is present and it
2914 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2915 * @throws NullPointerException if any argument is null
2916 * @since 9
2917 */
2918 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2919 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
2920 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
2921 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
2922 }
2923
2924 /**
2925 * Produces an early-bound method handle for a non-static method.
2926 * The receiver must have a supertype {@code defc} in which a method
2927 * of the given name and type is accessible to the lookup class.
2928 * The method and all its argument types must be accessible to the lookup object.
2929 * The type of the method handle will be that of the method,
2930 * without any insertion of an additional receiver parameter.
2931 * The given receiver will be bound into the method handle,
2932 * so that every call to the method handle will invoke the
2933 * requested method on the given receiver.
2934 * <p>
2935 * The returned method handle will have
2936 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2937 * the method's variable arity modifier bit ({@code 0x0080}) is set
2938 * <em>and</em> the trailing array argument is not the only argument.
2939 * (If the trailing array argument is the only argument,
2940 * the given receiver value will be bound to it.)
2941 * <p>
2942 * This is almost equivalent to the following code, with some differences noted below:
2943 * <blockquote><pre>{@code
2944 import static java.lang.invoke.MethodHandles.*;
2945 import static java.lang.invoke.MethodType.*;
2946 ...
2947 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
2948 MethodHandle mh1 = mh0.bindTo(receiver);
2949 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
2950 return mh1;
2951 * }</pre></blockquote>
2952 * where {@code defc} is either {@code receiver.getClass()} or a super
2953 * type of that class, in which the requested method is accessible
2954 * to the lookup class.
2955 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
2956 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
2957 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
2958 * the receiver is restricted by {@code findVirtual} to the lookup class.)
2959 * @param receiver the object from which the method is accessed
2960 * @param name the name of the method
2961 * @param type the type of the method, with the receiver argument omitted
2962 * @return the desired method handle
2963 * @throws NoSuchMethodException if the method does not exist
2964 * @throws IllegalAccessException if access checking fails
2965 * or if the method's variable arity modifier bit
2966 * is set and {@code asVarargsCollector} fails
2967 * @throws SecurityException if a security manager is present and it
2968 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2969 * @throws NullPointerException if any argument is null
2970 * @see MethodHandle#bindTo
2971 * @see #findVirtual
2972 */
2973 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2974 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2975 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2976 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
2977 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2978 throw new IllegalAccessException("The restricted defining class " +
2979 mh.type().leadingReferenceParameter().getName() +
2980 " is not assignable from receiver class " +
2981 receiver.getClass().getName());
2982 }
2983 return mh.bindArgumentL(0, receiver).setVarargs(method);
2984 }
2985
2986 /**
2987 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2988 * to <i>m</i>, if the lookup class has permission.
2989 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2990 * If <i>m</i> is virtual, overriding is respected on every call.
2991 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2992 * The type of the method handle will be that of the method,
2993 * with the receiver type prepended (but only if it is non-static).
2994 * If the method's {@code accessible} flag is not set,
2995 * access checking is performed immediately on behalf of the lookup class.
2996 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2997 * <p>
2998 * The returned method handle will have
2999 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3000 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3001 * <p>
3002 * If <i>m</i> is static, and
3003 * if the returned method handle is invoked, the method's class will
3004 * be initialized, if it has not already been initialized.
3005 * @param m the reflected method
3006 * @return a method handle which can invoke the reflected method
3007 * @throws IllegalAccessException if access checking fails
3008 * or if the method's variable arity modifier bit
3009 * is set and {@code asVarargsCollector} fails
3010 * @throws NullPointerException if the argument is null
3011 */
3012 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3013 if (m.getDeclaringClass() == MethodHandle.class) {
3014 MethodHandle mh = unreflectForMH(m);
3015 if (mh != null) return mh;
3016 }
3017 if (m.getDeclaringClass() == VarHandle.class) {
3018 MethodHandle mh = unreflectForVH(m);
3019 if (mh != null) return mh;
3020 }
3021 MemberName method = new MemberName(m);
3022 byte refKind = method.getReferenceKind();
3023 if (refKind == REF_invokeSpecial)
3024 refKind = REF_invokeVirtual;
3025 assert(method.isMethod());
3026 @SuppressWarnings("deprecation")
3027 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3028 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3029 }
3030 private MethodHandle unreflectForMH(Method m) {
3031 // these names require special lookups because they throw UnsupportedOperationException
3032 if (MemberName.isMethodHandleInvokeName(m.getName()))
3033 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3034 return null;
3035 }
3036 private MethodHandle unreflectForVH(Method m) {
3037 // these names require special lookups because they throw UnsupportedOperationException
3038 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3039 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3040 return null;
3041 }
3042
3043 /**
3044 * Produces a method handle for a reflected method.
3045 * It will bypass checks for overriding methods on the receiver,
3046 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3047 * instruction from within the explicitly specified {@code specialCaller}.
3048 * The type of the method handle will be that of the method,
3049 * with a suitably restricted receiver type prepended.
3050 * (The receiver type will be {@code specialCaller} or a subtype.)
3051 * If the method's {@code accessible} flag is not set,
3052 * access checking is performed immediately on behalf of the lookup class,
3053 * as if {@code invokespecial} instruction were being linked.
3054 * <p>
3055 * Before method resolution,
3056 * if the explicitly specified caller class is not identical with the
3057 * lookup class, or if this lookup object does not have
3058 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3059 * privileges, the access fails.
3060 * <p>
3061 * The returned method handle will have
3062 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3063 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3064 * @param m the reflected method
3065 * @param specialCaller the class nominally calling the method
3066 * @return a method handle which can invoke the reflected method
3067 * @throws IllegalAccessException if access checking fails,
3068 * or if the method is {@code static},
3069 * or if the method's variable arity modifier bit
3070 * is set and {@code asVarargsCollector} fails
3071 * @throws NullPointerException if any argument is null
3072 */
3073 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3074 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3075 Lookup specialLookup = this.in(specialCaller);
3076 MemberName method = new MemberName(m, true);
3077 assert(method.isMethod());
3078 // ignore m.isAccessible: this is a new kind of access
3079 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3080 }
3081
3082 /**
3083 * Produces a method handle for a reflected constructor.
3084 * The type of the method handle will be that of the constructor,
3085 * with the return type changed to the declaring class.
3086 * The method handle will perform a {@code newInstance} operation,
3087 * creating a new instance of the constructor's class on the
3088 * arguments passed to the method handle.
3089 * <p>
3090 * If the constructor's {@code accessible} flag is not set,
3091 * access checking is performed immediately on behalf of the lookup class.
3092 * <p>
3093 * The returned method handle will have
3094 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3095 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3096 * <p>
3097 * If the returned method handle is invoked, the constructor's class will
3098 * be initialized, if it has not already been initialized.
3099 * @param c the reflected constructor
3100 * @return a method handle which can invoke the reflected constructor
3101 * @throws IllegalAccessException if access checking fails
3102 * or if the method's variable arity modifier bit
3103 * is set and {@code asVarargsCollector} fails
3104 * @throws NullPointerException if the argument is null
3105 */
3106 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3107 MemberName ctor = new MemberName(c);
3108 assert(ctor.isConstructor());
3109 @SuppressWarnings("deprecation")
3110 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3111 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3112 }
3113
3114 /**
3115 * Produces a method handle giving read access to a reflected field.
3116 * The type of the method handle will have a return type of the field's
3117 * value type.
3118 * If the field is {@code static}, the method handle will take no arguments.
3119 * Otherwise, its single argument will be the instance containing
3120 * the field.
3121 * If the {@code Field} object's {@code accessible} flag is not set,
3122 * access checking is performed immediately on behalf of the lookup class.
3123 * <p>
3124 * If the field is static, and
3125 * if the returned method handle is invoked, the field's class will
3126 * be initialized, if it has not already been initialized.
3127 * @param f the reflected field
3128 * @return a method handle which can load values from the reflected field
3129 * @throws IllegalAccessException if access checking fails
3130 * @throws NullPointerException if the argument is null
3131 */
3132 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3133 return unreflectField(f, false);
3134 }
3135
3136 /**
3137 * Produces a method handle giving write access to a reflected field.
3138 * The type of the method handle will have a void return type.
3139 * If the field is {@code static}, the method handle will take a single
3140 * argument, of the field's value type, the value to be stored.
3141 * Otherwise, the two arguments will be the instance containing
3142 * the field, and the value to be stored.
3143 * If the {@code Field} object's {@code accessible} flag is not set,
3144 * access checking is performed immediately on behalf of the lookup class.
3145 * <p>
3146 * If the field is {@code final}, write access will not be
3147 * allowed and access checking will fail, except under certain
3148 * narrow circumstances documented for {@link Field#set Field.set}.
3149 * A method handle is returned only if a corresponding call to
3150 * the {@code Field} object's {@code set} method could return
3151 * normally. In particular, fields which are both {@code static}
3152 * and {@code final} may never be set.
3153 * <p>
3154 * If the field is {@code static}, and
3155 * if the returned method handle is invoked, the field's class will
3156 * be initialized, if it has not already been initialized.
3157 * @param f the reflected field
3158 * @return a method handle which can store values into the reflected field
3159 * @throws IllegalAccessException if access checking fails,
3160 * or if the field is {@code final} and write access
3161 * is not enabled on the {@code Field} object
3162 * @throws NullPointerException if the argument is null
3163 */
3164 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3165 return unreflectField(f, true);
3166 }
3167
3168 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3169 MemberName field = new MemberName(f, isSetter);
3170 if (isSetter && field.isFinal()) {
3171 if (field.isStatic()) {
3172 throw field.makeAccessException("static final field has no write access", this);
3173 } else if (field.getDeclaringClass().isHidden()){
3174 throw field.makeAccessException("final field in a hidden class has no write access", this);
3175 }
3176 }
3177 assert(isSetter
3178 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3179 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3180 @SuppressWarnings("deprecation")
3181 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3182 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3183 }
3184
3185 /**
3186 * Produces a VarHandle giving access to a reflected field {@code f}
3187 * of type {@code T} declared in a class of type {@code R}.
3188 * The VarHandle's variable type is {@code T}.
3189 * If the field is non-static the VarHandle has one coordinate type,
3190 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3191 * coordinate types.
3192 * <p>
3193 * Access checking is performed immediately on behalf of the lookup
3194 * class, regardless of the value of the field's {@code accessible}
3195 * flag.
3196 * <p>
3197 * If the field is static, and if the returned VarHandle is operated
3198 * on, the field's declaring class will be initialized, if it has not
3199 * already been initialized.
3200 * <p>
3201 * Certain access modes of the returned VarHandle are unsupported under
3202 * the following conditions:
3203 * <ul>
3204 * <li>if the field is declared {@code final}, then the write, atomic
3205 * update, numeric atomic update, and bitwise atomic update access
3206 * modes are unsupported.
3207 * <li>if the field type is anything other than {@code byte},
3208 * {@code short}, {@code char}, {@code int}, {@code long},
3209 * {@code float}, or {@code double} then numeric atomic update
3210 * access modes are unsupported.
3211 * <li>if the field type is anything other than {@code boolean},
3212 * {@code byte}, {@code short}, {@code char}, {@code int} or
3213 * {@code long} then bitwise atomic update access modes are
3214 * unsupported.
3215 * </ul>
3216 * <p>
3217 * If the field is declared {@code volatile} then the returned VarHandle
3218 * will override access to the field (effectively ignore the
3219 * {@code volatile} declaration) in accordance to its specified
3220 * access modes.
3221 * <p>
3222 * If the field type is {@code float} or {@code double} then numeric
3223 * and atomic update access modes compare values using their bitwise
3224 * representation (see {@link Float#floatToRawIntBits} and
3225 * {@link Double#doubleToRawLongBits}, respectively).
3226 * @apiNote
3227 * Bitwise comparison of {@code float} values or {@code double} values,
3228 * as performed by the numeric and atomic update access modes, differ
3229 * from the primitive {@code ==} operator and the {@link Float#equals}
3230 * and {@link Double#equals} methods, specifically with respect to
3231 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3232 * Care should be taken when performing a compare and set or a compare
3233 * and exchange operation with such values since the operation may
3234 * unexpectedly fail.
3235 * There are many possible NaN values that are considered to be
3236 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3237 * provided by Java can distinguish between them. Operation failure can
3238 * occur if the expected or witness value is a NaN value and it is
3239 * transformed (perhaps in a platform specific manner) into another NaN
3240 * value, and thus has a different bitwise representation (see
3241 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3242 * details).
3243 * The values {@code -0.0} and {@code +0.0} have different bitwise
3244 * representations but are considered equal when using the primitive
3245 * {@code ==} operator. Operation failure can occur if, for example, a
3246 * numeric algorithm computes an expected value to be say {@code -0.0}
3247 * and previously computed the witness value to be say {@code +0.0}.
3248 * @param f the reflected field, with a field of type {@code T}, and
3249 * a declaring class of type {@code R}
3250 * @return a VarHandle giving access to non-static fields or a static
3251 * field
3252 * @throws IllegalAccessException if access checking fails
3253 * @throws NullPointerException if the argument is null
3254 * @since 9
3255 */
3256 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3257 MemberName getField = new MemberName(f, false);
3258 MemberName putField = new MemberName(f, true);
3259 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3260 f.getDeclaringClass(), getField, putField);
3261 }
3262
3263 /**
3264 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3265 * created by this lookup object or a similar one.
3266 * Security and access checks are performed to ensure that this lookup object
3267 * is capable of reproducing the target method handle.
3268 * This means that the cracking may fail if target is a direct method handle
3269 * but was created by an unrelated lookup object.
3270 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3271 * and was created by a lookup object for a different class.
3272 * @param target a direct method handle to crack into symbolic reference components
3273 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3274 * @throws SecurityException if a security manager is present and it
3275 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3276 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3277 * @throws NullPointerException if the target is {@code null}
3278 * @see MethodHandleInfo
3279 * @since 1.8
3280 */
3281 public MethodHandleInfo revealDirect(MethodHandle target) {
3282 MemberName member = target.internalMemberName();
3283 if (member == null || (!member.isResolved() &&
3284 !member.isMethodHandleInvoke() &&
3285 !member.isVarHandleMethodInvoke()))
3286 throw newIllegalArgumentException("not a direct method handle");
3287 Class<?> defc = member.getDeclaringClass();
3288 byte refKind = member.getReferenceKind();
3289 assert(MethodHandleNatives.refKindIsValid(refKind));
3290 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3291 // Devirtualized method invocation is usually formally virtual.
3292 // To avoid creating extra MemberName objects for this common case,
3293 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3294 refKind = REF_invokeVirtual;
3295 if (refKind == REF_invokeVirtual && defc.isInterface())
3296 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3297 refKind = REF_invokeInterface;
3298 // Check SM permissions and member access before cracking.
3299 try {
3300 checkAccess(refKind, defc, member);
3301 checkSecurityManager(defc, member);
3302 } catch (IllegalAccessException ex) {
3303 throw new IllegalArgumentException(ex);
3304 }
3305 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3306 Class<?> callerClass = target.internalCallerClass();
3307 if (!hasFullPrivilegeAccess() || callerClass != lookupClass())
3308 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3309 }
3310 // Produce the handle to the results.
3311 return new InfoFromMemberName(this, member, refKind);
3312 }
3313
3314 /// Helper methods, all package-private.
3315
3316 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3317 checkSymbolicClass(refc); // do this before attempting to resolve
3318 Objects.requireNonNull(name);
3319 Objects.requireNonNull(type);
3320 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
3321 NoSuchFieldException.class);
3322 }
3323
3324 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3325 checkSymbolicClass(refc); // do this before attempting to resolve
3326 Objects.requireNonNull(name);
3327 Objects.requireNonNull(type);
3328 checkMethodName(refKind, name); // NPE check on name
3329 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
3330 NoSuchMethodException.class);
3331 }
3332
3333 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3334 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3335 Objects.requireNonNull(member.getName());
3336 Objects.requireNonNull(member.getType());
3337 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
3338 ReflectiveOperationException.class);
3339 }
3340
3341 MemberName resolveOrNull(byte refKind, MemberName member) {
3342 // do this before attempting to resolve
3343 if (!isClassAccessible(member.getDeclaringClass())) {
3344 return null;
3345 }
3346 Objects.requireNonNull(member.getName());
3347 Objects.requireNonNull(member.getType());
3348 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
3349 }
3350
3351 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3352 if (!isClassAccessible(refc)) {
3353 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3354 }
3355 }
3356
3357 boolean isClassAccessible(Class<?> refc) {
3358 Objects.requireNonNull(refc);
3359 Class<?> caller = lookupClassOrNull();
3360 return caller == null || VerifyAccess.isClassAccessible(refc, caller, prevLookupClass, allowedModes);
3361 }
3362
3363 /** Check name for an illegal leading "<" character. */
3364 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3365 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3366 throw new NoSuchMethodException("illegal method name: "+name);
3367 }
3368
3369
3370 /**
3371 * Find my trustable caller class if m is a caller sensitive method.
3372 * If this lookup object has full privilege access, then the caller class is the lookupClass.
3373 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3374 */
3375 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3376 if (MethodHandleNatives.isCallerSensitive(m) && !hasFullPrivilegeAccess()) {
3377 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3378 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3379 }
3380 return this;
3381 }
3382
3383 /**
3384 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3385 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3386 *
3387 * @deprecated This method was originally designed to test {@code PRIVATE} access
3388 * that implies full privilege access but {@code MODULE} access has since become
3389 * independent of {@code PRIVATE} access. It is recommended to call
3390 * {@link #hasFullPrivilegeAccess()} instead.
3391 * @since 9
3392 */
3393 @Deprecated(since="14")
3394 public boolean hasPrivateAccess() {
3395 return hasFullPrivilegeAccess();
3396 }
3397
3398 /**
3399 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3400 * i.e. {@code PRIVATE} and {@code MODULE} access.
3401 * A {@code Lookup} object must have full privilege access in order to
3402 * access all members that are allowed to the {@linkplain #lookupClass() lookup class}.
3403 *
3404 * @return {@code true} if this lookup has full privilege access.
3405 * @since 14
3406 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3407 */
3408 public boolean hasFullPrivilegeAccess() {
3409 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3410 }
3411
3412 /**
3413 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3414 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3415 * If this lookup object has full privilege access, then the caller class is the lookupClass.
3416 */
3417 void checkSecurityManager(Class<?> refc, MemberName m) {
3418 if (allowedModes == TRUSTED) return;
3419
3420 SecurityManager smgr = System.getSecurityManager();
3421 if (smgr == null) return;
3422
3423 // Step 1:
3424 boolean fullPowerLookup = hasFullPrivilegeAccess();
3425 if (!fullPowerLookup ||
3426 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3427 ReflectUtil.checkPackageAccess(refc);
3428 }
3429
3430 if (m == null) { // findClass or accessClass
3431 // Step 2b:
3432 if (!fullPowerLookup) {
3433 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3434 }
3435 return;
3436 }
3437
3438 // Step 2a:
3439 if (m.isPublic()) return;
3440 if (!fullPowerLookup) {
3441 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3442 }
3443
3444 // Step 3:
3445 Class<?> defc = m.getDeclaringClass();
3446 if (!fullPowerLookup && defc != refc) {
3447 ReflectUtil.checkPackageAccess(defc);
3448 }
3449 }
3450
3451 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3452 boolean wantStatic = (refKind == REF_invokeStatic);
3453 String message;
3454 if (m.isConstructor())
3455 message = "expected a method, not a constructor";
3456 else if (!m.isMethod())
3457 message = "expected a method";
3458 else if (wantStatic != m.isStatic())
3459 message = wantStatic ? "expected a static method" : "expected a non-static method";
3460 else
3461 { checkAccess(refKind, refc, m); return; }
3462 throw m.makeAccessException(message, this);
3463 }
3464
3465 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3466 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3467 String message;
3468 if (wantStatic != m.isStatic())
3469 message = wantStatic ? "expected a static field" : "expected a non-static field";
3470 else
3471 { checkAccess(refKind, refc, m); return; }
3472 throw m.makeAccessException(message, this);
3473 }
3474
3475 /** Check public/protected/private bits on the symbolic reference class and its member. */
3476 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3477 assert(m.referenceKindIsConsistentWith(refKind) &&
3478 MethodHandleNatives.refKindIsValid(refKind) &&
3479 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3480 int allowedModes = this.allowedModes;
3481 if (allowedModes == TRUSTED) return;
3482 int mods = m.getModifiers();
3483 if (Modifier.isProtected(mods) &&
3484 refKind == REF_invokeVirtual &&
3485 m.getDeclaringClass() == Object.class &&
3486 m.getName().equals("clone") &&
3487 refc.isArray()) {
3488 // The JVM does this hack also.
3489 // (See ClassVerifier::verify_invoke_instructions
3490 // and LinkResolver::check_method_accessability.)
3491 // Because the JVM does not allow separate methods on array types,
3492 // there is no separate method for int[].clone.
3493 // All arrays simply inherit Object.clone.
3494 // But for access checking logic, we make Object.clone
3495 // (normally protected) appear to be public.
3496 // Later on, when the DirectMethodHandle is created,
3497 // its leading argument will be restricted to the
3498 // requested array type.
3499 // N.B. The return type is not adjusted, because
3500 // that is *not* the bytecode behavior.
3501 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3502 }
3503 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3504 // cannot "new" a protected ctor in a different package
3505 mods ^= Modifier.PROTECTED;
3506 }
3507 if (Modifier.isFinal(mods) &&
3508 MethodHandleNatives.refKindIsSetter(refKind))
3509 throw m.makeAccessException("unexpected set of a final field", this);
3510 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3511 if ((requestedModes & allowedModes) != 0) {
3512 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3513 mods, lookupClass(), previousLookupClass(), allowedModes))
3514 return;
3515 } else {
3516 // Protected members can also be checked as if they were package-private.
3517 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3518 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3519 return;
3520 }
3521 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3522 }
3523
3524 String accessFailedMessage(Class<?> refc, MemberName m) {
3525 Class<?> defc = m.getDeclaringClass();
3526 int mods = m.getModifiers();
3527 // check the class first:
3528 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3529 (defc == refc ||
3530 Modifier.isPublic(refc.getModifiers())));
3531 if (!classOK && (allowedModes & PACKAGE) != 0) {
3532 // ignore previous lookup class to check if default package access
3533 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3534 (defc == refc ||
3535 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3536 }
3537 if (!classOK)
3538 return "class is not public";
3539 if (Modifier.isPublic(mods))
3540 return "access to public member failed"; // (how?, module not readable?)
3541 if (Modifier.isPrivate(mods))
3542 return "member is private";
3543 if (Modifier.isProtected(mods))
3544 return "member is protected";
3545 return "member is private to package";
3546 }
3547
3548 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3549 int allowedModes = this.allowedModes;
3550 if (allowedModes == TRUSTED) return;
3551 if ((lookupModes() & PRIVATE) == 0
3552 || (specialCaller != lookupClass()
3553 // ensure non-abstract methods in superinterfaces can be special-invoked
3554 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3555 throw new MemberName(specialCaller).
3556 makeAccessException("no private access for invokespecial", this);
3557 }
3558
3559 private boolean restrictProtectedReceiver(MemberName method) {
3560 // The accessing class only has the right to use a protected member
3561 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3562 if (!method.isProtected() || method.isStatic()
3563 || allowedModes == TRUSTED
3564 || method.getDeclaringClass() == lookupClass()
3565 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3566 return false;
3567 return true;
3568 }
3569 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3570 assert(!method.isStatic());
3571 // receiver type of mh is too wide; narrow to caller
3572 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3573 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3574 }
3575 MethodType rawType = mh.type();
3576 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3577 MethodType narrowType = rawType.changeParameterType(0, caller);
3578 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3579 assert(mh.viewAsTypeChecks(narrowType, true));
3580 return mh.copyWith(narrowType, mh.form);
3581 }
3582
3583 /** Check access and get the requested method. */
3584 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3585 final boolean doRestrict = true;
3586 final boolean checkSecurity = true;
3587 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3588 }
3589 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3590 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3591 final boolean doRestrict = false;
3592 final boolean checkSecurity = true;
3593 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
3594 }
3595 /** Check access and get the requested method, eliding security manager checks. */
3596 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3597 final boolean doRestrict = true;
3598 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3599 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3600 }
3601 /** Common code for all methods; do not call directly except from immediately above. */
3602 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3603 boolean checkSecurity,
3604 boolean doRestrict,
3605 Lookup boundCaller) throws IllegalAccessException {
3606 checkMethod(refKind, refc, method);
3607 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3608 if (checkSecurity)
3609 checkSecurityManager(refc, method);
3610 assert(!method.isMethodHandleInvoke());
3611
3612 if (refKind == REF_invokeSpecial &&
3613 refc != lookupClass() &&
3614 !refc.isInterface() &&
3615 refc != lookupClass().getSuperclass() &&
3616 refc.isAssignableFrom(lookupClass())) {
3617 assert(!method.getName().equals("<init>")); // not this code path
3618
3619 // Per JVMS 6.5, desc. of invokespecial instruction:
3620 // If the method is in a superclass of the LC,
3621 // and if our original search was above LC.super,
3622 // repeat the search (symbolic lookup) from LC.super
3623 // and continue with the direct superclass of that class,
3624 // and so forth, until a match is found or no further superclasses exist.
3625 // FIXME: MemberName.resolve should handle this instead.
3626 Class<?> refcAsSuper = lookupClass();
3627 MemberName m2;
3628 do {
3629 refcAsSuper = refcAsSuper.getSuperclass();
3630 m2 = new MemberName(refcAsSuper,
3631 method.getName(),
3632 method.getMethodType(),
3633 REF_invokeSpecial);
3634 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
3635 } while (m2 == null && // no method is found yet
3636 refc != refcAsSuper); // search up to refc
3637 if (m2 == null) throw new InternalError(method.toString());
3638 method = m2;
3639 refc = refcAsSuper;
3640 // redo basic checks
3641 checkMethod(refKind, refc, method);
3642 }
3643 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3644 MethodHandle mh = dmh;
3645 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3646 if ((doRestrict && refKind == REF_invokeSpecial) ||
3647 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
3648 mh = restrictReceiver(method, dmh, lookupClass());
3649 }
3650 mh = maybeBindCaller(method, mh, boundCaller);
3651 mh = mh.setVarargs(method);
3652 return mh;
3653 }
3654 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
3655 throws IllegalAccessException {
3656 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3657 return mh;
3658
3659 // boundCaller must have full privilege access.
3660 // It should have been checked by findBoundCallerLookup. Safe to check this again.
3661 if (!boundCaller.hasFullPrivilegeAccess())
3662 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3663
3664 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
3665 // Note: caller will apply varargs after this step happens.
3666 return cbmh;
3667 }
3668
3669 /** Check access and get the requested field. */
3670 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3671 final boolean checkSecurity = true;
3672 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3673 }
3674 /** Check access and get the requested field, eliding security manager checks. */
3675 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3676 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3677 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3678 }
3679 /** Common code for all fields; do not call directly except from immediately above. */
3680 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
3681 boolean checkSecurity) throws IllegalAccessException {
3682 checkField(refKind, refc, field);
3683 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3684 if (checkSecurity)
3685 checkSecurityManager(refc, field);
3686 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3687 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3688 restrictProtectedReceiver(field));
3689 if (doRestrict)
3690 return restrictReceiver(field, dmh, lookupClass());
3691 return dmh;
3692 }
3693 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3694 Class<?> refc, MemberName getField, MemberName putField)
3695 throws IllegalAccessException {
3696 final boolean checkSecurity = true;
3697 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3698 }
3699 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
3700 Class<?> refc, MemberName getField, MemberName putField)
3701 throws IllegalAccessException {
3702 final boolean checkSecurity = false;
3703 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3704 }
3705 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3706 Class<?> refc, MemberName getField, MemberName putField,
3707 boolean checkSecurity) throws IllegalAccessException {
3708 assert getField.isStatic() == putField.isStatic();
3709 assert getField.isGetter() && putField.isSetter();
3710 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3711 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3712
3713 checkField(getRefKind, refc, getField);
3714 if (checkSecurity)
3715 checkSecurityManager(refc, getField);
3716
3717 if (!putField.isFinal()) {
3718 // A VarHandle does not support updates to final fields, any
3719 // such VarHandle to a final field will be read-only and
3720 // therefore the following write-based accessibility checks are
3721 // only required for non-final fields
3722 checkField(putRefKind, refc, putField);
3723 if (checkSecurity)
3724 checkSecurityManager(refc, putField);
3725 }
3726
3727 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3728 restrictProtectedReceiver(getField));
3729 if (doRestrict) {
3730 assert !getField.isStatic();
3731 // receiver type of VarHandle is too wide; narrow to caller
3732 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3733 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3734 }
3735 refc = lookupClass();
3736 }
3737 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(),
3738 this.allowedModes == TRUSTED && !getField.getDeclaringClass().isHidden());
3739 }
3740 /** Check access and get the requested constructor. */
3741 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3742 final boolean checkSecurity = true;
3743 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3744 }
3745 /** Check access and get the requested constructor, eliding security manager checks. */
3746 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3747 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3748 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3749 }
3750 /** Common code for all constructors; do not call directly except from immediately above. */
3751 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
3752 boolean checkSecurity) throws IllegalAccessException {
3753 assert(ctor.isConstructor());
3754 checkAccess(REF_newInvokeSpecial, refc, ctor);
3755 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3756 if (checkSecurity)
3757 checkSecurityManager(refc, ctor);
3758 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3759 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3760 }
3761
3762 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3763 */
3764 /*non-public*/
3765 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
3766 throws ReflectiveOperationException {
3767 if (!(type instanceof Class || type instanceof MethodType))
3768 throw new InternalError("unresolved MemberName");
3769 MemberName member = new MemberName(refKind, defc, name, type);
3770 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3771 if (mh != null) {
3772 checkSymbolicClass(defc);
3773 return mh;
3774 }
3775 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3776 // Treat MethodHandle.invoke and invokeExact specially.
3777 mh = findVirtualForMH(member.getName(), member.getMethodType());
3778 if (mh != null) {
3779 return mh;
3780 }
3781 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3782 // Treat signature-polymorphic methods on VarHandle specially.
3783 mh = findVirtualForVH(member.getName(), member.getMethodType());
3784 if (mh != null) {
3785 return mh;
3786 }
3787 }
3788 MemberName resolved = resolveOrFail(refKind, member);
3789 mh = getDirectMethodForConstant(refKind, defc, resolved);
3790 if (mh instanceof DirectMethodHandle
3791 && canBeCached(refKind, defc, resolved)) {
3792 MemberName key = mh.internalMemberName();
3793 if (key != null) {
3794 key = key.asNormalOriginal();
3795 }
3796 if (member.equals(key)) { // better safe than sorry
3797 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
3798 }
3799 }
3800 return mh;
3801 }
3802 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
3803 if (refKind == REF_invokeSpecial) {
3804 return false;
3805 }
3806 if (!Modifier.isPublic(defc.getModifiers()) ||
3807 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
3808 !member.isPublic() ||
3809 member.isCallerSensitive()) {
3810 return false;
3811 }
3812 ClassLoader loader = defc.getClassLoader();
3813 if (loader != null) {
3814 ClassLoader sysl = ClassLoader.getSystemClassLoader();
3815 boolean found = false;
3816 while (sysl != null) {
3817 if (loader == sysl) { found = true; break; }
3818 sysl = sysl.getParent();
3819 }
3820 if (!found) {
3821 return false;
3822 }
3823 }
3824 try {
3825 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
3826 new MemberName(refKind, defc, member.getName(), member.getType()));
3827 if (resolved2 == null) {
3828 return false;
3829 }
3830 checkSecurityManager(defc, resolved2);
3831 } catch (SecurityException ex) {
3832 return false;
3833 }
3834 return true;
3835 }
3836 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
3837 throws ReflectiveOperationException {
3838 if (MethodHandleNatives.refKindIsField(refKind)) {
3839 return getDirectFieldNoSecurityManager(refKind, defc, member);
3840 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
3841 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
3842 } else if (refKind == REF_newInvokeSpecial) {
3843 return getDirectConstructorNoSecurityManager(defc, member);
3844 }
3845 // oops
3846 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
3847 }
3848
3849 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
3850 }
3851
3852 /**
3853 * Produces a method handle constructing arrays of a desired type,
3854 * as if by the {@code anewarray} bytecode.
3855 * The return type of the method handle will be the array type.
3856 * The type of its sole argument will be {@code int}, which specifies the size of the array.
3857 *
3858 * <p> If the returned method handle is invoked with a negative
3859 * array size, a {@code NegativeArraySizeException} will be thrown.
3860 *
3861 * @param arrayClass an array type
3862 * @return a method handle which can create arrays of the given type
3863 * @throws NullPointerException if the argument is {@code null}
3864 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
3865 * @see java.lang.reflect.Array#newInstance(Class, int)
3866 * @jvms 6.5 {@code anewarray} Instruction
3867 * @since 9
3868 */
3869 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
3870 if (!arrayClass.isArray()) {
3871 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
3872 }
3873 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
3874 bindTo(arrayClass.getComponentType());
3875 return ani.asType(ani.type().changeReturnType(arrayClass));
3876 }
3877
3878 /**
3879 * Produces a method handle returning the length of an array,
3880 * as if by the {@code arraylength} bytecode.
3881 * The type of the method handle will have {@code int} as return type,
3882 * and its sole argument will be the array type.
3883 *
3884 * <p> If the returned method handle is invoked with a {@code null}
3885 * array reference, a {@code NullPointerException} will be thrown.
3886 *
3887 * @param arrayClass an array type
3888 * @return a method handle which can retrieve the length of an array of the given array type
3889 * @throws NullPointerException if the argument is {@code null}
3890 * @throws IllegalArgumentException if arrayClass is not an array type
3891 * @jvms 6.5 {@code arraylength} Instruction
3892 * @since 9
3893 */
3894 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
3895 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
3896 }
3897
3898 /**
3899 * Produces a method handle giving read access to elements of an array,
3900 * as if by the {@code aaload} bytecode.
3901 * The type of the method handle will have a return type of the array's
3902 * element type. Its first argument will be the array type,
3903 * and the second will be {@code int}.
3904 *
3905 * <p> When the returned method handle is invoked,
3906 * the array reference and array index are checked.
3907 * A {@code NullPointerException} will be thrown if the array reference
3908 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3909 * thrown if the index is negative or if it is greater than or equal to
3910 * the length of the array.
3911 *
3912 * @param arrayClass an array type
3913 * @return a method handle which can load values from the given array type
3914 * @throws NullPointerException if the argument is null
3915 * @throws IllegalArgumentException if arrayClass is not an array type
3916 * @jvms 6.5 {@code aaload} Instruction
3917 */
3918 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
3919 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
3920 }
3921
3922 /**
3923 * Produces a method handle giving write access to elements of an array,
3924 * as if by the {@code astore} bytecode.
3925 * The type of the method handle will have a void return type.
3926 * Its last argument will be the array's element type.
3927 * The first and second arguments will be the array type and int.
3928 *
3929 * <p> When the returned method handle is invoked,
3930 * the array reference and array index are checked.
3931 * A {@code NullPointerException} will be thrown if the array reference
3932 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3933 * thrown if the index is negative or if it is greater than or equal to
3934 * the length of the array.
3935 *
3936 * @param arrayClass the class of an array
3937 * @return a method handle which can store values into the array type
3938 * @throws NullPointerException if the argument is null
3939 * @throws IllegalArgumentException if arrayClass is not an array type
3940 * @jvms 6.5 {@code aastore} Instruction
3941 */
3942 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
3943 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
3944 }
3945
3946 /**
3947 * Produces a VarHandle giving access to elements of an array of type
3948 * {@code arrayClass}. The VarHandle's variable type is the component type
3949 * of {@code arrayClass} and the list of coordinate types is
3950 * {@code (arrayClass, int)}, where the {@code int} coordinate type
3951 * corresponds to an argument that is an index into an array.
3952 * <p>
3953 * Certain access modes of the returned VarHandle are unsupported under
3954 * the following conditions:
3955 * <ul>
3956 * <li>if the component type is anything other than {@code byte},
3957 * {@code short}, {@code char}, {@code int}, {@code long},
3958 * {@code float}, or {@code double} then numeric atomic update access
3959 * modes are unsupported.
3960 * <li>if the field type is anything other than {@code boolean},
3961 * {@code byte}, {@code short}, {@code char}, {@code int} or
3962 * {@code long} then bitwise atomic update access modes are
3963 * unsupported.
3964 * </ul>
3965 * <p>
3966 * If the component type is {@code float} or {@code double} then numeric
3967 * and atomic update access modes compare values using their bitwise
3968 * representation (see {@link Float#floatToRawIntBits} and
3969 * {@link Double#doubleToRawLongBits}, respectively).
3970 *
3971 * <p> When the returned {@code VarHandle} is invoked,
3972 * the array reference and array index are checked.
3973 * A {@code NullPointerException} will be thrown if the array reference
3974 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3975 * thrown if the index is negative or if it is greater than or equal to
3976 * the length of the array.
3977 *
3978 * @apiNote
3979 * Bitwise comparison of {@code float} values or {@code double} values,
3980 * as performed by the numeric and atomic update access modes, differ
3981 * from the primitive {@code ==} operator and the {@link Float#equals}
3982 * and {@link Double#equals} methods, specifically with respect to
3983 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3984 * Care should be taken when performing a compare and set or a compare
3985 * and exchange operation with such values since the operation may
3986 * unexpectedly fail.
3987 * There are many possible NaN values that are considered to be
3988 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3989 * provided by Java can distinguish between them. Operation failure can
3990 * occur if the expected or witness value is a NaN value and it is
3991 * transformed (perhaps in a platform specific manner) into another NaN
3992 * value, and thus has a different bitwise representation (see
3993 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3994 * details).
3995 * The values {@code -0.0} and {@code +0.0} have different bitwise
3996 * representations but are considered equal when using the primitive
3997 * {@code ==} operator. Operation failure can occur if, for example, a
3998 * numeric algorithm computes an expected value to be say {@code -0.0}
3999 * and previously computed the witness value to be say {@code +0.0}.
4000 * @param arrayClass the class of an array, of type {@code T[]}
4001 * @return a VarHandle giving access to elements of an array
4002 * @throws NullPointerException if the arrayClass is null
4003 * @throws IllegalArgumentException if arrayClass is not an array type
4004 * @since 9
4005 */
4006 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4007 return VarHandles.makeArrayElementHandle(arrayClass);
4008 }
4009
4010 /**
4011 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4012 * viewed as if it were a different primitive array type, such as
4013 * {@code int[]} or {@code long[]}.
4014 * The VarHandle's variable type is the component type of
4015 * {@code viewArrayClass} and the list of coordinate types is
4016 * {@code (byte[], int)}, where the {@code int} coordinate type
4017 * corresponds to an argument that is an index into a {@code byte[]} array.
4018 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4019 * array, composing bytes to or from a value of the component type of
4020 * {@code viewArrayClass} according to the given endianness.
4021 * <p>
4022 * The supported component types (variables types) are {@code short},
4023 * {@code char}, {@code int}, {@code long}, {@code float} and
4024 * {@code double}.
4025 * <p>
4026 * Access of bytes at a given index will result in an
4027 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4028 * or greater than the {@code byte[]} array length minus the size (in bytes)
4029 * of {@code T}.
4030 * <p>
4031 * Access of bytes at an index may be aligned or misaligned for {@code T},
4032 * with respect to the underlying memory address, {@code A} say, associated
4033 * with the array and index.
4034 * If access is misaligned then access for anything other than the
4035 * {@code get} and {@code set} access modes will result in an
4036 * {@code IllegalStateException}. In such cases atomic access is only
4037 * guaranteed with respect to the largest power of two that divides the GCD
4038 * of {@code A} and the size (in bytes) of {@code T}.
4039 * If access is aligned then following access modes are supported and are
4040 * guaranteed to support atomic access:
4041 * <ul>
4042 * <li>read write access modes for all {@code T}, with the exception of
4043 * access modes {@code get} and {@code set} for {@code long} and
4044 * {@code double} on 32-bit platforms.
4045 * <li>atomic update access modes for {@code int}, {@code long},
4046 * {@code float} or {@code double}.
4047 * (Future major platform releases of the JDK may support additional
4048 * types for certain currently unsupported access modes.)
4049 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4050 * (Future major platform releases of the JDK may support additional
4051 * numeric types for certain currently unsupported access modes.)
4052 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4053 * (Future major platform releases of the JDK may support additional
4054 * numeric types for certain currently unsupported access modes.)
4055 * </ul>
4056 * <p>
4057 * Misaligned access, and therefore atomicity guarantees, may be determined
4058 * for {@code byte[]} arrays without operating on a specific array. Given
4059 * an {@code index}, {@code T} and it's corresponding boxed type,
4060 * {@code T_BOX}, misalignment may be determined as follows:
4061 * <pre>{@code
4062 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4063 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4064 * alignmentOffset(0, sizeOfT);
4065 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4066 * boolean isMisaligned = misalignedAtIndex != 0;
4067 * }</pre>
4068 * <p>
4069 * If the variable type is {@code float} or {@code double} then atomic
4070 * update access modes compare values using their bitwise representation
4071 * (see {@link Float#floatToRawIntBits} and
4072 * {@link Double#doubleToRawLongBits}, respectively).
4073 * @param viewArrayClass the view array class, with a component type of
4074 * type {@code T}
4075 * @param byteOrder the endianness of the view array elements, as
4076 * stored in the underlying {@code byte} array
4077 * @return a VarHandle giving access to elements of a {@code byte[]} array
4078 * viewed as if elements corresponding to the components type of the view
4079 * array class
4080 * @throws NullPointerException if viewArrayClass or byteOrder is null
4081 * @throws IllegalArgumentException if viewArrayClass is not an array type
4082 * @throws UnsupportedOperationException if the component type of
4083 * viewArrayClass is not supported as a variable type
4084 * @since 9
4085 */
4086 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4087 ByteOrder byteOrder) throws IllegalArgumentException {
4088 Objects.requireNonNull(byteOrder);
4089 return VarHandles.byteArrayViewHandle(viewArrayClass,
4090 byteOrder == ByteOrder.BIG_ENDIAN);
4091 }
4092
4093 /**
4094 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4095 * viewed as if it were an array of elements of a different primitive
4096 * component type to that of {@code byte}, such as {@code int[]} or
4097 * {@code long[]}.
4098 * The VarHandle's variable type is the component type of
4099 * {@code viewArrayClass} and the list of coordinate types is
4100 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4101 * corresponds to an argument that is an index into a {@code byte[]} array.
4102 * The returned VarHandle accesses bytes at an index in a
4103 * {@code ByteBuffer}, composing bytes to or from a value of the component
4104 * type of {@code viewArrayClass} according to the given endianness.
4105 * <p>
4106 * The supported component types (variables types) are {@code short},
4107 * {@code char}, {@code int}, {@code long}, {@code float} and
4108 * {@code double}.
4109 * <p>
4110 * Access will result in a {@code ReadOnlyBufferException} for anything
4111 * other than the read access modes if the {@code ByteBuffer} is read-only.
4112 * <p>
4113 * Access of bytes at a given index will result in an
4114 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4115 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4116 * {@code T}.
4117 * <p>
4118 * Access of bytes at an index may be aligned or misaligned for {@code T},
4119 * with respect to the underlying memory address, {@code A} say, associated
4120 * with the {@code ByteBuffer} and index.
4121 * If access is misaligned then access for anything other than the
4122 * {@code get} and {@code set} access modes will result in an
4123 * {@code IllegalStateException}. In such cases atomic access is only
4124 * guaranteed with respect to the largest power of two that divides the GCD
4125 * of {@code A} and the size (in bytes) of {@code T}.
4126 * If access is aligned then following access modes are supported and are
4127 * guaranteed to support atomic access:
4128 * <ul>
4129 * <li>read write access modes for all {@code T}, with the exception of
4130 * access modes {@code get} and {@code set} for {@code long} and
4131 * {@code double} on 32-bit platforms.
4132 * <li>atomic update access modes for {@code int}, {@code long},
4133 * {@code float} or {@code double}.
4134 * (Future major platform releases of the JDK may support additional
4135 * types for certain currently unsupported access modes.)
4136 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4137 * (Future major platform releases of the JDK may support additional
4138 * numeric types for certain currently unsupported access modes.)
4139 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4140 * (Future major platform releases of the JDK may support additional
4141 * numeric types for certain currently unsupported access modes.)
4142 * </ul>
4143 * <p>
4144 * Misaligned access, and therefore atomicity guarantees, may be determined
4145 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4146 * {@code index}, {@code T} and it's corresponding boxed type,
4147 * {@code T_BOX}, as follows:
4148 * <pre>{@code
4149 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4150 * ByteBuffer bb = ...
4151 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4152 * boolean isMisaligned = misalignedAtIndex != 0;
4153 * }</pre>
4154 * <p>
4155 * If the variable type is {@code float} or {@code double} then atomic
4156 * update access modes compare values using their bitwise representation
4157 * (see {@link Float#floatToRawIntBits} and
4158 * {@link Double#doubleToRawLongBits}, respectively).
4159 * @param viewArrayClass the view array class, with a component type of
4160 * type {@code T}
4161 * @param byteOrder the endianness of the view array elements, as
4162 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4163 * endianness of a {@code ByteBuffer})
4164 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4165 * viewed as if elements corresponding to the components type of the view
4166 * array class
4167 * @throws NullPointerException if viewArrayClass or byteOrder is null
4168 * @throws IllegalArgumentException if viewArrayClass is not an array type
4169 * @throws UnsupportedOperationException if the component type of
4170 * viewArrayClass is not supported as a variable type
4171 * @since 9
4172 */
4173 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4174 ByteOrder byteOrder) throws IllegalArgumentException {
4175 Objects.requireNonNull(byteOrder);
4176 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4177 byteOrder == ByteOrder.BIG_ENDIAN);
4178 }
4179
4180
4181 /// method handle invocation (reflective style)
4182
4183 /**
4184 * Produces a method handle which will invoke any method handle of the
4185 * given {@code type}, with a given number of trailing arguments replaced by
4186 * a single trailing {@code Object[]} array.
4187 * The resulting invoker will be a method handle with the following
4188 * arguments:
4189 * <ul>
4190 * <li>a single {@code MethodHandle} target
4191 * <li>zero or more leading values (counted by {@code leadingArgCount})
4192 * <li>an {@code Object[]} array containing trailing arguments
4193 * </ul>
4194 * <p>
4195 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4196 * the indicated {@code type}.
4197 * That is, if the target is exactly of the given {@code type}, it will behave
4198 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4199 * is used to convert the target to the required {@code type}.
4200 * <p>
4201 * The type of the returned invoker will not be the given {@code type}, but rather
4202 * will have all parameters except the first {@code leadingArgCount}
4203 * replaced by a single array of type {@code Object[]}, which will be
4204 * the final parameter.
4205 * <p>
4206 * Before invoking its target, the invoker will spread the final array, apply
4207 * reference casts as necessary, and unbox and widen primitive arguments.
4208 * If, when the invoker is called, the supplied array argument does
4209 * not have the correct number of elements, the invoker will throw
4210 * an {@link IllegalArgumentException} instead of invoking the target.
4211 * <p>
4212 * This method is equivalent to the following code (though it may be more efficient):
4213 * <blockquote><pre>{@code
4214 MethodHandle invoker = MethodHandles.invoker(type);
4215 int spreadArgCount = type.parameterCount() - leadingArgCount;
4216 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4217 return invoker;
4218 * }</pre></blockquote>
4219 * This method throws no reflective or security exceptions.
4220 * @param type the desired target type
4221 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4222 * @return a method handle suitable for invoking any method handle of the given type
4223 * @throws NullPointerException if {@code type} is null
4224 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4225 * the range from 0 to {@code type.parameterCount()} inclusive,
4226 * or if the resulting method handle's type would have
4227 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4228 */
4229 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4230 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4231 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4232 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4233 return type.invokers().spreadInvoker(leadingArgCount);
4234 }
4235
4236 /**
4237 * Produces a special <em>invoker method handle</em> which can be used to
4238 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4239 * The resulting invoker will have a type which is
4240 * exactly equal to the desired type, except that it will accept
4241 * an additional leading argument of type {@code MethodHandle}.
4242 * <p>
4243 * This method is equivalent to the following code (though it may be more efficient):
4244 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4245 *
4246 * <p style="font-size:smaller;">
4247 * <em>Discussion:</em>
4248 * Invoker method handles can be useful when working with variable method handles
4249 * of unknown types.
4250 * For example, to emulate an {@code invokeExact} call to a variable method
4251 * handle {@code M}, extract its type {@code T},
4252 * look up the invoker method {@code X} for {@code T},
4253 * and call the invoker method, as {@code X.invoke(T, A...)}.
4254 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4255 * is unknown.)
4256 * If spreading, collecting, or other argument transformations are required,
4257 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4258 * method handle values, as long as they are compatible with the type of {@code X}.
4259 * <p style="font-size:smaller;">
4260 * <em>(Note: The invoker method is not available via the Core Reflection API.
4261 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4262 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4263 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4264 * <p>
4265 * This method throws no reflective or security exceptions.
4266 * @param type the desired target type
4267 * @return a method handle suitable for invoking any method handle of the given type
4268 * @throws IllegalArgumentException if the resulting method handle's type would have
4269 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4270 */
4271 public static MethodHandle exactInvoker(MethodType type) {
4272 return type.invokers().exactInvoker();
4273 }
4274
4275 /**
4276 * Produces a special <em>invoker method handle</em> which can be used to
4277 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4278 * The resulting invoker will have a type which is
4279 * exactly equal to the desired type, except that it will accept
4280 * an additional leading argument of type {@code MethodHandle}.
4281 * <p>
4282 * Before invoking its target, if the target differs from the expected type,
4283 * the invoker will apply reference casts as
4284 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4285 * Similarly, the return value will be converted as necessary.
4286 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4287 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4288 * <p>
4289 * This method is equivalent to the following code (though it may be more efficient):
4290 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4291 * <p style="font-size:smaller;">
4292 * <em>Discussion:</em>
4293 * A {@linkplain MethodType#genericMethodType general method type} is one which
4294 * mentions only {@code Object} arguments and return values.
4295 * An invoker for such a type is capable of calling any method handle
4296 * of the same arity as the general type.
4297 * <p style="font-size:smaller;">
4298 * <em>(Note: The invoker method is not available via the Core Reflection API.
4299 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4300 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4301 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4302 * <p>
4303 * This method throws no reflective or security exceptions.
4304 * @param type the desired target type
4305 * @return a method handle suitable for invoking any method handle convertible to the given type
4306 * @throws IllegalArgumentException if the resulting method handle's type would have
4307 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4308 */
4309 public static MethodHandle invoker(MethodType type) {
4310 return type.invokers().genericInvoker();
4311 }
4312
4313 /**
4314 * Produces a special <em>invoker method handle</em> which can be used to
4315 * invoke a signature-polymorphic access mode method on any VarHandle whose
4316 * associated access mode type is compatible with the given type.
4317 * The resulting invoker will have a type which is exactly equal to the
4318 * desired given type, except that it will accept an additional leading
4319 * argument of type {@code VarHandle}.
4320 *
4321 * @param accessMode the VarHandle access mode
4322 * @param type the desired target type
4323 * @return a method handle suitable for invoking an access mode method of
4324 * any VarHandle whose access mode type is of the given type.
4325 * @since 9
4326 */
4327 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4328 return type.invokers().varHandleMethodExactInvoker(accessMode);
4329 }
4330
4331 /**
4332 * Produces a special <em>invoker method handle</em> which can be used to
4333 * invoke a signature-polymorphic access mode method on any VarHandle whose
4334 * associated access mode type is compatible with the given type.
4335 * The resulting invoker will have a type which is exactly equal to the
4336 * desired given type, except that it will accept an additional leading
4337 * argument of type {@code VarHandle}.
4338 * <p>
4339 * Before invoking its target, if the access mode type differs from the
4340 * desired given type, the invoker will apply reference casts as necessary
4341 * and box, unbox, or widen primitive values, as if by
4342 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4343 * converted as necessary.
4344 * <p>
4345 * This method is equivalent to the following code (though it may be more
4346 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4347 *
4348 * @param accessMode the VarHandle access mode
4349 * @param type the desired target type
4350 * @return a method handle suitable for invoking an access mode method of
4351 * any VarHandle whose access mode type is convertible to the given
4352 * type.
4353 * @since 9
4354 */
4355 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4356 return type.invokers().varHandleMethodInvoker(accessMode);
4357 }
4358
4359 /*non-public*/
4360 static MethodHandle basicInvoker(MethodType type) {
4361 return type.invokers().basicInvoker();
4362 }
4363
4364 /// method handle modification (creation from other method handles)
4365
4366 /**
4367 * Produces a method handle which adapts the type of the
4368 * given method handle to a new type by pairwise argument and return type conversion.
4369 * The original type and new type must have the same number of arguments.
4370 * The resulting method handle is guaranteed to report a type
4371 * which is equal to the desired new type.
4372 * <p>
4373 * If the original type and new type are equal, returns target.
4374 * <p>
4375 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4376 * and some additional conversions are also applied if those conversions fail.
4377 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4378 * if possible, before or instead of any conversions done by {@code asType}:
4379 * <ul>
4380 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4381 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4382 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4383 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4384 * the boolean is converted to a byte value, 1 for true, 0 for false.
4385 * (This treatment follows the usage of the bytecode verifier.)
4386 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4387 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
4388 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4389 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4390 * then a Java casting conversion (JLS 5.5) is applied.
4391 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4392 * widening and/or narrowing.)
4393 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4394 * conversion will be applied at runtime, possibly followed
4395 * by a Java casting conversion (JLS 5.5) on the primitive value,
4396 * possibly followed by a conversion from byte to boolean by testing
4397 * the low-order bit.
4398 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4399 * and if the reference is null at runtime, a zero value is introduced.
4400 * </ul>
4401 * @param target the method handle to invoke after arguments are retyped
4402 * @param newType the expected type of the new method handle
4403 * @return a method handle which delegates to the target after performing
4404 * any necessary argument conversions, and arranges for any
4405 * necessary return value conversions
4406 * @throws NullPointerException if either argument is null
4407 * @throws WrongMethodTypeException if the conversion cannot be made
4408 * @see MethodHandle#asType
4409 */
4410 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4411 explicitCastArgumentsChecks(target, newType);
4412 // use the asTypeCache when possible:
4413 MethodType oldType = target.type();
4414 if (oldType == newType) return target;
4415 if (oldType.explicitCastEquivalentToAsType(newType)) {
4416 return target.asFixedArity().asType(newType);
4417 }
4418 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4419 }
4420
4421 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4422 if (target.type().parameterCount() != newType.parameterCount()) {
4423 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4424 }
4425 }
4426
4427 /**
4428 * Produces a method handle which adapts the calling sequence of the
4429 * given method handle to a new type, by reordering the arguments.
4430 * The resulting method handle is guaranteed to report a type
4431 * which is equal to the desired new type.
4432 * <p>
4433 * The given array controls the reordering.
4434 * Call {@code #I} the number of incoming parameters (the value
4435 * {@code newType.parameterCount()}, and call {@code #O} the number
4436 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4437 * Then the length of the reordering array must be {@code #O},
4438 * and each element must be a non-negative number less than {@code #I}.
4439 * For every {@code N} less than {@code #O}, the {@code N}-th
4440 * outgoing argument will be taken from the {@code I}-th incoming
4441 * argument, where {@code I} is {@code reorder[N]}.
4442 * <p>
4443 * No argument or return value conversions are applied.
4444 * The type of each incoming argument, as determined by {@code newType},
4445 * must be identical to the type of the corresponding outgoing parameter
4446 * or parameters in the target method handle.
4447 * The return type of {@code newType} must be identical to the return
4448 * type of the original target.
4449 * <p>
4450 * The reordering array need not specify an actual permutation.
4451 * An incoming argument will be duplicated if its index appears
4452 * more than once in the array, and an incoming argument will be dropped
4453 * if its index does not appear in the array.
4454 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4455 * incoming arguments which are not mentioned in the reordering array
4456 * may be of any type, as determined only by {@code newType}.
4457 * <blockquote><pre>{@code
4458 import static java.lang.invoke.MethodHandles.*;
4459 import static java.lang.invoke.MethodType.*;
4460 ...
4461 MethodType intfn1 = methodType(int.class, int.class);
4462 MethodType intfn2 = methodType(int.class, int.class, int.class);
4463 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4464 assert(sub.type().equals(intfn2));
4465 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4466 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4467 assert((int)rsub.invokeExact(1, 100) == 99);
4468 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4469 assert(add.type().equals(intfn2));
4470 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4471 assert(twice.type().equals(intfn1));
4472 assert((int)twice.invokeExact(21) == 42);
4473 * }</pre></blockquote>
4474 * <p>
4475 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4476 * variable-arity method handle}, even if the original target method handle was.
4477 * @param target the method handle to invoke after arguments are reordered
4478 * @param newType the expected type of the new method handle
4479 * @param reorder an index array which controls the reordering
4480 * @return a method handle which delegates to the target after it
4481 * drops unused arguments and moves and/or duplicates the other arguments
4482 * @throws NullPointerException if any argument is null
4483 * @throws IllegalArgumentException if the index array length is not equal to
4484 * the arity of the target, or if any index array element
4485 * not a valid index for a parameter of {@code newType},
4486 * or if two corresponding parameter types in
4487 * {@code target.type()} and {@code newType} are not identical,
4488 */
4489 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4490 reorder = reorder.clone(); // get a private copy
4491 MethodType oldType = target.type();
4492 permuteArgumentChecks(reorder, newType, oldType);
4493 // first detect dropped arguments and handle them separately
4494 int[] originalReorder = reorder;
4495 BoundMethodHandle result = target.rebind();
4496 LambdaForm form = result.form;
4497 int newArity = newType.parameterCount();
4498 // Normalize the reordering into a real permutation,
4499 // by removing duplicates and adding dropped elements.
4500 // This somewhat improves lambda form caching, as well
4501 // as simplifying the transform by breaking it up into steps.
4502 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4503 if (ddIdx > 0) {
4504 // We found a duplicated entry at reorder[ddIdx].
4505 // Example: (x,y,z)->asList(x,y,z)
4506 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4507 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4508 // The starred element corresponds to the argument
4509 // deleted by the dupArgumentForm transform.
4510 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4511 boolean killFirst = false;
4512 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4513 // Set killFirst if the dup is larger than an intervening position.
4514 // This will remove at least one inversion from the permutation.
4515 if (dupVal > val) killFirst = true;
4516 }
4517 if (!killFirst) {
4518 srcPos = dstPos;
4519 dstPos = ddIdx;
4520 }
4521 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4522 assert (reorder[srcPos] == reorder[dstPos]);
4523 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4524 // contract the reordering by removing the element at dstPos
4525 int tailPos = dstPos + 1;
4526 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4527 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4528 } else {
4529 int dropVal = ~ddIdx, insPos = 0;
4530 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4531 // Find first element of reorder larger than dropVal.
4532 // This is where we will insert the dropVal.
4533 insPos += 1;
4534 }
4535 Class<?> ptype = newType.parameterType(dropVal);
4536 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4537 oldType = oldType.insertParameterTypes(insPos, ptype);
4538 // expand the reordering by inserting an element at insPos
4539 int tailPos = insPos + 1;
4540 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4541 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4542 reorder[insPos] = dropVal;
4543 }
4544 assert (permuteArgumentChecks(reorder, newType, oldType));
4545 }
4546 assert (reorder.length == newArity); // a perfect permutation
4547 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4548 form = form.editor().permuteArgumentsForm(1, reorder);
4549 if (newType == result.type() && form == result.internalForm())
4550 return result;
4551 return result.copyWith(newType, form);
4552 }
4553
4554 /**
4555 * Return an indication of any duplicate or omission in reorder.
4556 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4557 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4558 * Otherwise, return zero.
4559 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4560 */
4561 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4562 final int BIT_LIMIT = 63; // max number of bits in bit mask
4563 if (newArity < BIT_LIMIT) {
4564 long mask = 0;
4565 for (int i = 0; i < reorder.length; i++) {
4566 int arg = reorder[i];
4567 if (arg >= newArity) {
4568 return reorder.length;
4569 }
4570 long bit = 1L << arg;
4571 if ((mask & bit) != 0) {
4572 return i; // >0 indicates a dup
4573 }
4574 mask |= bit;
4575 }
4576 if (mask == (1L << newArity) - 1) {
4577 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4578 return 0;
4579 }
4580 // find first zero
4581 long zeroBit = Long.lowestOneBit(~mask);
4582 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4583 assert(zeroPos <= newArity);
4584 if (zeroPos == newArity) {
4585 return 0;
4586 }
4587 return ~zeroPos;
4588 } else {
4589 // same algorithm, different bit set
4590 BitSet mask = new BitSet(newArity);
4591 for (int i = 0; i < reorder.length; i++) {
4592 int arg = reorder[i];
4593 if (arg >= newArity) {
4594 return reorder.length;
4595 }
4596 if (mask.get(arg)) {
4597 return i; // >0 indicates a dup
4598 }
4599 mask.set(arg);
4600 }
4601 int zeroPos = mask.nextClearBit(0);
4602 assert(zeroPos <= newArity);
4603 if (zeroPos == newArity) {
4604 return 0;
4605 }
4606 return ~zeroPos;
4607 }
4608 }
4609
4610 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4611 if (newType.returnType() != oldType.returnType())
4612 throw newIllegalArgumentException("return types do not match",
4613 oldType, newType);
4614 if (reorder.length == oldType.parameterCount()) {
4615 int limit = newType.parameterCount();
4616 boolean bad = false;
4617 for (int j = 0; j < reorder.length; j++) {
4618 int i = reorder[j];
4619 if (i < 0 || i >= limit) {
4620 bad = true; break;
4621 }
4622 Class<?> src = newType.parameterType(i);
4623 Class<?> dst = oldType.parameterType(j);
4624 if (src != dst)
4625 throw newIllegalArgumentException("parameter types do not match after reorder",
4626 oldType, newType);
4627 }
4628 if (!bad) return true;
4629 }
4630 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
4631 }
4632
4633 /**
4634 * Produces a method handle of the requested return type which returns the given
4635 * constant value every time it is invoked.
4636 * <p>
4637 * Before the method handle is returned, the passed-in value is converted to the requested type.
4638 * If the requested type is primitive, widening primitive conversions are attempted,
4639 * else reference conversions are attempted.
4640 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4641 * @param type the return type of the desired method handle
4642 * @param value the value to return
4643 * @return a method handle of the given return type and no arguments, which always returns the given value
4644 * @throws NullPointerException if the {@code type} argument is null
4645 * @throws ClassCastException if the value cannot be converted to the required return type
4646 * @throws IllegalArgumentException if the given type is {@code void.class}
4647 */
4648 public static MethodHandle constant(Class<?> type, Object value) {
4649 if (type.isPrimitive()) {
4650 if (type == void.class)
4651 throw newIllegalArgumentException("void type");
4652 Wrapper w = Wrapper.forPrimitiveType(type);
4653 value = w.convert(value, type);
4654 if (w.zero().equals(value))
4655 return zero(w, type);
4656 return insertArguments(identity(type), 0, value);
4657 } else {
4658 if (value == null)
4659 return zero(Wrapper.OBJECT, type);
4660 return identity(type).bindTo(value);
4661 }
4662 }
4663
4664 /**
4665 * Produces a method handle which returns its sole argument when invoked.
4666 * @param type the type of the sole parameter and return value of the desired method handle
4667 * @return a unary method handle which accepts and returns the given type
4668 * @throws NullPointerException if the argument is null
4669 * @throws IllegalArgumentException if the given type is {@code void.class}
4670 */
4671 public static MethodHandle identity(Class<?> type) {
4672 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4673 int pos = btw.ordinal();
4674 MethodHandle ident = IDENTITY_MHS[pos];
4675 if (ident == null) {
4676 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4677 }
4678 if (ident.type().returnType() == type)
4679 return ident;
4680 // something like identity(Foo.class); do not bother to intern these
4681 assert (btw == Wrapper.OBJECT);
4682 return makeIdentity(type);
4683 }
4684
4685 /**
4686 * Produces a constant method handle of the requested return type which
4687 * returns the default value for that type every time it is invoked.
4688 * The resulting constant method handle will have no side effects.
4689 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4690 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4691 * since {@code explicitCastArguments} converts {@code null} to default values.
4692 * @param type the expected return type of the desired method handle
4693 * @return a constant method handle that takes no arguments
4694 * and returns the default value of the given type (or void, if the type is void)
4695 * @throws NullPointerException if the argument is null
4696 * @see MethodHandles#constant
4697 * @see MethodHandles#empty
4698 * @see MethodHandles#explicitCastArguments
4699 * @since 9
4700 */
4701 public static MethodHandle zero(Class<?> type) {
4702 Objects.requireNonNull(type);
4703 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
4704 }
4705
4706 private static MethodHandle identityOrVoid(Class<?> type) {
4707 return type == void.class ? zero(type) : identity(type);
4708 }
4709
4710 /**
4711 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4712 * and returns a suitable default depending on the return type.
4713 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4714 * <p>The returned method handle is equivalent to
4715 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4716 *
4717 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4718 * {@code guardWithTest(pred, target, empty(target.type())}.
4719 * @param type the type of the desired method handle
4720 * @return a constant method handle of the given type, which returns a default value of the given return type
4721 * @throws NullPointerException if the argument is null
4722 * @see MethodHandles#zero
4723 * @see MethodHandles#constant
4724 * @since 9
4725 */
4726 public static MethodHandle empty(MethodType type) {
4727 Objects.requireNonNull(type);
4728 return dropArguments(zero(type.returnType()), 0, type.parameterList());
4729 }
4730
4731 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4732 private static MethodHandle makeIdentity(Class<?> ptype) {
4733 MethodType mtype = methodType(ptype, ptype);
4734 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4735 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4736 }
4737
4738 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
4739 int pos = btw.ordinal();
4740 MethodHandle zero = ZERO_MHS[pos];
4741 if (zero == null) {
4742 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
4743 }
4744 if (zero.type().returnType() == rtype)
4745 return zero;
4746 assert(btw == Wrapper.OBJECT);
4747 return makeZero(rtype);
4748 }
4749 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4750 private static MethodHandle makeZero(Class<?> rtype) {
4751 MethodType mtype = methodType(rtype);
4752 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
4753 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
4754 }
4755
4756 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4757 // Simulate a CAS, to avoid racy duplication of results.
4758 MethodHandle prev = cache[pos];
4759 if (prev != null) return prev;
4760 return cache[pos] = value;
4761 }
4762
4763 /**
4764 * Provides a target method handle with one or more <em>bound arguments</em>
4765 * in advance of the method handle's invocation.
4766 * The formal parameters to the target corresponding to the bound
4767 * arguments are called <em>bound parameters</em>.
4768 * Returns a new method handle which saves away the bound arguments.
4769 * When it is invoked, it receives arguments for any non-bound parameters,
4770 * binds the saved arguments to their corresponding parameters,
4771 * and calls the original target.
4772 * <p>
4773 * The type of the new method handle will drop the types for the bound
4774 * parameters from the original target type, since the new method handle
4775 * will no longer require those arguments to be supplied by its callers.
4776 * <p>
4777 * Each given argument object must match the corresponding bound parameter type.
4778 * If a bound parameter type is a primitive, the argument object
4779 * must be a wrapper, and will be unboxed to produce the primitive value.
4780 * <p>
4781 * The {@code pos} argument selects which parameters are to be bound.
4782 * It may range between zero and <i>N-L</i> (inclusively),
4783 * where <i>N</i> is the arity of the target method handle
4784 * and <i>L</i> is the length of the values array.
4785 * <p>
4786 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4787 * variable-arity method handle}, even if the original target method handle was.
4788 * @param target the method handle to invoke after the argument is inserted
4789 * @param pos where to insert the argument (zero for the first)
4790 * @param values the series of arguments to insert
4791 * @return a method handle which inserts an additional argument,
4792 * before calling the original method handle
4793 * @throws NullPointerException if the target or the {@code values} array is null
4794 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
4795 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4796 * is the length of the values array.
4797 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4798 * type.
4799 * @see MethodHandle#bindTo
4800 */
4801 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4802 int insCount = values.length;
4803 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4804 if (insCount == 0) return target;
4805 BoundMethodHandle result = target.rebind();
4806 for (int i = 0; i < insCount; i++) {
4807 Object value = values[i];
4808 Class<?> ptype = ptypes[pos+i];
4809 if (ptype.isPrimitive()) {
4810 result = insertArgumentPrimitive(result, pos, ptype, value);
4811 } else {
4812 value = ptype.cast(value); // throw CCE if needed
4813 result = result.bindArgumentL(pos, value);
4814 }
4815 }
4816 return result;
4817 }
4818
4819 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4820 Class<?> ptype, Object value) {
4821 Wrapper w = Wrapper.forPrimitiveType(ptype);
4822 // perform unboxing and/or primitive conversion
4823 value = w.convert(value, ptype);
4824 switch (w) {
4825 case INT: return result.bindArgumentI(pos, (int)value);
4826 case LONG: return result.bindArgumentJ(pos, (long)value);
4827 case FLOAT: return result.bindArgumentF(pos, (float)value);
4828 case DOUBLE: return result.bindArgumentD(pos, (double)value);
4829 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
4830 }
4831 }
4832
4833 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
4834 MethodType oldType = target.type();
4835 int outargs = oldType.parameterCount();
4836 int inargs = outargs - insCount;
4837 if (inargs < 0)
4838 throw newIllegalArgumentException("too many values to insert");
4839 if (pos < 0 || pos > inargs)
4840 throw newIllegalArgumentException("no argument type to append");
4841 return oldType.ptypes();
4842 }
4843
4844 /**
4845 * Produces a method handle which will discard some dummy arguments
4846 * before calling some other specified <i>target</i> method handle.
4847 * The type of the new method handle will be the same as the target's type,
4848 * except it will also include the dummy argument types,
4849 * at some given position.
4850 * <p>
4851 * The {@code pos} argument may range between zero and <i>N</i>,
4852 * where <i>N</i> is the arity of the target.
4853 * If {@code pos} is zero, the dummy arguments will precede
4854 * the target's real arguments; if {@code pos} is <i>N</i>
4855 * they will come after.
4856 * <p>
4857 * <b>Example:</b>
4858 * <blockquote><pre>{@code
4859 import static java.lang.invoke.MethodHandles.*;
4860 import static java.lang.invoke.MethodType.*;
4861 ...
4862 MethodHandle cat = lookup().findVirtual(String.class,
4863 "concat", methodType(String.class, String.class));
4864 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4865 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
4866 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
4867 assertEquals(bigType, d0.type());
4868 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
4869 * }</pre></blockquote>
4870 * <p>
4871 * This method is also equivalent to the following code:
4872 * <blockquote><pre>
4873 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
4874 * </pre></blockquote>
4875 * @param target the method handle to invoke after the arguments are dropped
4876 * @param pos position of first argument to drop (zero for the leftmost)
4877 * @param valueTypes the type(s) of the argument(s) to drop
4878 * @return a method handle which drops arguments of the given types,
4879 * before calling the original method handle
4880 * @throws NullPointerException if the target is null,
4881 * or if the {@code valueTypes} list or any of its elements is null
4882 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4883 * or if {@code pos} is negative or greater than the arity of the target,
4884 * or if the new method handle's type would have too many parameters
4885 */
4886 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4887 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
4888 }
4889
4890 private static List<Class<?>> copyTypes(Object[] array) {
4891 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
4892 }
4893
4894 private static MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4895 MethodType oldType = target.type(); // get NPE
4896 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
4897 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
4898 if (dropped == 0) return target;
4899 BoundMethodHandle result = target.rebind();
4900 LambdaForm lform = result.form;
4901 int insertFormArg = 1 + pos;
4902 for (Class<?> ptype : valueTypes) {
4903 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
4904 }
4905 result = result.copyWith(newType, lform);
4906 return result;
4907 }
4908
4909 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
4910 int dropped = valueTypes.size();
4911 MethodType.checkSlotCount(dropped);
4912 int outargs = oldType.parameterCount();
4913 int inargs = outargs + dropped;
4914 if (pos < 0 || pos > outargs)
4915 throw newIllegalArgumentException("no argument type to remove"
4916 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
4917 );
4918 return dropped;
4919 }
4920
4921 /**
4922 * Produces a method handle which will discard some dummy arguments
4923 * before calling some other specified <i>target</i> method handle.
4924 * The type of the new method handle will be the same as the target's type,
4925 * except it will also include the dummy argument types,
4926 * at some given position.
4927 * <p>
4928 * The {@code pos} argument may range between zero and <i>N</i>,
4929 * where <i>N</i> is the arity of the target.
4930 * If {@code pos} is zero, the dummy arguments will precede
4931 * the target's real arguments; if {@code pos} is <i>N</i>
4932 * they will come after.
4933 * @apiNote
4934 * <blockquote><pre>{@code
4935 import static java.lang.invoke.MethodHandles.*;
4936 import static java.lang.invoke.MethodType.*;
4937 ...
4938 MethodHandle cat = lookup().findVirtual(String.class,
4939 "concat", methodType(String.class, String.class));
4940 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4941 MethodHandle d0 = dropArguments(cat, 0, String.class);
4942 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
4943 MethodHandle d1 = dropArguments(cat, 1, String.class);
4944 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4945 MethodHandle d2 = dropArguments(cat, 2, String.class);
4946 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4947 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4948 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4949 * }</pre></blockquote>
4950 * <p>
4951 * This method is also equivalent to the following code:
4952 * <blockquote><pre>
4953 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4954 * </pre></blockquote>
4955 * @param target the method handle to invoke after the arguments are dropped
4956 * @param pos position of first argument to drop (zero for the leftmost)
4957 * @param valueTypes the type(s) of the argument(s) to drop
4958 * @return a method handle which drops arguments of the given types,
4959 * before calling the original method handle
4960 * @throws NullPointerException if the target is null,
4961 * or if the {@code valueTypes} array or any of its elements is null
4962 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4963 * or if {@code pos} is negative or greater than the arity of the target,
4964 * or if the new method handle's type would have
4965 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4966 */
4967 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4968 return dropArguments0(target, pos, copyTypes(valueTypes));
4969 }
4970
4971 // private version which allows caller some freedom with error handling
4972 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4973 boolean nullOnFailure) {
4974 newTypes = copyTypes(newTypes.toArray());
4975 List<Class<?>> oldTypes = target.type().parameterList();
4976 int match = oldTypes.size();
4977 if (skip != 0) {
4978 if (skip < 0 || skip > match) {
4979 throw newIllegalArgumentException("illegal skip", skip, target);
4980 }
4981 oldTypes = oldTypes.subList(skip, match);
4982 match -= skip;
4983 }
4984 List<Class<?>> addTypes = newTypes;
4985 int add = addTypes.size();
4986 if (pos != 0) {
4987 if (pos < 0 || pos > add) {
4988 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4989 }
4990 addTypes = addTypes.subList(pos, add);
4991 add -= pos;
4992 assert(addTypes.size() == add);
4993 }
4994 // Do not add types which already match the existing arguments.
4995 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4996 if (nullOnFailure) {
4997 return null;
4998 }
4999 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
5000 }
5001 addTypes = addTypes.subList(match, add);
5002 add -= match;
5003 assert(addTypes.size() == add);
5004 // newTypes: ( P*[pos], M*[match], A*[add] )
5005 // target: ( S*[skip], M*[match] )
5006 MethodHandle adapter = target;
5007 if (add > 0) {
5008 adapter = dropArguments0(adapter, skip+ match, addTypes);
5009 }
5010 // adapter: (S*[skip], M*[match], A*[add] )
5011 if (pos > 0) {
5012 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
5013 }
5014 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5015 return adapter;
5016 }
5017
5018 /**
5019 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5020 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5021 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5022 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5023 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5024 * {@link #dropArguments(MethodHandle, int, Class[])}.
5025 * <p>
5026 * The resulting handle will have the same return type as the target handle.
5027 * <p>
5028 * In more formal terms, assume these two type lists:<ul>
5029 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5030 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5031 * {@code newTypes}.
5032 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5033 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5034 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5035 * sub-list.
5036 * </ul>
5037 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5038 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5039 * {@link #dropArguments(MethodHandle, int, Class[])}.
5040 *
5041 * @apiNote
5042 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5043 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5044 * <blockquote><pre>{@code
5045 import static java.lang.invoke.MethodHandles.*;
5046 import static java.lang.invoke.MethodType.*;
5047 ...
5048 ...
5049 MethodHandle h0 = constant(boolean.class, true);
5050 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5051 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5052 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5053 if (h1.type().parameterCount() < h2.type().parameterCount())
5054 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5055 else
5056 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5057 MethodHandle h3 = guardWithTest(h0, h1, h2);
5058 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5059 * }</pre></blockquote>
5060 * @param target the method handle to adapt
5061 * @param skip number of targets parameters to disregard (they will be unchanged)
5062 * @param newTypes the list of types to match {@code target}'s parameter type list to
5063 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5064 * @return a possibly adapted method handle
5065 * @throws NullPointerException if either argument is null
5066 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5067 * or if {@code skip} is negative or greater than the arity of the target,
5068 * or if {@code pos} is negative or greater than the newTypes list size,
5069 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5070 * {@code pos}.
5071 * @since 9
5072 */
5073 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5074 Objects.requireNonNull(target);
5075 Objects.requireNonNull(newTypes);
5076 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
5077 }
5078
5079 /**
5080 * Adapts a target method handle by pre-processing
5081 * one or more of its arguments, each with its own unary filter function,
5082 * and then calling the target with each pre-processed argument
5083 * replaced by the result of its corresponding filter function.
5084 * <p>
5085 * The pre-processing is performed by one or more method handles,
5086 * specified in the elements of the {@code filters} array.
5087 * The first element of the filter array corresponds to the {@code pos}
5088 * argument of the target, and so on in sequence.
5089 * The filter functions are invoked in left to right order.
5090 * <p>
5091 * Null arguments in the array are treated as identity functions,
5092 * and the corresponding arguments left unchanged.
5093 * (If there are no non-null elements in the array, the original target is returned.)
5094 * Each filter is applied to the corresponding argument of the adapter.
5095 * <p>
5096 * If a filter {@code F} applies to the {@code N}th argument of
5097 * the target, then {@code F} must be a method handle which
5098 * takes exactly one argument. The type of {@code F}'s sole argument
5099 * replaces the corresponding argument type of the target
5100 * in the resulting adapted method handle.
5101 * The return type of {@code F} must be identical to the corresponding
5102 * parameter type of the target.
5103 * <p>
5104 * It is an error if there are elements of {@code filters}
5105 * (null or not)
5106 * which do not correspond to argument positions in the target.
5107 * <p><b>Example:</b>
5108 * <blockquote><pre>{@code
5109 import static java.lang.invoke.MethodHandles.*;
5110 import static java.lang.invoke.MethodType.*;
5111 ...
5112 MethodHandle cat = lookup().findVirtual(String.class,
5113 "concat", methodType(String.class, String.class));
5114 MethodHandle upcase = lookup().findVirtual(String.class,
5115 "toUpperCase", methodType(String.class));
5116 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5117 MethodHandle f0 = filterArguments(cat, 0, upcase);
5118 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5119 MethodHandle f1 = filterArguments(cat, 1, upcase);
5120 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5121 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5122 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5123 * }</pre></blockquote>
5124 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5125 * denotes the return type of both the {@code target} and resulting adapter.
5126 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5127 * of the parameters and arguments that precede and follow the filter position
5128 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5129 * values of the filtered parameters and arguments; they also represent the
5130 * return types of the {@code filter[i]} handles. The latter accept arguments
5131 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5132 * the resulting adapter.
5133 * <blockquote><pre>{@code
5134 * T target(P... p, A[i]... a[i], B... b);
5135 * A[i] filter[i](V[i]);
5136 * T adapter(P... p, V[i]... v[i], B... b) {
5137 * return target(p..., filter[i](v[i])..., b...);
5138 * }
5139 * }</pre></blockquote>
5140 * <p>
5141 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5142 * variable-arity method handle}, even if the original target method handle was.
5143 *
5144 * @param target the method handle to invoke after arguments are filtered
5145 * @param pos the position of the first argument to filter
5146 * @param filters method handles to call initially on filtered arguments
5147 * @return method handle which incorporates the specified argument filtering logic
5148 * @throws NullPointerException if the target is null
5149 * or if the {@code filters} array is null
5150 * @throws IllegalArgumentException if a non-null element of {@code filters}
5151 * does not match a corresponding argument type of target as described above,
5152 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5153 * or if the resulting method handle's type would have
5154 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5155 */
5156 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5157 // In method types arguments start at index 0, while the LF
5158 // editor have the MH receiver at position 0 - adjust appropriately.
5159 final int MH_RECEIVER_OFFSET = 1;
5160 filterArgumentsCheckArity(target, pos, filters);
5161 MethodHandle adapter = target;
5162
5163 // keep track of currently matched filters, as to optimize repeated filters
5164 int index = 0;
5165 int[] positions = new int[filters.length];
5166 MethodHandle filter = null;
5167
5168 // process filters in reverse order so that the invocation of
5169 // the resulting adapter will invoke the filters in left-to-right order
5170 for (int i = filters.length - 1; i >= 0; --i) {
5171 MethodHandle newFilter = filters[i];
5172 if (newFilter == null) continue; // ignore null elements of filters
5173
5174 // flush changes on update
5175 if (filter != newFilter) {
5176 if (filter != null) {
5177 if (index > 1) {
5178 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5179 } else {
5180 adapter = filterArgument(adapter, positions[0] - 1, filter);
5181 }
5182 }
5183 filter = newFilter;
5184 index = 0;
5185 }
5186
5187 filterArgumentChecks(target, pos + i, newFilter);
5188 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5189 }
5190 if (index > 1) {
5191 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5192 } else if (index == 1) {
5193 adapter = filterArgument(adapter, positions[0] - 1, filter);
5194 }
5195 return adapter;
5196 }
5197
5198 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5199 MethodType targetType = adapter.type();
5200 MethodType filterType = filter.type();
5201 BoundMethodHandle result = adapter.rebind();
5202 Class<?> newParamType = filterType.parameterType(0);
5203
5204 Class<?>[] ptypes = targetType.ptypes().clone();
5205 for (int pos : positions) {
5206 ptypes[pos - 1] = newParamType;
5207 }
5208 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
5209
5210 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5211 return result.copyWithExtendL(newType, lform, filter);
5212 }
5213
5214 /*non-public*/
5215 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5216 filterArgumentChecks(target, pos, filter);
5217 MethodType targetType = target.type();
5218 MethodType filterType = filter.type();
5219 BoundMethodHandle result = target.rebind();
5220 Class<?> newParamType = filterType.parameterType(0);
5221 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5222 MethodType newType = targetType.changeParameterType(pos, newParamType);
5223 result = result.copyWithExtendL(newType, lform, filter);
5224 return result;
5225 }
5226
5227 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5228 MethodType targetType = target.type();
5229 int maxPos = targetType.parameterCount();
5230 if (pos + filters.length > maxPos)
5231 throw newIllegalArgumentException("too many filters");
5232 }
5233
5234 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5235 MethodType targetType = target.type();
5236 MethodType filterType = filter.type();
5237 if (filterType.parameterCount() != 1
5238 || filterType.returnType() != targetType.parameterType(pos))
5239 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5240 }
5241
5242 /**
5243 * Adapts a target method handle by pre-processing
5244 * a sub-sequence of its arguments with a filter (another method handle).
5245 * The pre-processed arguments are replaced by the result (if any) of the
5246 * filter function.
5247 * The target is then called on the modified (usually shortened) argument list.
5248 * <p>
5249 * If the filter returns a value, the target must accept that value as
5250 * its argument in position {@code pos}, preceded and/or followed by
5251 * any arguments not passed to the filter.
5252 * If the filter returns void, the target must accept all arguments
5253 * not passed to the filter.
5254 * No arguments are reordered, and a result returned from the filter
5255 * replaces (in order) the whole subsequence of arguments originally
5256 * passed to the adapter.
5257 * <p>
5258 * The argument types (if any) of the filter
5259 * replace zero or one argument types of the target, at position {@code pos},
5260 * in the resulting adapted method handle.
5261 * The return type of the filter (if any) must be identical to the
5262 * argument type of the target at position {@code pos}, and that target argument
5263 * is supplied by the return value of the filter.
5264 * <p>
5265 * In all cases, {@code pos} must be greater than or equal to zero, and
5266 * {@code pos} must also be less than or equal to the target's arity.
5267 * <p><b>Example:</b>
5268 * <blockquote><pre>{@code
5269 import static java.lang.invoke.MethodHandles.*;
5270 import static java.lang.invoke.MethodType.*;
5271 ...
5272 MethodHandle deepToString = publicLookup()
5273 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5274
5275 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5276 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5277
5278 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5279 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5280
5281 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5282 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5283 assertEquals("[top, [up, down], strange]",
5284 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5285
5286 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5287 assertEquals("[top, [up, down], [strange]]",
5288 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5289
5290 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5291 assertEquals("[top, [[up, down, strange], charm], bottom]",
5292 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5293 * }</pre></blockquote>
5294 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5295 * represents the return type of the {@code target} and resulting adapter.
5296 * {@code V}/{@code v} stand for the return type and value of the
5297 * {@code filter}, which are also found in the signature and arguments of
5298 * the {@code target}, respectively, unless {@code V} is {@code void}.
5299 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5300 * and values preceding and following the collection position, {@code pos},
5301 * in the {@code target}'s signature. They also turn up in the resulting
5302 * adapter's signature and arguments, where they surround
5303 * {@code B}/{@code b}, which represent the parameter types and arguments
5304 * to the {@code filter} (if any).
5305 * <blockquote><pre>{@code
5306 * T target(A...,V,C...);
5307 * V filter(B...);
5308 * T adapter(A... a,B... b,C... c) {
5309 * V v = filter(b...);
5310 * return target(a...,v,c...);
5311 * }
5312 * // and if the filter has no arguments:
5313 * T target2(A...,V,C...);
5314 * V filter2();
5315 * T adapter2(A... a,C... c) {
5316 * V v = filter2();
5317 * return target2(a...,v,c...);
5318 * }
5319 * // and if the filter has a void return:
5320 * T target3(A...,C...);
5321 * void filter3(B...);
5322 * T adapter3(A... a,B... b,C... c) {
5323 * filter3(b...);
5324 * return target3(a...,c...);
5325 * }
5326 * }</pre></blockquote>
5327 * <p>
5328 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5329 * one which first "folds" the affected arguments, and then drops them, in separate
5330 * steps as follows:
5331 * <blockquote><pre>{@code
5332 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5333 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5334 * }</pre></blockquote>
5335 * If the target method handle consumes no arguments besides than the result
5336 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5337 * is equivalent to {@code filterReturnValue(coll, mh)}.
5338 * If the filter method handle {@code coll} consumes one argument and produces
5339 * a non-void result, then {@code collectArguments(mh, N, coll)}
5340 * is equivalent to {@code filterArguments(mh, N, coll)}.
5341 * Other equivalences are possible but would require argument permutation.
5342 * <p>
5343 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5344 * variable-arity method handle}, even if the original target method handle was.
5345 *
5346 * @param target the method handle to invoke after filtering the subsequence of arguments
5347 * @param pos the position of the first adapter argument to pass to the filter,
5348 * and/or the target argument which receives the result of the filter
5349 * @param filter method handle to call on the subsequence of arguments
5350 * @return method handle which incorporates the specified argument subsequence filtering logic
5351 * @throws NullPointerException if either argument is null
5352 * @throws IllegalArgumentException if the return type of {@code filter}
5353 * is non-void and is not the same as the {@code pos} argument of the target,
5354 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5355 * or if the resulting method handle's type would have
5356 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5357 * @see MethodHandles#foldArguments
5358 * @see MethodHandles#filterArguments
5359 * @see MethodHandles#filterReturnValue
5360 */
5361 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5362 MethodType newType = collectArgumentsChecks(target, pos, filter);
5363 MethodType collectorType = filter.type();
5364 BoundMethodHandle result = target.rebind();
5365 LambdaForm lform;
5366 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
5367 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
5368 if (lform != null) {
5369 return result.copyWith(newType, lform);
5370 }
5371 }
5372 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5373 return result.copyWithExtendL(newType, lform, filter);
5374 }
5375
5376 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5377 MethodType targetType = target.type();
5378 MethodType filterType = filter.type();
5379 Class<?> rtype = filterType.returnType();
5380 List<Class<?>> filterArgs = filterType.parameterList();
5381 if (rtype == void.class) {
5382 return targetType.insertParameterTypes(pos, filterArgs);
5383 }
5384 if (rtype != targetType.parameterType(pos)) {
5385 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5386 }
5387 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
5388 }
5389
5390 /**
5391 * Adapts a target method handle by post-processing
5392 * its return value (if any) with a filter (another method handle).
5393 * The result of the filter is returned from the adapter.
5394 * <p>
5395 * If the target returns a value, the filter must accept that value as
5396 * its only argument.
5397 * If the target returns void, the filter must accept no arguments.
5398 * <p>
5399 * The return type of the filter
5400 * replaces the return type of the target
5401 * in the resulting adapted method handle.
5402 * The argument type of the filter (if any) must be identical to the
5403 * return type of the target.
5404 * <p><b>Example:</b>
5405 * <blockquote><pre>{@code
5406 import static java.lang.invoke.MethodHandles.*;
5407 import static java.lang.invoke.MethodType.*;
5408 ...
5409 MethodHandle cat = lookup().findVirtual(String.class,
5410 "concat", methodType(String.class, String.class));
5411 MethodHandle length = lookup().findVirtual(String.class,
5412 "length", methodType(int.class));
5413 System.out.println((String) cat.invokeExact("x", "y")); // xy
5414 MethodHandle f0 = filterReturnValue(cat, length);
5415 System.out.println((int) f0.invokeExact("x", "y")); // 2
5416 * }</pre></blockquote>
5417 * <p>Here is pseudocode for the resulting adapter. In the code,
5418 * {@code T}/{@code t} represent the result type and value of the
5419 * {@code target}; {@code V}, the result type of the {@code filter}; and
5420 * {@code A}/{@code a}, the types and values of the parameters and arguments
5421 * of the {@code target} as well as the resulting adapter.
5422 * <blockquote><pre>{@code
5423 * T target(A...);
5424 * V filter(T);
5425 * V adapter(A... a) {
5426 * T t = target(a...);
5427 * return filter(t);
5428 * }
5429 * // and if the target has a void return:
5430 * void target2(A...);
5431 * V filter2();
5432 * V adapter2(A... a) {
5433 * target2(a...);
5434 * return filter2();
5435 * }
5436 * // and if the filter has a void return:
5437 * T target3(A...);
5438 * void filter3(V);
5439 * void adapter3(A... a) {
5440 * T t = target3(a...);
5441 * filter3(t);
5442 * }
5443 * }</pre></blockquote>
5444 * <p>
5445 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5446 * variable-arity method handle}, even if the original target method handle was.
5447 * @param target the method handle to invoke before filtering the return value
5448 * @param filter method handle to call on the return value
5449 * @return method handle which incorporates the specified return value filtering logic
5450 * @throws NullPointerException if either argument is null
5451 * @throws IllegalArgumentException if the argument list of {@code filter}
5452 * does not match the return type of target as described above
5453 */
5454 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5455 MethodType targetType = target.type();
5456 MethodType filterType = filter.type();
5457 filterReturnValueChecks(targetType, filterType);
5458 BoundMethodHandle result = target.rebind();
5459 BasicType rtype = BasicType.basicType(filterType.returnType());
5460 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5461 MethodType newType = targetType.changeReturnType(filterType.returnType());
5462 result = result.copyWithExtendL(newType, lform, filter);
5463 return result;
5464 }
5465
5466 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5467 Class<?> rtype = targetType.returnType();
5468 int filterValues = filterType.parameterCount();
5469 if (filterValues == 0
5470 ? (rtype != void.class)
5471 : (rtype != filterType.parameterType(0) || filterValues != 1))
5472 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5473 }
5474
5475 /**
5476 * Adapts a target method handle by pre-processing
5477 * some of its arguments, and then calling the target with
5478 * the result of the pre-processing, inserted into the original
5479 * sequence of arguments.
5480 * <p>
5481 * The pre-processing is performed by {@code combiner}, a second method handle.
5482 * Of the arguments passed to the adapter, the first {@code N} arguments
5483 * are copied to the combiner, which is then called.
5484 * (Here, {@code N} is defined as the parameter count of the combiner.)
5485 * After this, control passes to the target, with any result
5486 * from the combiner inserted before the original {@code N} incoming
5487 * arguments.
5488 * <p>
5489 * If the combiner returns a value, the first parameter type of the target
5490 * must be identical with the return type of the combiner, and the next
5491 * {@code N} parameter types of the target must exactly match the parameters
5492 * of the combiner.
5493 * <p>
5494 * If the combiner has a void return, no result will be inserted,
5495 * and the first {@code N} parameter types of the target
5496 * must exactly match the parameters of the combiner.
5497 * <p>
5498 * The resulting adapter is the same type as the target, except that the
5499 * first parameter type is dropped,
5500 * if it corresponds to the result of the combiner.
5501 * <p>
5502 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5503 * that either the combiner or the target does not wish to receive.
5504 * If some of the incoming arguments are destined only for the combiner,
5505 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5506 * arguments will not need to be live on the stack on entry to the
5507 * target.)
5508 * <p><b>Example:</b>
5509 * <blockquote><pre>{@code
5510 import static java.lang.invoke.MethodHandles.*;
5511 import static java.lang.invoke.MethodType.*;
5512 ...
5513 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5514 "println", methodType(void.class, String.class))
5515 .bindTo(System.out);
5516 MethodHandle cat = lookup().findVirtual(String.class,
5517 "concat", methodType(String.class, String.class));
5518 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5519 MethodHandle catTrace = foldArguments(cat, trace);
5520 // also prints "boo":
5521 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5522 * }</pre></blockquote>
5523 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5524 * represents the result type of the {@code target} and resulting adapter.
5525 * {@code V}/{@code v} represent the type and value of the parameter and argument
5526 * of {@code target} that precedes the folding position; {@code V} also is
5527 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5528 * types and values of the {@code N} parameters and arguments at the folding
5529 * position. {@code B}/{@code b} represent the types and values of the
5530 * {@code target} parameters and arguments that follow the folded parameters
5531 * and arguments.
5532 * <blockquote><pre>{@code
5533 * // there are N arguments in A...
5534 * T target(V, A[N]..., B...);
5535 * V combiner(A...);
5536 * T adapter(A... a, B... b) {
5537 * V v = combiner(a...);
5538 * return target(v, a..., b...);
5539 * }
5540 * // and if the combiner has a void return:
5541 * T target2(A[N]..., B...);
5542 * void combiner2(A...);
5543 * T adapter2(A... a, B... b) {
5544 * combiner2(a...);
5545 * return target2(a..., b...);
5546 * }
5547 * }</pre></blockquote>
5548 * <p>
5549 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5550 * variable-arity method handle}, even if the original target method handle was.
5551 * @param target the method handle to invoke after arguments are combined
5552 * @param combiner method handle to call initially on the incoming arguments
5553 * @return method handle which incorporates the specified argument folding logic
5554 * @throws NullPointerException if either argument is null
5555 * @throws IllegalArgumentException if {@code combiner}'s return type
5556 * is non-void and not the same as the first argument type of
5557 * the target, or if the initial {@code N} argument types
5558 * of the target
5559 * (skipping one matching the {@code combiner}'s return type)
5560 * are not identical with the argument types of {@code combiner}
5561 */
5562 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5563 return foldArguments(target, 0, combiner);
5564 }
5565
5566 /**
5567 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5568 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5569 * before the folded arguments.
5570 * <p>
5571 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5572 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5573 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5574 * 0.
5575 *
5576 * @apiNote Example:
5577 * <blockquote><pre>{@code
5578 import static java.lang.invoke.MethodHandles.*;
5579 import static java.lang.invoke.MethodType.*;
5580 ...
5581 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5582 "println", methodType(void.class, String.class))
5583 .bindTo(System.out);
5584 MethodHandle cat = lookup().findVirtual(String.class,
5585 "concat", methodType(String.class, String.class));
5586 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5587 MethodHandle catTrace = foldArguments(cat, 1, trace);
5588 // also prints "jum":
5589 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5590 * }</pre></blockquote>
5591 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5592 * represents the result type of the {@code target} and resulting adapter.
5593 * {@code V}/{@code v} represent the type and value of the parameter and argument
5594 * of {@code target} that precedes the folding position; {@code V} also is
5595 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5596 * types and values of the {@code N} parameters and arguments at the folding
5597 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5598 * and values of the {@code target} parameters and arguments that precede and
5599 * follow the folded parameters and arguments starting at {@code pos},
5600 * respectively.
5601 * <blockquote><pre>{@code
5602 * // there are N arguments in A...
5603 * T target(Z..., V, A[N]..., B...);
5604 * V combiner(A...);
5605 * T adapter(Z... z, A... a, B... b) {
5606 * V v = combiner(a...);
5607 * return target(z..., v, a..., b...);
5608 * }
5609 * // and if the combiner has a void return:
5610 * T target2(Z..., A[N]..., B...);
5611 * void combiner2(A...);
5612 * T adapter2(Z... z, A... a, B... b) {
5613 * combiner2(a...);
5614 * return target2(z..., a..., b...);
5615 * }
5616 * }</pre></blockquote>
5617 * <p>
5618 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5619 * variable-arity method handle}, even if the original target method handle was.
5620 *
5621 * @param target the method handle to invoke after arguments are combined
5622 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5623 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5624 * @param combiner method handle to call initially on the incoming arguments
5625 * @return method handle which incorporates the specified argument folding logic
5626 * @throws NullPointerException if either argument is null
5627 * @throws IllegalArgumentException if either of the following two conditions holds:
5628 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5629 * {@code pos} of the target signature;
5630 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5631 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5632 *
5633 * @see #foldArguments(MethodHandle, MethodHandle)
5634 * @since 9
5635 */
5636 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5637 MethodType targetType = target.type();
5638 MethodType combinerType = combiner.type();
5639 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5640 BoundMethodHandle result = target.rebind();
5641 boolean dropResult = rtype == void.class;
5642 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5643 MethodType newType = targetType;
5644 if (!dropResult) {
5645 newType = newType.dropParameterTypes(pos, pos + 1);
5646 }
5647 result = result.copyWithExtendL(newType, lform, combiner);
5648 return result;
5649 }
5650
5651 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5652 int foldArgs = combinerType.parameterCount();
5653 Class<?> rtype = combinerType.returnType();
5654 int foldVals = rtype == void.class ? 0 : 1;
5655 int afterInsertPos = foldPos + foldVals;
5656 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5657 if (ok) {
5658 for (int i = 0; i < foldArgs; i++) {
5659 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5660 ok = false;
5661 break;
5662 }
5663 }
5664 }
5665 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5666 ok = false;
5667 if (!ok)
5668 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5669 return rtype;
5670 }
5671
5672 /**
5673 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5674 * of the pre-processing replacing the argument at the given position.
5675 *
5676 * @param target the method handle to invoke after arguments are combined
5677 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5678 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5679 * @param combiner method handle to call initially on the incoming arguments
5680 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5681 * @return method handle which incorporates the specified argument folding logic
5682 * @throws NullPointerException if either argument is null
5683 * @throws IllegalArgumentException if either of the following two conditions holds:
5684 * (1) {@code combiner}'s return type is not the same as the argument type at position
5685 * {@code pos} of the target signature;
5686 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5687 * not identical with the argument types of {@code combiner}.
5688 */
5689 /*non-public*/
5690 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5691 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5692 }
5693
5694 /**
5695 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5696 * the pre-processing inserted into the original sequence of arguments at the given position.
5697 *
5698 * @param target the method handle to invoke after arguments are combined
5699 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5700 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5701 * @param combiner method handle to call initially on the incoming arguments
5702 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5703 * @return method handle which incorporates the specified argument folding logic
5704 * @throws NullPointerException if either argument is null
5705 * @throws IllegalArgumentException if either of the following two conditions holds:
5706 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5707 * {@code pos} of the target signature;
5708 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5709 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5710 * with the argument types of {@code combiner}.
5711 */
5712 /*non-public*/
5713 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5714 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5715 }
5716
5717 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5718 MethodType targetType = target.type();
5719 MethodType combinerType = combiner.type();
5720 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5721 BoundMethodHandle result = target.rebind();
5722
5723 MethodType newType = targetType;
5724 LambdaForm lform;
5725 if (filter) {
5726 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5727 } else {
5728 boolean dropResult = rtype == void.class;
5729 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5730 if (!dropResult) {
5731 newType = newType.dropParameterTypes(position, position + 1);
5732 }
5733 }
5734 result = result.copyWithExtendL(newType, lform, combiner);
5735 return result;
5736 }
5737
5738 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5739 int combinerArgs = combinerType.parameterCount();
5740 if (argPos.length != combinerArgs) {
5741 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5742 }
5743 Class<?> rtype = combinerType.returnType();
5744
5745 for (int i = 0; i < combinerArgs; i++) {
5746 int arg = argPos[i];
5747 if (arg < 0 || arg > targetType.parameterCount()) {
5748 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5749 }
5750 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5751 throw newIllegalArgumentException("target argument type at position " + arg
5752 + " must match combiner argument type at index " + i + ": " + targetType
5753 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5754 }
5755 }
5756 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5757 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5758 }
5759 return rtype;
5760 }
5761
5762 /**
5763 * Makes a method handle which adapts a target method handle,
5764 * by guarding it with a test, a boolean-valued method handle.
5765 * If the guard fails, a fallback handle is called instead.
5766 * All three method handles must have the same corresponding
5767 * argument and return types, except that the return type
5768 * of the test must be boolean, and the test is allowed
5769 * to have fewer arguments than the other two method handles.
5770 * <p>
5771 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5772 * represents the uniform result type of the three involved handles;
5773 * {@code A}/{@code a}, the types and values of the {@code target}
5774 * parameters and arguments that are consumed by the {@code test}; and
5775 * {@code B}/{@code b}, those types and values of the {@code target}
5776 * parameters and arguments that are not consumed by the {@code test}.
5777 * <blockquote><pre>{@code
5778 * boolean test(A...);
5779 * T target(A...,B...);
5780 * T fallback(A...,B...);
5781 * T adapter(A... a,B... b) {
5782 * if (test(a...))
5783 * return target(a..., b...);
5784 * else
5785 * return fallback(a..., b...);
5786 * }
5787 * }</pre></blockquote>
5788 * Note that the test arguments ({@code a...} in the pseudocode) cannot
5789 * be modified by execution of the test, and so are passed unchanged
5790 * from the caller to the target or fallback as appropriate.
5791 * @param test method handle used for test, must return boolean
5792 * @param target method handle to call if test passes
5793 * @param fallback method handle to call if test fails
5794 * @return method handle which incorporates the specified if/then/else logic
5795 * @throws NullPointerException if any argument is null
5796 * @throws IllegalArgumentException if {@code test} does not return boolean,
5797 * or if all three method types do not match (with the return
5798 * type of {@code test} changed to match that of the target).
5799 */
5800 public static MethodHandle guardWithTest(MethodHandle test,
5801 MethodHandle target,
5802 MethodHandle fallback) {
5803 MethodType gtype = test.type();
5804 MethodType ttype = target.type();
5805 MethodType ftype = fallback.type();
5806 if (!ttype.equals(ftype))
5807 throw misMatchedTypes("target and fallback types", ttype, ftype);
5808 if (gtype.returnType() != boolean.class)
5809 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
5810 List<Class<?>> targs = ttype.parameterList();
5811 test = dropArgumentsToMatch(test, 0, targs, 0, true);
5812 if (test == null) {
5813 throw misMatchedTypes("target and test types", ttype, gtype);
5814 }
5815 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
5816 }
5817
5818 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
5819 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
5820 }
5821
5822 /**
5823 * Makes a method handle which adapts a target method handle,
5824 * by running it inside an exception handler.
5825 * If the target returns normally, the adapter returns that value.
5826 * If an exception matching the specified type is thrown, the fallback
5827 * handle is called instead on the exception, plus the original arguments.
5828 * <p>
5829 * The target and handler must have the same corresponding
5830 * argument and return types, except that handler may omit trailing arguments
5831 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
5832 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
5833 * <p>
5834 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5835 * represents the return type of the {@code target} and {@code handler},
5836 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
5837 * the types and values of arguments to the resulting handle consumed by
5838 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
5839 * resulting handle discarded by {@code handler}.
5840 * <blockquote><pre>{@code
5841 * T target(A..., B...);
5842 * T handler(ExType, A...);
5843 * T adapter(A... a, B... b) {
5844 * try {
5845 * return target(a..., b...);
5846 * } catch (ExType ex) {
5847 * return handler(ex, a...);
5848 * }
5849 * }
5850 * }</pre></blockquote>
5851 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5852 * be modified by execution of the target, and so are passed unchanged
5853 * from the caller to the handler, if the handler is invoked.
5854 * <p>
5855 * The target and handler must return the same type, even if the handler
5856 * always throws. (This might happen, for instance, because the handler
5857 * is simulating a {@code finally} clause).
5858 * To create such a throwing handler, compose the handler creation logic
5859 * with {@link #throwException throwException},
5860 * in order to create a method handle of the correct return type.
5861 * @param target method handle to call
5862 * @param exType the type of exception which the handler will catch
5863 * @param handler method handle to call if a matching exception is thrown
5864 * @return method handle which incorporates the specified try/catch logic
5865 * @throws NullPointerException if any argument is null
5866 * @throws IllegalArgumentException if {@code handler} does not accept
5867 * the given exception type, or if the method handle types do
5868 * not match in their return types and their
5869 * corresponding parameters
5870 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
5871 */
5872 public static MethodHandle catchException(MethodHandle target,
5873 Class<? extends Throwable> exType,
5874 MethodHandle handler) {
5875 MethodType ttype = target.type();
5876 MethodType htype = handler.type();
5877 if (!Throwable.class.isAssignableFrom(exType))
5878 throw new ClassCastException(exType.getName());
5879 if (htype.parameterCount() < 1 ||
5880 !htype.parameterType(0).isAssignableFrom(exType))
5881 throw newIllegalArgumentException("handler does not accept exception type "+exType);
5882 if (htype.returnType() != ttype.returnType())
5883 throw misMatchedTypes("target and handler return types", ttype, htype);
5884 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
5885 if (handler == null) {
5886 throw misMatchedTypes("target and handler types", ttype, htype);
5887 }
5888 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
5889 }
5890
5891 /**
5892 * Produces a method handle which will throw exceptions of the given {@code exType}.
5893 * The method handle will accept a single argument of {@code exType},
5894 * and immediately throw it as an exception.
5895 * The method type will nominally specify a return of {@code returnType}.
5896 * The return type may be anything convenient: It doesn't matter to the
5897 * method handle's behavior, since it will never return normally.
5898 * @param returnType the return type of the desired method handle
5899 * @param exType the parameter type of the desired method handle
5900 * @return method handle which can throw the given exceptions
5901 * @throws NullPointerException if either argument is null
5902 */
5903 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
5904 if (!Throwable.class.isAssignableFrom(exType))
5905 throw new ClassCastException(exType.getName());
5906 return MethodHandleImpl.throwException(methodType(returnType, exType));
5907 }
5908
5909 /**
5910 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
5911 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
5912 * delivers the loop's result, which is the return value of the resulting handle.
5913 * <p>
5914 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
5915 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
5916 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
5917 * terms of method handles, each clause will specify up to four independent actions:<ul>
5918 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
5919 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
5920 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
5921 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
5922 * </ul>
5923 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
5924 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
5925 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
5926 * <p>
5927 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
5928 * this case. See below for a detailed description.
5929 * <p>
5930 * <em>Parameters optional everywhere:</em>
5931 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
5932 * As an exception, the init functions cannot take any {@code v} parameters,
5933 * because those values are not yet computed when the init functions are executed.
5934 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
5935 * In fact, any clause function may take no arguments at all.
5936 * <p>
5937 * <em>Loop parameters:</em>
5938 * A clause function may take all the iteration variable values it is entitled to, in which case
5939 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
5940 * with their types and values notated as {@code (A...)} and {@code (a...)}.
5941 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
5942 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
5943 * init function is automatically a loop parameter {@code a}.)
5944 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
5945 * These loop parameters act as loop-invariant values visible across the whole loop.
5946 * <p>
5947 * <em>Parameters visible everywhere:</em>
5948 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
5949 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
5950 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
5951 * Most clause functions will not need all of this information, but they will be formally connected to it
5952 * as if by {@link #dropArguments}.
5953 * <a id="astar"></a>
5954 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
5955 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
5956 * In that notation, the general form of an init function parameter list
5957 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
5958 * <p>
5959 * <em>Checking clause structure:</em>
5960 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
5961 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
5962 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
5963 * met by the inputs to the loop combinator.
5964 * <p>
5965 * <em>Effectively identical sequences:</em>
5966 * <a id="effid"></a>
5967 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
5968 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
5969 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
5970 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
5971 * that longest list.
5972 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
5973 * and the same is true if more sequences of the form {@code (V... A*)} are added.
5974 * <p>
5975 * <em>Step 0: Determine clause structure.</em><ol type="a">
5976 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
5977 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
5978 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
5979 * four. Padding takes place by appending elements to the array.
5980 * <li>Clauses with all {@code null}s are disregarded.
5981 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
5982 * </ol>
5983 * <p>
5984 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
5985 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
5986 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
5987 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
5988 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
5989 * iteration variable type.
5990 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
5991 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
5992 * </ol>
5993 * <p>
5994 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
5995 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
5996 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
5997 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
5998 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
5999 * (These types will be checked in step 2, along with all the clause function types.)
6000 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6001 * <li>All of the collected parameter lists must be effectively identical.
6002 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6003 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6004 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6005 * the "internal parameter list".
6006 * </ul>
6007 * <p>
6008 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6009 * <li>Examine fini function return types, disregarding omitted fini functions.
6010 * <li>If there are no fini functions, the loop return type is {@code void}.
6011 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6012 * type.
6013 * </ol>
6014 * <p>
6015 * <em>Step 1D: Check other types.</em><ol type="a">
6016 * <li>There must be at least one non-omitted pred function.
6017 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6018 * </ol>
6019 * <p>
6020 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6021 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6022 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6023 * (Note that their parameter lists are already effectively identical to this list.)
6024 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6025 * effectively identical to the internal parameter list {@code (V... A...)}.
6026 * </ol>
6027 * <p>
6028 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6029 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6030 * type.
6031 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6032 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6033 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6034 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6035 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6036 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6037 * loop return type.
6038 * </ol>
6039 * <p>
6040 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6041 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6042 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6043 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6044 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6045 * pad out the end of the list.
6046 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6047 * </ol>
6048 * <p>
6049 * <em>Final observations.</em><ol type="a">
6050 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6051 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6052 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6053 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6054 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6055 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6056 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6057 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6058 * </ol>
6059 * <p>
6060 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6061 * <ul>
6062 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6063 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6064 * (Only one {@code Pn} has to be non-{@code null}.)
6065 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6066 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6067 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6068 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6069 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6070 * the resulting loop handle's parameter types {@code (A...)}.
6071 * </ul>
6072 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6073 * which is natural if most of the loop computation happens in the steps. For some loops,
6074 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6075 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6076 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6077 * where the init functions will need the extra parameters. For such reasons, the rules for
6078 * determining these parameters are as symmetric as possible, across all clause parts.
6079 * In general, the loop parameters function as common invariant values across the whole
6080 * loop, while the iteration variables function as common variant values, or (if there is
6081 * no step function) as internal loop invariant temporaries.
6082 * <p>
6083 * <em>Loop execution.</em><ol type="a">
6084 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6085 * every clause function. These locals are loop invariant.
6086 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6087 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6088 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6089 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6090 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6091 * (in argument order).
6092 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6093 * returns {@code false}.
6094 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6095 * sequence {@code (v...)} of loop variables.
6096 * The updated value is immediately visible to all subsequent function calls.
6097 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6098 * (of type {@code R}) is returned from the loop as a whole.
6099 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6100 * except by throwing an exception.
6101 * </ol>
6102 * <p>
6103 * <em>Usage tips.</em>
6104 * <ul>
6105 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6106 * sometimes a step function only needs to observe the current value of its own variable.
6107 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6108 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6109 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6110 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6111 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6112 * <li>If some of the clause functions are virtual methods on an instance, the instance
6113 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6114 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6115 * will be the first iteration variable value, and it will be easy to use virtual
6116 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6117 * </ul>
6118 * <p>
6119 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6120 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6121 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6122 * <blockquote><pre>{@code
6123 * V... init...(A...);
6124 * boolean pred...(V..., A...);
6125 * V... step...(V..., A...);
6126 * R fini...(V..., A...);
6127 * R loop(A... a) {
6128 * V... v... = init...(a...);
6129 * for (;;) {
6130 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6131 * v = s(v..., a...);
6132 * if (!p(v..., a...)) {
6133 * return f(v..., a...);
6134 * }
6135 * }
6136 * }
6137 * }
6138 * }</pre></blockquote>
6139 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6140 * to their full length, even though individual clause functions may neglect to take them all.
6141 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6142 *
6143 * @apiNote Example:
6144 * <blockquote><pre>{@code
6145 * // iterative implementation of the factorial function as a loop handle
6146 * static int one(int k) { return 1; }
6147 * static int inc(int i, int acc, int k) { return i + 1; }
6148 * static int mult(int i, int acc, int k) { return i * acc; }
6149 * static boolean pred(int i, int acc, int k) { return i < k; }
6150 * static int fin(int i, int acc, int k) { return acc; }
6151 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6152 * // null initializer for counter, should initialize to 0
6153 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6154 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6155 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6156 * assertEquals(120, loop.invoke(5));
6157 * }</pre></blockquote>
6158 * The same example, dropping arguments and using combinators:
6159 * <blockquote><pre>{@code
6160 * // simplified implementation of the factorial function as a loop handle
6161 * static int inc(int i) { return i + 1; } // drop acc, k
6162 * static int mult(int i, int acc) { return i * acc; } //drop k
6163 * static boolean cmp(int i, int k) { return i < k; }
6164 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6165 * // null initializer for counter, should initialize to 0
6166 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6167 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6168 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6169 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6170 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6171 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6172 * assertEquals(720, loop.invoke(6));
6173 * }</pre></blockquote>
6174 * A similar example, using a helper object to hold a loop parameter:
6175 * <blockquote><pre>{@code
6176 * // instance-based implementation of the factorial function as a loop handle
6177 * static class FacLoop {
6178 * final int k;
6179 * FacLoop(int k) { this.k = k; }
6180 * int inc(int i) { return i + 1; }
6181 * int mult(int i, int acc) { return i * acc; }
6182 * boolean pred(int i) { return i < k; }
6183 * int fin(int i, int acc) { return acc; }
6184 * }
6185 * // assume MH_FacLoop is a handle to the constructor
6186 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6187 * // null initializer for counter, should initialize to 0
6188 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6189 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6190 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6191 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6192 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6193 * assertEquals(5040, loop.invoke(7));
6194 * }</pre></blockquote>
6195 *
6196 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6197 *
6198 * @return a method handle embodying the looping behavior as defined by the arguments.
6199 *
6200 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6201 *
6202 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6203 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6204 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6205 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6206 * @since 9
6207 */
6208 public static MethodHandle loop(MethodHandle[]... clauses) {
6209 // Step 0: determine clause structure.
6210 loopChecks0(clauses);
6211
6212 List<MethodHandle> init = new ArrayList<>();
6213 List<MethodHandle> step = new ArrayList<>();
6214 List<MethodHandle> pred = new ArrayList<>();
6215 List<MethodHandle> fini = new ArrayList<>();
6216
6217 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6218 init.add(clause[0]); // all clauses have at least length 1
6219 step.add(clause.length <= 1 ? null : clause[1]);
6220 pred.add(clause.length <= 2 ? null : clause[2]);
6221 fini.add(clause.length <= 3 ? null : clause[3]);
6222 });
6223
6224 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6225 final int nclauses = init.size();
6226
6227 // Step 1A: determine iteration variables (V...).
6228 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6229 for (int i = 0; i < nclauses; ++i) {
6230 MethodHandle in = init.get(i);
6231 MethodHandle st = step.get(i);
6232 if (in == null && st == null) {
6233 iterationVariableTypes.add(void.class);
6234 } else if (in != null && st != null) {
6235 loopChecks1a(i, in, st);
6236 iterationVariableTypes.add(in.type().returnType());
6237 } else {
6238 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6239 }
6240 }
6241 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
6242 collect(Collectors.toList());
6243
6244 // Step 1B: determine loop parameters (A...).
6245 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6246 loopChecks1b(init, commonSuffix);
6247
6248 // Step 1C: determine loop return type.
6249 // Step 1D: check other types.
6250 // local variable required here; see JDK-8223553
6251 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6252 .map(MethodType::returnType);
6253 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6254 loopChecks1cd(pred, fini, loopReturnType);
6255
6256 // Step 2: determine parameter lists.
6257 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6258 commonParameterSequence.addAll(commonSuffix);
6259 loopChecks2(step, pred, fini, commonParameterSequence);
6260
6261 // Step 3: fill in omitted functions.
6262 for (int i = 0; i < nclauses; ++i) {
6263 Class<?> t = iterationVariableTypes.get(i);
6264 if (init.get(i) == null) {
6265 init.set(i, empty(methodType(t, commonSuffix)));
6266 }
6267 if (step.get(i) == null) {
6268 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6269 }
6270 if (pred.get(i) == null) {
6271 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
6272 }
6273 if (fini.get(i) == null) {
6274 fini.set(i, empty(methodType(t, commonParameterSequence)));
6275 }
6276 }
6277
6278 // Step 4: fill in missing parameter types.
6279 // Also convert all handles to fixed-arity handles.
6280 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6281 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6282 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6283 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6284
6285 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6286 allMatch(pl -> pl.equals(commonSuffix));
6287 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6288 allMatch(pl -> pl.equals(commonParameterSequence));
6289
6290 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6291 }
6292
6293 private static void loopChecks0(MethodHandle[][] clauses) {
6294 if (clauses == null || clauses.length == 0) {
6295 throw newIllegalArgumentException("null or no clauses passed");
6296 }
6297 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6298 throw newIllegalArgumentException("null clauses are not allowed");
6299 }
6300 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6301 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6302 }
6303 }
6304
6305 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6306 if (in.type().returnType() != st.type().returnType()) {
6307 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6308 st.type().returnType());
6309 }
6310 }
6311
6312 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6313 final List<Class<?>> empty = List.of();
6314 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
6315 // take only those that can contribute to a common suffix because they are longer than the prefix
6316 map(MethodHandle::type).
6317 filter(t -> t.parameterCount() > skipSize).
6318 map(MethodType::parameterList).
6319 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6320 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
6321 }
6322
6323 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
6324 final List<Class<?>> empty = List.of();
6325 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6326 }
6327
6328 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6329 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6330 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6331 return longestParameterList(Arrays.asList(longest1, longest2));
6332 }
6333
6334 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6335 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6336 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6337 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6338 " (common suffix: " + commonSuffix + ")");
6339 }
6340 }
6341
6342 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6343 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6344 anyMatch(t -> t != loopReturnType)) {
6345 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6346 loopReturnType + ")");
6347 }
6348
6349 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
6350 throw newIllegalArgumentException("no predicate found", pred);
6351 }
6352 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6353 anyMatch(t -> t != boolean.class)) {
6354 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6355 }
6356 }
6357
6358 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6359 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6360 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6361 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6362 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6363 }
6364 }
6365
6366 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6367 return hs.stream().map(h -> {
6368 int pc = h.type().parameterCount();
6369 int tpsize = targetParams.size();
6370 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
6371 }).collect(Collectors.toList());
6372 }
6373
6374 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6375 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
6376 }
6377
6378 /**
6379 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6380 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6381 * <p>
6382 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6383 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6384 * evaluates to {@code true}).
6385 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6386 * <p>
6387 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6388 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6389 * and updated with the value returned from its invocation. The result of loop execution will be
6390 * the final value of the additional loop-local variable (if present).
6391 * <p>
6392 * The following rules hold for these argument handles:<ul>
6393 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6394 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6395 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6396 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6397 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6398 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6399 * It will constrain the parameter lists of the other loop parts.
6400 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6401 * list {@code (A...)} is called the <em>external parameter list</em>.
6402 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6403 * additional state variable of the loop.
6404 * The body must both accept and return a value of this type {@code V}.
6405 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6406 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6407 * <a href="MethodHandles.html#effid">effectively identical</a>
6408 * to the external parameter list {@code (A...)}.
6409 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6410 * {@linkplain #empty default value}.
6411 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6412 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6413 * effectively identical to the internal parameter list.
6414 * </ul>
6415 * <p>
6416 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6417 * <li>The loop handle's result type is the result type {@code V} of the body.
6418 * <li>The loop handle's parameter types are the types {@code (A...)},
6419 * from the external parameter list.
6420 * </ul>
6421 * <p>
6422 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6423 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6424 * passed to the loop.
6425 * <blockquote><pre>{@code
6426 * V init(A...);
6427 * boolean pred(V, A...);
6428 * V body(V, A...);
6429 * V whileLoop(A... a...) {
6430 * V v = init(a...);
6431 * while (pred(v, a...)) {
6432 * v = body(v, a...);
6433 * }
6434 * return v;
6435 * }
6436 * }</pre></blockquote>
6437 *
6438 * @apiNote Example:
6439 * <blockquote><pre>{@code
6440 * // implement the zip function for lists as a loop handle
6441 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6442 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6443 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6444 * zip.add(a.next());
6445 * zip.add(b.next());
6446 * return zip;
6447 * }
6448 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6449 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6450 * List<String> a = Arrays.asList("a", "b", "c", "d");
6451 * List<String> b = Arrays.asList("e", "f", "g", "h");
6452 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6453 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6454 * }</pre></blockquote>
6455 *
6456 *
6457 * @apiNote The implementation of this method can be expressed as follows:
6458 * <blockquote><pre>{@code
6459 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6460 * MethodHandle fini = (body.type().returnType() == void.class
6461 * ? null : identity(body.type().returnType()));
6462 * MethodHandle[]
6463 * checkExit = { null, null, pred, fini },
6464 * varBody = { init, body };
6465 * return loop(checkExit, varBody);
6466 * }
6467 * }</pre></blockquote>
6468 *
6469 * @param init optional initializer, providing the initial value of the loop variable.
6470 * May be {@code null}, implying a default initial value. See above for other constraints.
6471 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6472 * above for other constraints.
6473 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6474 * See above for other constraints.
6475 *
6476 * @return a method handle implementing the {@code while} loop as described by the arguments.
6477 * @throws IllegalArgumentException if the rules for the arguments are violated.
6478 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6479 *
6480 * @see #loop(MethodHandle[][])
6481 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6482 * @since 9
6483 */
6484 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6485 whileLoopChecks(init, pred, body);
6486 MethodHandle fini = identityOrVoid(body.type().returnType());
6487 MethodHandle[] checkExit = { null, null, pred, fini };
6488 MethodHandle[] varBody = { init, body };
6489 return loop(checkExit, varBody);
6490 }
6491
6492 /**
6493 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6494 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6495 * <p>
6496 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6497 * method will, in each iteration, first execute its body and then evaluate the predicate.
6498 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6499 * <p>
6500 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6501 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6502 * and updated with the value returned from its invocation. The result of loop execution will be
6503 * the final value of the additional loop-local variable (if present).
6504 * <p>
6505 * The following rules hold for these argument handles:<ul>
6506 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6507 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6508 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6509 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6510 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6511 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6512 * It will constrain the parameter lists of the other loop parts.
6513 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6514 * list {@code (A...)} is called the <em>external parameter list</em>.
6515 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6516 * additional state variable of the loop.
6517 * The body must both accept and return a value of this type {@code V}.
6518 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6519 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6520 * <a href="MethodHandles.html#effid">effectively identical</a>
6521 * to the external parameter list {@code (A...)}.
6522 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6523 * {@linkplain #empty default value}.
6524 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6525 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6526 * effectively identical to the internal parameter list.
6527 * </ul>
6528 * <p>
6529 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6530 * <li>The loop handle's result type is the result type {@code V} of the body.
6531 * <li>The loop handle's parameter types are the types {@code (A...)},
6532 * from the external parameter list.
6533 * </ul>
6534 * <p>
6535 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6536 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6537 * passed to the loop.
6538 * <blockquote><pre>{@code
6539 * V init(A...);
6540 * boolean pred(V, A...);
6541 * V body(V, A...);
6542 * V doWhileLoop(A... a...) {
6543 * V v = init(a...);
6544 * do {
6545 * v = body(v, a...);
6546 * } while (pred(v, a...));
6547 * return v;
6548 * }
6549 * }</pre></blockquote>
6550 *
6551 * @apiNote Example:
6552 * <blockquote><pre>{@code
6553 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6554 * static int zero(int limit) { return 0; }
6555 * static int step(int i, int limit) { return i + 1; }
6556 * static boolean pred(int i, int limit) { return i < limit; }
6557 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6558 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6559 * assertEquals(23, loop.invoke(23));
6560 * }</pre></blockquote>
6561 *
6562 *
6563 * @apiNote The implementation of this method can be expressed as follows:
6564 * <blockquote><pre>{@code
6565 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6566 * MethodHandle fini = (body.type().returnType() == void.class
6567 * ? null : identity(body.type().returnType()));
6568 * MethodHandle[] clause = { init, body, pred, fini };
6569 * return loop(clause);
6570 * }
6571 * }</pre></blockquote>
6572 *
6573 * @param init optional initializer, providing the initial value of the loop variable.
6574 * May be {@code null}, implying a default initial value. See above for other constraints.
6575 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6576 * See above for other constraints.
6577 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6578 * above for other constraints.
6579 *
6580 * @return a method handle implementing the {@code while} loop as described by the arguments.
6581 * @throws IllegalArgumentException if the rules for the arguments are violated.
6582 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6583 *
6584 * @see #loop(MethodHandle[][])
6585 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6586 * @since 9
6587 */
6588 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6589 whileLoopChecks(init, pred, body);
6590 MethodHandle fini = identityOrVoid(body.type().returnType());
6591 MethodHandle[] clause = {init, body, pred, fini };
6592 return loop(clause);
6593 }
6594
6595 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6596 Objects.requireNonNull(pred);
6597 Objects.requireNonNull(body);
6598 MethodType bodyType = body.type();
6599 Class<?> returnType = bodyType.returnType();
6600 List<Class<?>> innerList = bodyType.parameterList();
6601 List<Class<?>> outerList = innerList;
6602 if (returnType == void.class) {
6603 // OK
6604 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
6605 // leading V argument missing => error
6606 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6607 throw misMatchedTypes("body function", bodyType, expected);
6608 } else {
6609 outerList = innerList.subList(1, innerList.size());
6610 }
6611 MethodType predType = pred.type();
6612 if (predType.returnType() != boolean.class ||
6613 !predType.effectivelyIdenticalParameters(0, innerList)) {
6614 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6615 }
6616 if (init != null) {
6617 MethodType initType = init.type();
6618 if (initType.returnType() != returnType ||
6619 !initType.effectivelyIdenticalParameters(0, outerList)) {
6620 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6621 }
6622 }
6623 }
6624
6625 /**
6626 * Constructs a loop that runs a given number of iterations.
6627 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6628 * <p>
6629 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6630 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6631 * It will be initialized to 0 and incremented by 1 in each iteration.
6632 * <p>
6633 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6634 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6635 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6636 * <p>
6637 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6638 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6639 * iteration variable.
6640 * The result of the loop handle execution will be the final {@code V} value of that variable
6641 * (or {@code void} if there is no {@code V} variable).
6642 * <p>
6643 * The following rules hold for the argument handles:<ul>
6644 * <li>The {@code iterations} handle must not be {@code null}, and must return
6645 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6646 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6647 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6648 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6649 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6650 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6651 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6652 * of types called the <em>internal parameter list</em>.
6653 * It will constrain the parameter lists of the other loop parts.
6654 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6655 * with no additional {@code A} types, then the internal parameter list is extended by
6656 * the argument types {@code A...} of the {@code iterations} handle.
6657 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6658 * list {@code (A...)} is called the <em>external parameter list</em>.
6659 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6660 * additional state variable of the loop.
6661 * The body must both accept a leading parameter and return a value of this type {@code V}.
6662 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6663 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6664 * <a href="MethodHandles.html#effid">effectively identical</a>
6665 * to the external parameter list {@code (A...)}.
6666 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6667 * {@linkplain #empty default value}.
6668 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6669 * effectively identical to the external parameter list {@code (A...)}.
6670 * </ul>
6671 * <p>
6672 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6673 * <li>The loop handle's result type is the result type {@code V} of the body.
6674 * <li>The loop handle's parameter types are the types {@code (A...)},
6675 * from the external parameter list.
6676 * </ul>
6677 * <p>
6678 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6679 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6680 * arguments passed to the loop.
6681 * <blockquote><pre>{@code
6682 * int iterations(A...);
6683 * V init(A...);
6684 * V body(V, int, A...);
6685 * V countedLoop(A... a...) {
6686 * int end = iterations(a...);
6687 * V v = init(a...);
6688 * for (int i = 0; i < end; ++i) {
6689 * v = body(v, i, a...);
6690 * }
6691 * return v;
6692 * }
6693 * }</pre></blockquote>
6694 *
6695 * @apiNote Example with a fully conformant body method:
6696 * <blockquote><pre>{@code
6697 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6698 * // => a variation on a well known theme
6699 * static String step(String v, int counter, String init) { return "na " + v; }
6700 * // assume MH_step is a handle to the method above
6701 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6702 * MethodHandle start = MethodHandles.identity(String.class);
6703 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6704 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6705 * }</pre></blockquote>
6706 *
6707 * @apiNote Example with the simplest possible body method type,
6708 * and passing the number of iterations to the loop invocation:
6709 * <blockquote><pre>{@code
6710 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6711 * // => a variation on a well known theme
6712 * static String step(String v, int counter ) { return "na " + v; }
6713 * // assume MH_step is a handle to the method above
6714 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6715 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6716 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6717 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6718 * }</pre></blockquote>
6719 *
6720 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6721 * as loop parameters:
6722 * <blockquote><pre>{@code
6723 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6724 * // => a variation on a well known theme
6725 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6726 * // assume MH_step is a handle to the method above
6727 * MethodHandle count = MethodHandles.identity(int.class);
6728 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6729 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6730 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6731 * }</pre></blockquote>
6732 *
6733 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6734 * to enforce a loop type:
6735 * <blockquote><pre>{@code
6736 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6737 * // => a variation on a well known theme
6738 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6739 * // assume MH_step is a handle to the method above
6740 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6741 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6742 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6743 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6744 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6745 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6746 * }</pre></blockquote>
6747 *
6748 * @apiNote The implementation of this method can be expressed as follows:
6749 * <blockquote><pre>{@code
6750 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6751 * return countedLoop(empty(iterations.type()), iterations, init, body);
6752 * }
6753 * }</pre></blockquote>
6754 *
6755 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6756 * result type must be {@code int}. See above for other constraints.
6757 * @param init optional initializer, providing the initial value of the loop variable.
6758 * May be {@code null}, implying a default initial value. See above for other constraints.
6759 * @param body body of the loop, which may not be {@code null}.
6760 * It controls the loop parameters and result type in the standard case (see above for details).
6761 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6762 * and may accept any number of additional types.
6763 * See above for other constraints.
6764 *
6765 * @return a method handle representing the loop.
6766 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6767 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6768 *
6769 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6770 * @since 9
6771 */
6772 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6773 return countedLoop(empty(iterations.type()), iterations, init, body);
6774 }
6775
6776 /**
6777 * Constructs a loop that counts over a range of numbers.
6778 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6779 * <p>
6780 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
6781 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
6782 * values of the loop counter.
6783 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
6784 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
6785 * <p>
6786 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6787 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6788 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6789 * <p>
6790 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6791 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6792 * iteration variable.
6793 * The result of the loop handle execution will be the final {@code V} value of that variable
6794 * (or {@code void} if there is no {@code V} variable).
6795 * <p>
6796 * The following rules hold for the argument handles:<ul>
6797 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
6798 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
6799 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6800 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6801 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6802 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6803 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6804 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6805 * of types called the <em>internal parameter list</em>.
6806 * It will constrain the parameter lists of the other loop parts.
6807 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6808 * with no additional {@code A} types, then the internal parameter list is extended by
6809 * the argument types {@code A...} of the {@code end} handle.
6810 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6811 * list {@code (A...)} is called the <em>external parameter list</em>.
6812 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6813 * additional state variable of the loop.
6814 * The body must both accept a leading parameter and return a value of this type {@code V}.
6815 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6816 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6817 * <a href="MethodHandles.html#effid">effectively identical</a>
6818 * to the external parameter list {@code (A...)}.
6819 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6820 * {@linkplain #empty default value}.
6821 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
6822 * effectively identical to the external parameter list {@code (A...)}.
6823 * <li>Likewise, the parameter list of {@code end} must be effectively identical
6824 * to the external parameter list.
6825 * </ul>
6826 * <p>
6827 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6828 * <li>The loop handle's result type is the result type {@code V} of the body.
6829 * <li>The loop handle's parameter types are the types {@code (A...)},
6830 * from the external parameter list.
6831 * </ul>
6832 * <p>
6833 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6834 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6835 * arguments passed to the loop.
6836 * <blockquote><pre>{@code
6837 * int start(A...);
6838 * int end(A...);
6839 * V init(A...);
6840 * V body(V, int, A...);
6841 * V countedLoop(A... a...) {
6842 * int e = end(a...);
6843 * int s = start(a...);
6844 * V v = init(a...);
6845 * for (int i = s; i < e; ++i) {
6846 * v = body(v, i, a...);
6847 * }
6848 * return v;
6849 * }
6850 * }</pre></blockquote>
6851 *
6852 * @apiNote The implementation of this method can be expressed as follows:
6853 * <blockquote><pre>{@code
6854 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6855 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
6856 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
6857 * // the following semantics:
6858 * // MH_increment: (int limit, int counter) -> counter + 1
6859 * // MH_predicate: (int limit, int counter) -> counter < limit
6860 * Class<?> counterType = start.type().returnType(); // int
6861 * Class<?> returnType = body.type().returnType();
6862 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
6863 * if (returnType != void.class) { // ignore the V variable
6864 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6865 * pred = dropArguments(pred, 1, returnType); // ditto
6866 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
6867 * }
6868 * body = dropArguments(body, 0, counterType); // ignore the limit variable
6869 * MethodHandle[]
6870 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6871 * bodyClause = { init, body }, // v = init(); v = body(v, i)
6872 * indexVar = { start, incr }; // i = start(); i = i + 1
6873 * return loop(loopLimit, bodyClause, indexVar);
6874 * }
6875 * }</pre></blockquote>
6876 *
6877 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
6878 * See above for other constraints.
6879 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
6880 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
6881 * @param init optional initializer, providing the initial value of the loop variable.
6882 * May be {@code null}, implying a default initial value. See above for other constraints.
6883 * @param body body of the loop, which may not be {@code null}.
6884 * It controls the loop parameters and result type in the standard case (see above for details).
6885 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6886 * and may accept any number of additional types.
6887 * See above for other constraints.
6888 *
6889 * @return a method handle representing the loop.
6890 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
6891 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6892 *
6893 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
6894 * @since 9
6895 */
6896 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6897 countedLoopChecks(start, end, init, body);
6898 Class<?> counterType = start.type().returnType(); // int, but who's counting?
6899 Class<?> limitType = end.type().returnType(); // yes, int again
6900 Class<?> returnType = body.type().returnType();
6901 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
6902 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
6903 MethodHandle retv = null;
6904 if (returnType != void.class) {
6905 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6906 pred = dropArguments(pred, 1, returnType); // ditto
6907 retv = dropArguments(identity(returnType), 0, counterType);
6908 }
6909 body = dropArguments(body, 0, counterType); // ignore the limit variable
6910 MethodHandle[]
6911 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6912 bodyClause = { init, body }, // v = init(); v = body(v, i)
6913 indexVar = { start, incr }; // i = start(); i = i + 1
6914 return loop(loopLimit, bodyClause, indexVar);
6915 }
6916
6917 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6918 Objects.requireNonNull(start);
6919 Objects.requireNonNull(end);
6920 Objects.requireNonNull(body);
6921 Class<?> counterType = start.type().returnType();
6922 if (counterType != int.class) {
6923 MethodType expected = start.type().changeReturnType(int.class);
6924 throw misMatchedTypes("start function", start.type(), expected);
6925 } else if (end.type().returnType() != counterType) {
6926 MethodType expected = end.type().changeReturnType(counterType);
6927 throw misMatchedTypes("end function", end.type(), expected);
6928 }
6929 MethodType bodyType = body.type();
6930 Class<?> returnType = bodyType.returnType();
6931 List<Class<?>> innerList = bodyType.parameterList();
6932 // strip leading V value if present
6933 int vsize = (returnType == void.class ? 0 : 1);
6934 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
6935 // argument list has no "V" => error
6936 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6937 throw misMatchedTypes("body function", bodyType, expected);
6938 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
6939 // missing I type => error
6940 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
6941 throw misMatchedTypes("body function", bodyType, expected);
6942 }
6943 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
6944 if (outerList.isEmpty()) {
6945 // special case; take lists from end handle
6946 outerList = end.type().parameterList();
6947 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
6948 }
6949 MethodType expected = methodType(counterType, outerList);
6950 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
6951 throw misMatchedTypes("start parameter types", start.type(), expected);
6952 }
6953 if (end.type() != start.type() &&
6954 !end.type().effectivelyIdenticalParameters(0, outerList)) {
6955 throw misMatchedTypes("end parameter types", end.type(), expected);
6956 }
6957 if (init != null) {
6958 MethodType initType = init.type();
6959 if (initType.returnType() != returnType ||
6960 !initType.effectivelyIdenticalParameters(0, outerList)) {
6961 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6962 }
6963 }
6964 }
6965
6966 /**
6967 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
6968 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6969 * <p>
6970 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
6971 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
6972 * <p>
6973 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6974 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6975 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6976 * <p>
6977 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6978 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6979 * iteration variable.
6980 * The result of the loop handle execution will be the final {@code V} value of that variable
6981 * (or {@code void} if there is no {@code V} variable).
6982 * <p>
6983 * The following rules hold for the argument handles:<ul>
6984 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6985 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
6986 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6987 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
6988 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
6989 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
6990 * of types called the <em>internal parameter list</em>.
6991 * It will constrain the parameter lists of the other loop parts.
6992 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
6993 * with no additional {@code A} types, then the internal parameter list is extended by
6994 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
6995 * single type {@code Iterable} is added and constitutes the {@code A...} list.
6996 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
6997 * list {@code (A...)} is called the <em>external parameter list</em>.
6998 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6999 * additional state variable of the loop.
7000 * The body must both accept a leading parameter and return a value of this type {@code V}.
7001 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7002 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7003 * <a href="MethodHandles.html#effid">effectively identical</a>
7004 * to the external parameter list {@code (A...)}.
7005 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7006 * {@linkplain #empty default value}.
7007 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7008 * type {@code java.util.Iterator} or a subtype thereof.
7009 * The iterator it produces when the loop is executed will be assumed
7010 * to yield values which can be converted to type {@code T}.
7011 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7012 * effectively identical to the external parameter list {@code (A...)}.
7013 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7014 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7015 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7016 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7017 * the {@link MethodHandle#asType asType} conversion method.
7018 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7019 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7020 * </ul>
7021 * <p>
7022 * The type {@code T} may be either a primitive or reference.
7023 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7024 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7025 * as if by the {@link MethodHandle#asType asType} conversion method.
7026 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7027 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7028 * <p>
7029 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7030 * <li>The loop handle's result type is the result type {@code V} of the body.
7031 * <li>The loop handle's parameter types are the types {@code (A...)},
7032 * from the external parameter list.
7033 * </ul>
7034 * <p>
7035 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7036 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7037 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7038 * <blockquote><pre>{@code
7039 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7040 * V init(A...);
7041 * V body(V,T,A...);
7042 * V iteratedLoop(A... a...) {
7043 * Iterator<T> it = iterator(a...);
7044 * V v = init(a...);
7045 * while (it.hasNext()) {
7046 * T t = it.next();
7047 * v = body(v, t, a...);
7048 * }
7049 * return v;
7050 * }
7051 * }</pre></blockquote>
7052 *
7053 * @apiNote Example:
7054 * <blockquote><pre>{@code
7055 * // get an iterator from a list
7056 * static List<String> reverseStep(List<String> r, String e) {
7057 * r.add(0, e);
7058 * return r;
7059 * }
7060 * static List<String> newArrayList() { return new ArrayList<>(); }
7061 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7062 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7063 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7064 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7065 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7066 * }</pre></blockquote>
7067 *
7068 * @apiNote The implementation of this method can be expressed approximately as follows:
7069 * <blockquote><pre>{@code
7070 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7071 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7072 * Class<?> returnType = body.type().returnType();
7073 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7074 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7075 * MethodHandle retv = null, step = body, startIter = iterator;
7076 * if (returnType != void.class) {
7077 * // the simple thing first: in (I V A...), drop the I to get V
7078 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7079 * // body type signature (V T A...), internal loop types (I V A...)
7080 * step = swapArguments(body, 0, 1); // swap V <-> T
7081 * }
7082 * if (startIter == null) startIter = MH_getIter;
7083 * MethodHandle[]
7084 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7085 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7086 * return loop(iterVar, bodyClause);
7087 * }
7088 * }</pre></blockquote>
7089 *
7090 * @param iterator an optional handle to return the iterator to start the loop.
7091 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7092 * See above for other constraints.
7093 * @param init optional initializer, providing the initial value of the loop variable.
7094 * May be {@code null}, implying a default initial value. See above for other constraints.
7095 * @param body body of the loop, which may not be {@code null}.
7096 * It controls the loop parameters and result type in the standard case (see above for details).
7097 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7098 * and may accept any number of additional types.
7099 * See above for other constraints.
7100 *
7101 * @return a method handle embodying the iteration loop functionality.
7102 * @throws NullPointerException if the {@code body} handle is {@code null}.
7103 * @throws IllegalArgumentException if any argument violates the above requirements.
7104 *
7105 * @since 9
7106 */
7107 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7108 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7109 Class<?> returnType = body.type().returnType();
7110 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7111 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7112 MethodHandle startIter;
7113 MethodHandle nextVal;
7114 {
7115 MethodType iteratorType;
7116 if (iterator == null) {
7117 // derive argument type from body, if available, else use Iterable
7118 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7119 iteratorType = startIter.type().changeParameterType(0, iterableType);
7120 } else {
7121 // force return type to the internal iterator class
7122 iteratorType = iterator.type().changeReturnType(Iterator.class);
7123 startIter = iterator;
7124 }
7125 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7126 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7127
7128 // perform the asType transforms under an exception transformer, as per spec.:
7129 try {
7130 startIter = startIter.asType(iteratorType);
7131 nextVal = nextRaw.asType(nextValType);
7132 } catch (WrongMethodTypeException ex) {
7133 throw new IllegalArgumentException(ex);
7134 }
7135 }
7136
7137 MethodHandle retv = null, step = body;
7138 if (returnType != void.class) {
7139 // the simple thing first: in (I V A...), drop the I to get V
7140 retv = dropArguments(identity(returnType), 0, Iterator.class);
7141 // body type signature (V T A...), internal loop types (I V A...)
7142 step = swapArguments(body, 0, 1); // swap V <-> T
7143 }
7144
7145 MethodHandle[]
7146 iterVar = { startIter, null, hasNext, retv },
7147 bodyClause = { init, filterArgument(step, 0, nextVal) };
7148 return loop(iterVar, bodyClause);
7149 }
7150
7151 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7152 Objects.requireNonNull(body);
7153 MethodType bodyType = body.type();
7154 Class<?> returnType = bodyType.returnType();
7155 List<Class<?>> internalParamList = bodyType.parameterList();
7156 // strip leading V value if present
7157 int vsize = (returnType == void.class ? 0 : 1);
7158 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
7159 // argument list has no "V" => error
7160 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7161 throw misMatchedTypes("body function", bodyType, expected);
7162 } else if (internalParamList.size() <= vsize) {
7163 // missing T type => error
7164 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7165 throw misMatchedTypes("body function", bodyType, expected);
7166 }
7167 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7168 Class<?> iterableType = null;
7169 if (iterator != null) {
7170 // special case; if the body handle only declares V and T then
7171 // the external parameter list is obtained from iterator handle
7172 if (externalParamList.isEmpty()) {
7173 externalParamList = iterator.type().parameterList();
7174 }
7175 MethodType itype = iterator.type();
7176 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7177 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7178 }
7179 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7180 MethodType expected = methodType(itype.returnType(), externalParamList);
7181 throw misMatchedTypes("iterator parameters", itype, expected);
7182 }
7183 } else {
7184 if (externalParamList.isEmpty()) {
7185 // special case; if the iterator handle is null and the body handle
7186 // only declares V and T then the external parameter list consists
7187 // of Iterable
7188 externalParamList = Arrays.asList(Iterable.class);
7189 iterableType = Iterable.class;
7190 } else {
7191 // special case; if the iterator handle is null and the external
7192 // parameter list is not empty then the first parameter must be
7193 // assignable to Iterable
7194 iterableType = externalParamList.get(0);
7195 if (!Iterable.class.isAssignableFrom(iterableType)) {
7196 throw newIllegalArgumentException(
7197 "inferred first loop argument must inherit from Iterable: " + iterableType);
7198 }
7199 }
7200 }
7201 if (init != null) {
7202 MethodType initType = init.type();
7203 if (initType.returnType() != returnType ||
7204 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7205 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7206 }
7207 }
7208 return iterableType; // help the caller a bit
7209 }
7210
7211 /*non-public*/
7212 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7213 // there should be a better way to uncross my wires
7214 int arity = mh.type().parameterCount();
7215 int[] order = new int[arity];
7216 for (int k = 0; k < arity; k++) order[k] = k;
7217 order[i] = j; order[j] = i;
7218 Class<?>[] types = mh.type().parameterArray();
7219 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7220 MethodType swapType = methodType(mh.type().returnType(), types);
7221 return permuteArguments(mh, swapType, order);
7222 }
7223
7224 /**
7225 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7226 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7227 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7228 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7229 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7230 * {@code try-finally} handle.
7231 * <p>
7232 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7233 * The first is the exception thrown during the
7234 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7235 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7236 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7237 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7238 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7239 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7240 * <p>
7241 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7242 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7243 * two extra leading parameters:<ul>
7244 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7245 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7246 * the result from the execution of the {@code target} handle.
7247 * This parameter is not present if the {@code target} returns {@code void}.
7248 * </ul>
7249 * <p>
7250 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7251 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7252 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7253 * the cleanup.
7254 * <blockquote><pre>{@code
7255 * V target(A..., B...);
7256 * V cleanup(Throwable, V, A...);
7257 * V adapter(A... a, B... b) {
7258 * V result = (zero value for V);
7259 * Throwable throwable = null;
7260 * try {
7261 * result = target(a..., b...);
7262 * } catch (Throwable t) {
7263 * throwable = t;
7264 * throw t;
7265 * } finally {
7266 * result = cleanup(throwable, result, a...);
7267 * }
7268 * return result;
7269 * }
7270 * }</pre></blockquote>
7271 * <p>
7272 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7273 * be modified by execution of the target, and so are passed unchanged
7274 * from the caller to the cleanup, if it is invoked.
7275 * <p>
7276 * The target and cleanup must return the same type, even if the cleanup
7277 * always throws.
7278 * To create such a throwing cleanup, compose the cleanup logic
7279 * with {@link #throwException throwException},
7280 * in order to create a method handle of the correct return type.
7281 * <p>
7282 * Note that {@code tryFinally} never converts exceptions into normal returns.
7283 * In rare cases where exceptions must be converted in that way, first wrap
7284 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7285 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7286 * <p>
7287 * It is recommended that the first parameter type of {@code cleanup} be
7288 * declared {@code Throwable} rather than a narrower subtype. This ensures
7289 * {@code cleanup} will always be invoked with whatever exception that
7290 * {@code target} throws. Declaring a narrower type may result in a
7291 * {@code ClassCastException} being thrown by the {@code try-finally}
7292 * handle if the type of the exception thrown by {@code target} is not
7293 * assignable to the first parameter type of {@code cleanup}. Note that
7294 * various exception types of {@code VirtualMachineError},
7295 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7296 * thrown by almost any kind of Java code, and a finally clause that
7297 * catches (say) only {@code IOException} would mask any of the others
7298 * behind a {@code ClassCastException}.
7299 *
7300 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7301 * @param cleanup the handle that is invoked in the finally block.
7302 *
7303 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7304 * @throws NullPointerException if any argument is null
7305 * @throws IllegalArgumentException if {@code cleanup} does not accept
7306 * the required leading arguments, or if the method handle types do
7307 * not match in their return types and their
7308 * corresponding trailing parameters
7309 *
7310 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7311 * @since 9
7312 */
7313 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7314 List<Class<?>> targetParamTypes = target.type().parameterList();
7315 Class<?> rtype = target.type().returnType();
7316
7317 tryFinallyChecks(target, cleanup);
7318
7319 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7320 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7321 // target parameter list.
7322 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
7323
7324 // Ensure that the intrinsic type checks the instance thrown by the
7325 // target against the first parameter of cleanup
7326 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7327
7328 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7329 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7330 }
7331
7332 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7333 Class<?> rtype = target.type().returnType();
7334 if (rtype != cleanup.type().returnType()) {
7335 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7336 }
7337 MethodType cleanupType = cleanup.type();
7338 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7339 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7340 }
7341 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7342 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7343 }
7344 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7345 // target parameter list.
7346 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7347 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7348 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7349 cleanup.type(), target.type());
7350 }
7351 }
7352
7353 }