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.module.IllegalAccessLogger;
31 import jdk.internal.org.objectweb.asm.ClassReader;
32 import jdk.internal.org.objectweb.asm.Opcodes;
33 import jdk.internal.reflect.CallerSensitive;
34 import jdk.internal.reflect.Reflection;
35 import jdk.internal.vm.annotation.ForceInline;
36 import sun.invoke.util.ValueConversions;
37 import sun.invoke.util.VerifyAccess;
38 import sun.invoke.util.Wrapper;
39 import sun.reflect.misc.ReflectUtil;
40 import sun.security.util.SecurityConstants;
41
42 import java.lang.invoke.LambdaForm.BasicType;
43 import java.lang.reflect.Constructor;
44 import java.lang.reflect.Field;
45 import java.lang.reflect.Member;
46 import java.lang.reflect.Method;
47 import java.lang.reflect.Modifier;
48 import java.lang.reflect.ReflectPermission;
49 import java.nio.ByteOrder;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.Set;
58 import java.util.concurrent.ConcurrentHashMap;
59 import java.util.stream.Collectors;
60 import java.util.stream.Stream;
61
62 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
63 import static java.lang.invoke.MethodHandleNatives.Constants.*;
64 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
65 import static java.lang.invoke.MethodType.methodType;
66
67 /**
68 * This class consists exclusively of static methods that operate on or return
69 * method handles. They fall into several categories:
70 * <ul>
71 * <li>Lookup methods which help create method handles for methods and fields.
72 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
73 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
74 * </ul>
75 * A lookup, combinator, or factory method will fail and throw an
76 * {@code IllegalArgumentException} if the created method handle's type
77 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
78 *
79 * @author John Rose, JSR 292 EG
80 * @since 1.7
81 */
82 public class MethodHandles {
83
84 private MethodHandles() { } // do not instantiate
85
86 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
87
88 // See IMPL_LOOKUP below.
89
90 //// Method handle creation from ordinary methods.
91
92 /**
93 * Returns a {@link Lookup lookup object} with
94 * full capabilities to emulate all supported bytecode behaviors of the caller.
95 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
96 * Factory methods on the lookup object can create
97 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
98 * for any member that the caller has access to via bytecodes,
99 * including protected and private fields and methods.
100 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
101 * Do not store it in place where untrusted code can access it.
102 * <p>
103 * This method is caller sensitive, which means that it may return different
104 * values to different callers.
105 * @return a lookup object for the caller of this method, with
106 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
107 */
108 @CallerSensitive
109 @ForceInline // to ensure Reflection.getCallerClass optimization
110 public static Lookup lookup() {
111 return new Lookup(Reflection.getCallerClass());
112 }
113
114 /**
115 * This reflected$lookup method is the alternate implementation of
116 * the lookup method when being invoked by reflection.
117 */
118 @CallerSensitive
119 private static Lookup reflected$lookup() {
120 Class<?> caller = Reflection.getCallerClass();
121 if (caller.getClassLoader() == null) {
122 throw newIllegalArgumentException("illegal lookupClass: "+caller);
123 }
124 return new Lookup(caller);
125 }
126
127 /**
128 * Returns a {@link Lookup lookup object} which is trusted minimally.
129 * The lookup has the {@code UNCONDITIONAL} mode.
130 * It can only be used to create method handles to public members of
131 * public classes in packages that are exported unconditionally.
132 * <p>
133 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
134 * of this lookup object will be {@link java.lang.Object}.
135 *
136 * @apiNote The use of Object is conventional, and because the lookup modes are
137 * limited, there is no special access provided to the internals of Object, its package
138 * or its module. This public lookup object or other lookup object with
139 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
140 * is not used to determine the lookup context.
141 *
142 * <p style="font-size:smaller;">
143 * <em>Discussion:</em>
144 * The lookup class can be changed to any other class {@code C} using an expression of the form
145 * {@link Lookup#in publicLookup().in(C.class)}.
146 * A public lookup object is always subject to
147 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
148 * Also, it cannot access
149 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
150 * @return a lookup object which is trusted minimally
151 *
152 * @revised 9
153 * @spec JPMS
154 */
155 public static Lookup publicLookup() {
156 return Lookup.PUBLIC_LOOKUP;
157 }
158
159 /**
160 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
161 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
162 * The returned lookup object can provide access to classes in modules and packages,
163 * and members of those classes, outside the normal rules of Java access control,
164 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
165 * <p>
166 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
167 * allowed to do deep reflection on module {@code M2} and package of the target class
168 * if and only if all of the following conditions are {@code true}:
169 * <ul>
170 * <li>If there is a security manager, its {@code checkPermission} method is
171 * called to check {@code ReflectPermission("suppressAccessChecks")} and
172 * that must return normally.
173 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
174 * full privilege access}. Specifically:
175 * <ul>
176 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
177 * (This is because otherwise there would be no way to ensure the original lookup
178 * creator was a member of any particular module, and so any subsequent checks
179 * for readability and qualified exports would become ineffective.)
180 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
181 * (This is because an application intending to share intra-module access
182 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
183 * deep reflection to its own module.)
184 * </ul>
185 * <li>The target class must be a proper class, not a primitive or array class.
186 * (Thus, {@code M2} is well-defined.)
187 * <li>If the caller module {@code M1} differs from
188 * the target module {@code M2} then both of the following must be true:
189 * <ul>
190 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
191 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
192 * containing the target class to at least {@code M1}.</li>
193 * </ul>
194 * </ul>
195 * <p>
196 * If any of the above checks is violated, this method fails with an
197 * exception.
198 * <p>
199 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
200 * returns a {@code Lookup} on {@code targetClass} with
201 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} and
202 * {@code null} previous lookup class. The {@code ORIGINAL} mode is dropped.
203 * <p>
204 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
205 * returns a {@code Lookup} on {@code targetClass} that records
206 * the lookup class of the caller as the new previous lookup class and
207 * drops {@code MODULE} and {@code ORIGINAL} modes from the full privilege access.
208 *
209 * @param targetClass the target class
210 * @param caller the caller lookup object
211 * @return a lookup object for the target class, with private access
212 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
213 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
214 * @throws SecurityException if denied by the security manager
215 * @throws IllegalAccessException if any of the other access checks specified above fails
216 * @since 9
217 * @spec JPMS
218 * @see Lookup#dropLookupMode
219 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
220 */
221 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
222 if (caller.allowedModes == Lookup.TRUSTED) {
223 return new Lookup(targetClass);
224 }
225
226 SecurityManager sm = System.getSecurityManager();
227 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
228 if (targetClass.isPrimitive())
229 throw new IllegalArgumentException(targetClass + " is a primitive class");
230 if (targetClass.isArray())
231 throw new IllegalArgumentException(targetClass + " is an array class");
232 // Ensure that we can reason accurately about private and module access.
233 if (!caller.hasFullPrivilegeAccess())
234 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
235
236 // previous lookup class is never set if it has MODULE access
237 assert caller.previousLookupClass() == null;
238
239 Class<?> callerClass = caller.lookupClass();
240 Module callerModule = callerClass.getModule(); // M1
241 Module targetModule = targetClass.getModule(); // M2
242 Class<?> newPreviousClass = null;
243 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
244
245 if (targetModule != callerModule) {
246 if (!callerModule.canRead(targetModule))
247 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
248 if (targetModule.isNamed()) {
249 String pn = targetClass.getPackageName();
250 assert !pn.isEmpty() : "unnamed package cannot be in named module";
251 if (!targetModule.isOpen(pn, callerModule))
252 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
253 }
254
255 // M2 != M1, set previous lookup class to M1 and drop MODULE access
256 newPreviousClass = callerClass;
257 newModes &= ~Lookup.MODULE;
258 }
259
260 if (!callerModule.isNamed() && targetModule.isNamed()) {
261 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
262 if (logger != null) {
263 logger.logIfOpenedForIllegalAccess(caller, targetClass);
264 }
265 }
266 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
267 }
268
269 /**
270 * Returns the <em>class data</em> associated with the lookup class
271 * of the specified {@code Lookup} object, or {@code null}.
272 *
273 * <p> Classes can be created with class data by calling
274 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
275 * Lookup::defineHiddenClassWithClassData}.
276 * A hidden class with a class data behaves as if the hidden class
277 * has a private static final unnamed field pre-initialized with
278 * the class data and this method is equivalent as if calling
279 * {@link ConstantBootstraps#getStaticFinal(Lookup, String, Class)} to
280 * obtain the value of such field corresponding to the class data.
281 *
282 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
283 * must have {@link Lookup#ORIGINAL ORIGINAL} access in order to retrieve
284 * the class data.
285 *
286 * @apiNote
287 * This method can be called as a bootstrap method for a dynamically computed
288 * constant. A framework can create a hidden class with class data, for
289 * example that can be {@code List.of(o1, o2, o3....)} containing more than
290 * one live object. The class data is accessible only to the lookup object
291 * created by the original caller but inaccessible to other members
292 * in the same nest. If a framework passes security sensitive live objects
293 * to a hidden class via class data, it is recommended to load the value
294 * of class data as a dynamically computed constant instead of storing
295 * the live objects in private fields which are accessible to other
296 * nestmates.
297 *
298 * @param <T> the type to cast the class data object to
299 * @param caller the lookup context describing the class performing the
300 * operation (normally stacked by the JVM)
301 * @param name ignored
302 * @param type the type of the class data
303 * @return the value of the class data if present in the lookup class;
304 * otherwise {@code null}
305 * @throws IllegalAccessException if the lookup context does not have
306 * original caller access
307 * @throws ClassCastException if the class data cannot be converted to
308 * the specified {@code type}
309 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
310 * @since 15
311 */
312 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
313 if ((caller.lookupModes() & Lookup.ORIGINAL) == 0) {
314 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
315 }
316 Object classData = MethodHandleNatives.classData(caller.lookupClass);
317 return type.cast(classData);
318 }
319
320 /**
321 * Performs an unchecked "crack" of a
322 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
323 * The result is as if the user had obtained a lookup object capable enough
324 * to crack the target method handle, called
325 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
326 * on the target to obtain its symbolic reference, and then called
327 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
328 * to resolve the symbolic reference to a member.
329 * <p>
330 * If there is a security manager, its {@code checkPermission} method
331 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
332 * @param <T> the desired type of the result, either {@link Member} or a subtype
333 * @param target a direct method handle to crack into symbolic reference components
334 * @param expected a class object representing the desired result type {@code T}
335 * @return a reference to the method, constructor, or field object
336 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
337 * @throws NullPointerException if either argument is {@code null}
338 * @throws IllegalArgumentException if the target is not a direct method handle
339 * @throws ClassCastException if the member is not of the expected type
340 * @since 1.8
341 */
342 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
343 SecurityManager smgr = System.getSecurityManager();
344 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
345 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
346 return lookup.revealDirect(target).reflectAs(expected, lookup);
347 }
348 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
349 private static final java.security.Permission ACCESS_PERMISSION =
350 new ReflectPermission("suppressAccessChecks");
351
352 /**
353 * A <em>lookup object</em> is a factory for creating method handles,
354 * when the creation requires access checking.
355 * Method handles do not perform
356 * access checks when they are called, but rather when they are created.
357 * Therefore, method handle access
358 * restrictions must be enforced when a method handle is created.
359 * The caller class against which those restrictions are enforced
360 * is known as the {@linkplain #lookupClass() lookup class}.
361 * <p>
362 * A lookup class which needs to create method handles will call
363 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
364 * When the {@code Lookup} factory object is created, the identity of the lookup class is
365 * determined, and securely stored in the {@code Lookup} object.
366 * The lookup class (or its delegates) may then use factory methods
367 * on the {@code Lookup} object to create method handles for access-checked members.
368 * This includes all methods, constructors, and fields which are allowed to the lookup class,
369 * even private ones.
370 *
371 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
372 * The factory methods on a {@code Lookup} object correspond to all major
373 * use cases for methods, constructors, and fields.
374 * Each method handle created by a factory method is the functional
375 * equivalent of a particular <em>bytecode behavior</em>.
376 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
377 * the Java Virtual Machine Specification.)
378 * Here is a summary of the correspondence between these factory methods and
379 * the behavior of the resulting method handles:
380 * <table class="striped">
381 * <caption style="display:none">lookup method behaviors</caption>
382 * <thead>
383 * <tr>
384 * <th scope="col"><a id="equiv"></a>lookup expression</th>
385 * <th scope="col">member</th>
386 * <th scope="col">bytecode behavior</th>
387 * </tr>
388 * </thead>
389 * <tbody>
390 * <tr>
391 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
392 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
393 * </tr>
394 * <tr>
395 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
396 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
397 * </tr>
398 * <tr>
399 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
400 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
401 * </tr>
402 * <tr>
403 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
404 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
405 * </tr>
406 * <tr>
407 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
408 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
409 * </tr>
410 * <tr>
411 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
412 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
413 * </tr>
414 * <tr>
415 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
416 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
417 * </tr>
418 * <tr>
419 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
420 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
421 * </tr>
422 * <tr>
423 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
424 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
425 * </tr>
426 * <tr>
427 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
428 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
429 * </tr>
430 * <tr>
431 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
432 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
433 * </tr>
434 * <tr>
435 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
436 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
437 * </tr>
438 * <tr>
439 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
440 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
441 * </tr>
442 * <tr>
443 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
444 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
445 * </tr>
446 * </tbody>
447 * </table>
448 *
449 * Here, the type {@code C} is the class or interface being searched for a member,
450 * documented as a parameter named {@code refc} in the lookup methods.
451 * The method type {@code MT} is composed from the return type {@code T}
452 * and the sequence of argument types {@code A*}.
453 * The constructor also has a sequence of argument types {@code A*} and
454 * is deemed to return the newly-created object of type {@code C}.
455 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
456 * The formal parameter {@code this} stands for the self-reference of type {@code C};
457 * if it is present, it is always the leading argument to the method handle invocation.
458 * (In the case of some {@code protected} members, {@code this} may be
459 * restricted in type to the lookup class; see below.)
460 * The name {@code arg} stands for all the other method handle arguments.
461 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
462 * stands for a null reference if the accessed method or field is static,
463 * and {@code this} otherwise.
464 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
465 * for reflective objects corresponding to the given members declared in type {@code C}.
466 * <p>
467 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
468 * as if by {@code ldc CONSTANT_Class}.
469 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
470 * <p>
471 * In cases where the given member is of variable arity (i.e., a method or constructor)
472 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
473 * In all other cases, the returned method handle will be of fixed arity.
474 * <p style="font-size:smaller;">
475 * <em>Discussion:</em>
476 * The equivalence between looked-up method handles and underlying
477 * class members and bytecode behaviors
478 * can break down in a few ways:
479 * <ul style="font-size:smaller;">
480 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
481 * the lookup can still succeed, even when there is no equivalent
482 * Java expression or bytecoded constant.
483 * <li>Likewise, if {@code T} or {@code MT}
484 * is not symbolically accessible from the lookup class's loader,
485 * the lookup can still succeed.
486 * For example, lookups for {@code MethodHandle.invokeExact} and
487 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
488 * <li>If there is a security manager installed, it can forbid the lookup
489 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
490 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
491 * constant is not subject to security manager checks.
492 * <li>If the looked-up method has a
493 * <a href="MethodHandle.html#maxarity">very large arity</a>,
494 * the method handle creation may fail with an
495 * {@code IllegalArgumentException}, due to the method handle type having
496 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
497 * </ul>
498 *
499 * <h2><a id="access"></a>Access checking</h2>
500 * Access checks are applied in the factory methods of {@code Lookup},
501 * when a method handle is created.
502 * This is a key difference from the Core Reflection API, since
503 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
504 * performs access checking against every caller, on every call.
505 * <p>
506 * All access checks start from a {@code Lookup} object, which
507 * compares its recorded lookup class against all requests to
508 * create method handles.
509 * A single {@code Lookup} object can be used to create any number
510 * of access-checked method handles, all checked against a single
511 * lookup class.
512 * <p>
513 * A {@code Lookup} object can be shared with other trusted code,
514 * such as a metaobject protocol.
515 * A shared {@code Lookup} object delegates the capability
516 * to create method handles on private members of the lookup class.
517 * Even if privileged code uses the {@code Lookup} object,
518 * the access checking is confined to the privileges of the
519 * original lookup class.
520 * <p>
521 * A lookup can fail, because
522 * the containing class is not accessible to the lookup class, or
523 * because the desired class member is missing, or because the
524 * desired class member is not accessible to the lookup class, or
525 * because the lookup object is not trusted enough to access the member.
526 * In the case of a field setter function on a {@code final} field,
527 * finality enforcement is treated as a kind of access control,
528 * and the lookup will fail, except in special cases of
529 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
530 * In any of these cases, a {@code ReflectiveOperationException} will be
531 * thrown from the attempted lookup. The exact class will be one of
532 * the following:
533 * <ul>
534 * <li>NoSuchMethodException — if a method is requested but does not exist
535 * <li>NoSuchFieldException — if a field is requested but does not exist
536 * <li>IllegalAccessException — if the member exists but an access check fails
537 * </ul>
538 * <p>
539 * In general, the conditions under which a method handle may be
540 * looked up for a method {@code M} are no more restrictive than the conditions
541 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
542 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
543 * a method handle lookup will generally raise a corresponding
544 * checked exception, such as {@code NoSuchMethodException}.
545 * And the effect of invoking the method handle resulting from the lookup
546 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
547 * to executing the compiled, verified, and resolved call to {@code M}.
548 * The same point is true of fields and constructors.
549 * <p style="font-size:smaller;">
550 * <em>Discussion:</em>
551 * Access checks only apply to named and reflected methods,
552 * constructors, and fields.
553 * Other method handle creation methods, such as
554 * {@link MethodHandle#asType MethodHandle.asType},
555 * do not require any access checks, and are used
556 * independently of any {@code Lookup} object.
557 * <p>
558 * If the desired member is {@code protected}, the usual JVM rules apply,
559 * including the requirement that the lookup class must either be in the
560 * same package as the desired member, or must inherit that member.
561 * (See the Java Virtual Machine Specification, sections {@jvms
562 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
563 * In addition, if the desired member is a non-static field or method
564 * in a different package, the resulting method handle may only be applied
565 * to objects of the lookup class or one of its subclasses.
566 * This requirement is enforced by narrowing the type of the leading
567 * {@code this} parameter from {@code C}
568 * (which will necessarily be a superclass of the lookup class)
569 * to the lookup class itself.
570 * <p>
571 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
572 * that the receiver argument must match both the resolved method <em>and</em>
573 * the current class. Again, this requirement is enforced by narrowing the
574 * type of the leading parameter to the resulting method handle.
575 * (See the Java Virtual Machine Specification, section {@jmvs 4.10.1.9}.)
576 * <p>
577 * The JVM represents constructors and static initializer blocks as internal methods
578 * with special names ({@code "<init>"} and {@code "<clinit>"}).
579 * The internal syntax of invocation instructions allows them to refer to such internal
580 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
581 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
582 * <p>
583 * If the relationship between nested types is expressed directly through the
584 * {@code NestHost} and {@code NestMembers} attributes
585 * (see the Java Virtual Machine Specification, sections {@jvms
586 * 4.7.28} and {@jvms 4.7.29}),
587 * then the associated {@code Lookup} object provides direct access to
588 * the lookup class and all of its nestmates
589 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
590 * Otherwise, access between nested classes is obtained by the Java compiler creating
591 * a wrapper method to access a private method of another class in the same nest.
592 * For example, a nested class {@code C.D}
593 * can access private members within other related classes such as
594 * {@code C}, {@code C.D.E}, or {@code C.B},
595 * but the Java compiler may need to generate wrapper methods in
596 * those related classes. In such cases, a {@code Lookup} object on
597 * {@code C.E} would be unable to access those private members.
598 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
599 * which can transform a lookup on {@code C.E} into one on any of those other
600 * classes, without special elevation of privilege.
601 * <p>
602 * The accesses permitted to a given lookup object may be limited,
603 * according to its set of {@link #lookupModes lookupModes},
604 * to a subset of members normally accessible to the lookup class.
605 * For example, the {@link MethodHandles#publicLookup publicLookup}
606 * method produces a lookup object which is only allowed to access
607 * public members in public classes of exported packages.
608 * The caller sensitive method {@link MethodHandles#lookup lookup}
609 * produces a lookup object with full capabilities relative to
610 * its caller class, to emulate all supported bytecode behaviors.
611 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
612 * with fewer access modes than the original lookup object.
613 *
614 * <p style="font-size:smaller;">
615 * <a id="privacc"></a>
616 * <em>Discussion of private and module access:</em>
617 * We say that a lookup has <em>private access</em>
618 * if its {@linkplain #lookupModes lookup modes}
619 * include the possibility of accessing {@code private} members
620 * (which includes the private members of nestmates).
621 * As documented in the relevant methods elsewhere,
622 * only lookups with private access possess the following capabilities:
623 * <ul style="font-size:smaller;">
624 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
625 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
626 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
627 * for classes accessible to the lookup class
628 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
629 * within the same package member
630 * </ul>
631 * <p style="font-size:smaller;">
632 * Similarly, a lookup with module access ensures that the original lookup creator was
633 * a member in the same module as the lookup class.
634 * <p style="font-size:smaller;">
635 * Private and module access are independently determined modes; a lookup may have
636 * either or both or neither. A lookup which possesses both access modes is said to
637 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}. Such a lookup has
638 * the following additional capability:
639 * <ul style="font-size:smaller;">
640 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
641 * such as {@code Class.forName}
642 * </ul>
643 * <p style="font-size:smaller;">
644 * Each of these permissions is a consequence of the fact that a lookup object
645 * with private access can be securely traced back to an originating class,
646 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
647 * can be reliably determined and emulated by method handles.
648 *
649 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
650 * When a lookup class in one module {@code M1} accesses a class in another module
651 * {@code M2}, extra access checking is performed beyond the access mode bits.
652 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
653 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
654 * and when the type is in a package of {@code M2} that is exported to
655 * at least {@code M1}.
656 * <p>
657 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
658 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
659 * MethodHandles.privateLookupIn} methods.
660 * Teleporting across modules will always record the original lookup class as
661 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
662 * and drops {@link Lookup#MODULE MODULE} access.
663 * If the target class is in the same module as the lookup class {@code C},
664 * then the target class becomes the new lookup class
665 * and there is no change to the previous lookup class.
666 * If the target class is in a different module from {@code M1} ({@code C}'s module),
667 * {@code C} becomes the new previous lookup class
668 * and the target class becomes the new lookup class.
669 * In that case, if there was already a previous lookup class in {@code M0},
670 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
671 * drops all privileges.
672 * For example,
673 * <blockquote><pre>
674 * {@code
675 * Lookup lookup = MethodHandles.lookup(); // in class C
676 * Lookup lookup2 = lookup.in(D.class);
677 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
678 * }</pre></blockquote>
679 * <p>
680 * The {@link #lookup()} factory method produces a {@code Lookup} object
681 * with {@code null} previous lookup class.
682 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
683 * to class {@code D} without elevation of privileges.
684 * If {@code C} and {@code D} are in the same module,
685 * {@code lookup2} records {@code D} as the new lookup class and keeps the
686 * same previous lookup class as the original {@code lookup}, or
687 * {@code null} if not present.
688 * <p>
689 * When a {@code Lookup} teleports from a class
690 * in one nest to another nest, {@code PRIVATE} access is dropped.
691 * When a {@code Lookup} teleports from a class in one package to
692 * another package, {@code PACKAGE} access is dropped.
693 * When a {@code Lookup} teleports from a class in one module to another module,
694 * {@code MODULE} access is dropped.
695 * Teleporting across modules drops the ability to access non-exported classes
696 * in both the module of the new lookup class and the module of the old lookup class
697 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
698 * A {@code Lookup} can teleport back and forth to a class in the module of
699 * the lookup class and the module of the previous class lookup.
700 * Teleporting across modules can only decrease access but cannot increase it.
701 * Teleporting to some third module drops all accesses.
702 * <p>
703 * In the above example, if {@code C} and {@code D} are in different modules,
704 * {@code lookup2} records {@code D} as its lookup class and
705 * {@code C} as its previous lookup class and {@code lookup2} has only
706 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
707 * {@code C}'s module and {@code D}'s module.
708 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
709 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
710 * class {@code D} is recorded as its previous lookup class.
711 * <p>
712 * Teleporting across modules restricts access to the public types that
713 * both the lookup class and the previous lookup class can equally access
714 * (see below).
715 * <p>
716 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
717 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
718 * and create a new {@code Lookup} with <a href="#privacc">private access</a>
719 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
720 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
721 * to call {@code privateLookupIn}.
722 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
723 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
724 * produces a new {@code Lookup} on {@code T} with full capabilities.
725 * A {@code lookup} on {@code C} is also allowed
726 * to do deep reflection on {@code T} in another module {@code M2} if
727 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
728 * the package containing {@code T} to at least {@code M1}.
729 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
730 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
731 * The resulting {@code Lookup} can be used to do member lookup or teleport
732 * to another lookup class by calling {@link #in Lookup::in}. But
733 * it cannot be used to obtain another private {@code Lookup} by calling
734 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
735 * because it has no {@code MODULE} access.
736 *
737 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
738 *
739 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
740 * allows cross-module access. The access checking is performed with respect
741 * to both the lookup class and the previous lookup class if present.
742 * <p>
743 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
744 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
745 * exported unconditionally}.
746 * <p>
747 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
748 * the lookup with {@link #PUBLIC} mode can access all public types in modules
749 * that are readable to {@code M1} and the type is in a package that is exported
750 * at least to {@code M1}.
751 * <p>
752 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
753 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
754 * the intersection of all public types that are accessible to {@code M1}
755 * with all public types that are accessible to {@code M0}. {@code M0}
756 * reads {@code M1} and hence the set of accessible types includes:
757 *
758 * <table class="striped">
759 * <caption style="display:none">
760 * Public types in the following packages are accessible to the
761 * lookup class and the previous lookup class.
762 * </caption>
763 * <thead>
764 * <tr>
765 * <th scope="col">Equally accessible types to {@code M0} and {@code M1}</th>
766 * </tr>
767 * </thead>
768 * <tbody>
769 * <tr>
770 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M1}</th>
771 * </tr>
772 * <tr>
773 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</th>
774 * </tr>
775 * <tr>
776 * <th scope="row" style="text-align:left">unconditional-exported packages from a third module {@code M2}
777 * if both {@code M0} and {@code M1} read {@code M2}</th>
778 * </tr>
779 * <tr>
780 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M1} to {@code M0}</th>
781 * </tr>
782 * <tr>
783 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M0} to {@code M1}
784 * if {@code M1} reads {@code M0}</th>
785 * </tr>
786 * <tr>
787 * <th scope="row" style="text-align:left">qualified-exported packages from a third module {@code M2} to
788 * both {@code M0} and {@code M1} if both {@code M0} and {@code M1} read {@code M2}</th>
789 * </tr>
790 * </tbody>
791 * </table>
792 *
793 * <h2><a id="access-modes"></a>Access modes</h2>
794 *
795 * The table below shows the access modes of a {@code Lookup} produced by
796 * any of the following factory or transformation methods:
797 * <ul>
798 * <li>{@link #lookup() MethodHandles.lookup()}</li>
799 * <li>{@link #publicLookup() MethodHandles.publicLookup()}</li>
800 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn}</li>
801 * <li>{@link Lookup#in}</li>
802 * <li>{@link Lookup#dropLookupMode(int)}</li>
803 * </ul>
804 *
805 * <table class="striped">
806 * <caption style="display:none">
807 * Access mode summary
808 * </caption>
809 * <thead>
810 * <tr>
811 * <th scope="col">Lookup object</th>
812 * <th style="text-align:center">original</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">ORI</td>
824 * <td style="text-align:center">PRO</td>
825 * <td style="text-align:center">PRI</td>
826 * <td style="text-align:center">PAC</td>
827 * <td style="text-align:center">MOD</td>
828 * <td style="text-align:center">1R</td>
829 * </tr>
830 * <tr>
831 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
832 * <td></td>
833 * <td></td>
834 * <td></td>
835 * <td style="text-align:center">PAC</td>
836 * <td style="text-align:center">MOD</td>
837 * <td style="text-align:center">1R</td>
838 * </tr>
839 * <tr>
840 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
841 * <td></td>
842 * <td></td>
843 * <td></td>
844 * <td></td>
845 * <td style="text-align:center">MOD</td>
846 * <td style="text-align:center">1R</td>
847 * </tr>
848 * <tr>
849 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
850 * <td></td>
851 * <td></td>
852 * <td></td>
853 * <td></td>
854 * <td></td>
855 * <td style="text-align:center">2R</td>
856 * </tr>
857 * <tr>
858 * <td>{@code CL.in(D).in(C)} hop back to module</td>
859 * <td></td>
860 * <td></td>
861 * <td></td>
862 * <td></td>
863 * <td></td>
864 * <td style="text-align:center">2R</td>
865 * </tr>
866 * <tr>
867 * <td>{@code PRI1 = privateLookupIn(C1,CL)}</td>
868 * <td></td>
869 * <td style="text-align:center">PRO</td>
870 * <td style="text-align:center">PRI</td>
871 * <td style="text-align:center">PAC</td>
872 * <td style="text-align:center">MOD</td>
873 * <td style="text-align:center">1R</td>
874 * </tr>
875 * <tr>
876 * <td>{@code PRI1a = privateLookupIn(C,PRI1)}</td>
877 * <td></td>
878 * <td style="text-align:center">PRO</td>
879 * <td style="text-align:center">PRI</td>
880 * <td style="text-align:center">PAC</td>
881 * <td style="text-align:center">MOD</td>
882 * <td style="text-align:center">1R</td>
883 * </tr>
884 * <tr>
885 * <td>{@code PRI1.in(C1)} same package</td>
886 * <td></td>
887 * <td></td>
888 * <td></td>
889 * <td style="text-align:center">PAC</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(C1)} different package</td>
895 * <td></td>
896 * <td></td>
897 * <td></td>
898 * <td></td>
899 * <td style="text-align:center">MOD</td>
900 * <td style="text-align:center">1R</td>
901 * </tr>
902 * <tr>
903 * <td>{@code PRI1.in(D)} different module</td>
904 * <td></td>
905 * <td></td>
906 * <td></td>
907 * <td></td>
908 * <td></td>
909 * <td style="text-align:center">2R</td>
910 * </tr>
911 * <tr>
912 * <td>{@code PRI1.dropLookupMode(PROTECTED)}</td>
913 * <td></td>
914 * <td></td>
915 * <td style="text-align:center">PRI</td>
916 * <td style="text-align:center">PAC</td>
917 * <td style="text-align:center">MOD</td>
918 * <td style="text-align:center">1R</td>
919 * </tr>
920 * <tr>
921 * <td>{@code PRI1.dropLookupMode(PRIVATE)}</td>
922 * <td></td>
923 * <td></td>
924 * <td></td>
925 * <td style="text-align:center">PAC</td>
926 * <td style="text-align:center">MOD</td>
927 * <td style="text-align:center">1R</td>
928 * </tr>
929 * <tr>
930 * <td>{@code PRI1.dropLookupMode(PACKAGE)}</td>
931 * <td></td>
932 * <td></td>
933 * <td></td>
934 * <td></td>
935 * <td style="text-align:center">MOD</td>
936 * <td style="text-align:center">1R</td>
937 * </tr>
938 * <tr>
939 * <td>{@code PRI1.dropLookupMode(MODULE)}</td>
940 * <td></td>
941 * <td></td>
942 * <td></td>
943 * <td></td>
944 * <td></td>
945 * <td style="text-align:center">1R</td>
946 * </tr>
947 * <tr>
948 * <td>{@code PRI1.dropLookupMode(PUBLIC)}</td>
949 * <td></td>
950 * <td></td>
951 * <td></td>
952 * <td></td>
953 * <td></td>
954 * <td style="text-align:center">none</td>
955 * <tr>
956 * <td>{@code PRI2 = privateLookupIn(D,CL)}</td>
957 * <td></td>
958 * <td style="text-align:center">PRO</td>
959 * <td style="text-align:center">PRI</td>
960 * <td style="text-align:center">PAC</td>
961 * <td></td>
962 * <td style="text-align:center">2R</td>
963 * </tr>
964 * <tr>
965 * <td>{@code privateLookupIn(D,PRI1)}</td>
966 * <td></td>
967 * <td style="text-align:center">PRO</td>
968 * <td style="text-align:center">PRI</td>
969 * <td style="text-align:center">PAC</td>
970 * <td></td>
971 * <td style="text-align:center">2R</td>
972 * </tr>
973 * <tr>
974 * <td>{@code privateLookupIn(C,PRI2)} fails</td>
975 * <td></td>
976 * <td></td>
977 * <td></td>
978 * <td></td>
979 * <td></td>
980 * <td style="text-align:center">IAE</td>
981 * </tr>
982 * <tr>
983 * <td>{@code PRI2.in(D2)} same package</td>
984 * <td></td>
985 * <td></td>
986 * <td></td>
987 * <td style="text-align:center">PAC</td>
988 * <td></td>
989 * <td style="text-align:center">2R</td>
990 * </tr>
991 * <tr>
992 * <td>{@code PRI2.in(D2)} different package</td>
993 * <td></td>
994 * <td></td>
995 * <td></td>
996 * <td></td>
997 * <td></td>
998 * <td style="text-align:center">2R</td>
999 * </tr>
1000 * <tr>
1001 * <td>{@code PRI2.in(C1)} hop back to module</td>
1002 * <td></td>
1003 * <td></td>
1004 * <td></td>
1005 * <td></td>
1006 * <td></td>
1007 * <td style="text-align:center">2R</td>
1008 * </tr>
1009 * <tr>
1010 * <td>{@code PRI2.in(E)} hop to third module</td>
1011 * <td></td>
1012 * <td></td>
1013 * <td></td>
1014 * <td></td>
1015 * <td></td>
1016 * <td style="text-align:center">none</td>
1017 * </tr>
1018 * <tr>
1019 * <td>{@code PRI2.dropLookupMode(PROTECTED)}</td>
1020 * <td></td>
1021 * <td></td>
1022 * <td style="text-align:center">PRI</td>
1023 * <td style="text-align:center">PAC</td>
1024 * <td></td>
1025 * <td style="text-align:center">2R</td>
1026 * </tr>
1027 * <tr>
1028 * <td>{@code PRI2.dropLookupMode(PRIVATE)}</td>
1029 * <td></td>
1030 * <td></td>
1031 * <td></td>
1032 * <td style="text-align:center">PAC</td>
1033 * <td></td>
1034 * <td style="text-align:center">2R</td>
1035 * </tr>
1036 * <tr>
1037 * <td>{@code PRI2.dropLookupMode(PACKAGE)}</td>
1038 * <td></td>
1039 * <td></td>
1040 * <td></td>
1041 * <td></td>
1042 * <td></td>
1043 * <td style="text-align:center">2R</td>
1044 * </tr>
1045 * <tr>
1046 * <td>{@code PRI2.dropLookupMode(MODULE)}</td>
1047 * <td></td>
1048 * <td></td>
1049 * <td></td>
1050 * <td></td>
1051 * <td></td>
1052 * <td style="text-align:center">2R</td>
1053 * </tr>
1054 * <tr>
1055 * <td>{@code PRI2.dropLookupMode(PUBLIC)}</td>
1056 * <td></td>
1057 * <td></td>
1058 * <td></td>
1059 * <td></td>
1060 * <td></td>
1061 * <td style="text-align:center">none</td>
1062 * </tr>
1063 * <tr>
1064 * <td>{@code CL.dropLookupMode(PROTECTED)}</td>
1065 * <td></td>
1066 * <td></td>
1067 * <td style="text-align:center">PRI</td>
1068 * <td style="text-align:center">PAC</td>
1069 * <td style="text-align:center">MOD</td>
1070 * <td style="text-align:center">1R</td>
1071 * </tr>
1072 * <tr>
1073 * <td>{@code CL.dropLookupMode(PRIVATE)}</td>
1074 * <td></td>
1075 * <td></td>
1076 * <td></td>
1077 * <td style="text-align:center">PAC</td>
1078 * <td style="text-align:center">MOD</td>
1079 * <td style="text-align:center">1R</td>
1080 * </tr>
1081 * <tr>
1082 * <td>{@code CL.dropLookupMode(PACKAGE)}</td>
1083 * <td></td>
1084 * <td></td>
1085 * <td></td>
1086 * <td></td>
1087 * <td style="text-align:center">MOD</td>
1088 * <td style="text-align:center">1R</td>
1089 * </tr>
1090 * <tr>
1091 * <td>{@code CL.dropLookupMode(MODULE)}</td>
1092 * <td></td>
1093 * <td></td>
1094 * <td></td>
1095 * <td></td>
1096 * <td></td>
1097 * <td style="text-align:center">1R</td>
1098 * </tr>
1099 * <tr>
1100 * <td>{@code CL.dropLookupMode(PUBLIC)}</td>
1101 * <td></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 PUB = publicLookup()}</td>
1110 * <td></td>
1111 * <td></td>
1112 * <td></td>
1113 * <td></td>
1114 * <td></td>
1115 * <td style="text-align:center">U</td>
1116 * </tr>
1117 * <tr>
1118 * <td>{@code PUB.in(D)} different module</td>
1119 * <td></td>
1120 * <td></td>
1121 * <td></td>
1122 * <td></td>
1123 * <td></td>
1124 * <td style="text-align:center">U</td>
1125 * </tr>
1126 * <tr>
1127 * <td>{@code PUB.in(D).in(E)} third module</td>
1128 * <td></td>
1129 * <td></td>
1130 * <td></td>
1131 * <td></td>
1132 * <td></td>
1133 * <td style="text-align:center">U</td>
1134 * </tr>
1135 * <tr>
1136 * <td>{@code PUB.dropLookupMode(UNCONDITIONAL)}</td>
1137 * <td></td>
1138 * <td></td>
1139 * <td></td>
1140 * <td></td>
1141 * <td></td>
1142 * <td style="text-align:center">none</td>
1143 * </tr>
1144 * <tr>
1145 * <td>{@code privateLookupIn(C1,PUB)} fails</td>
1146 * <td></td>
1147 * <td></td>
1148 * <td></td>
1149 * <td></td>
1150 * <td></td>
1151 * <td style="text-align:center">IAE</td>
1152 * </tr>
1153 * <tr>
1154 * <td>{@code ANY.in(X)}, for inaccessible {@code X}</td>
1155 * <td></td>
1156 * <td></td>
1157 * <td></td>
1158 * <td></td>
1159 * <td></td>
1160 * <td style="text-align:center">none</td>
1161 * </tr>
1162 * </tbody>
1163 * </table>
1164 *
1165 * <p>
1166 * Notes:
1167 * <ul>
1168 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1169 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1170 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1171 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1172 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1173 * {@code PRO} indicates {@link #PROTECTED} bit set,
1174 * {@code PRI} indicates {@link #PRIVATE} bit set,
1175 * {@code PAC} indicates {@link #PACKAGE} bit set,
1176 * {@code MOD} indicates {@link #MODULE} bit set,
1177 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1178 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1179 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1180 * <li>Public access comes in three kinds:
1181 * <ul>
1182 * <li>unconditional ({@code U}): the lookup assumes readability.
1183 * The lookup has {@code null} previous lookup class.
1184 * <li>one-module-reads ({@code 1R}): the module access checking is
1185 * performed with respect to the lookup class. The lookup has {@code null}
1186 * previous lookup class.
1187 * <li>two-module-reads ({@code 2R}): the module access checking is
1188 * performed with respect to the lookup class and the previous lookup class.
1189 * The lookup has a non-null previous lookup class which is in a
1190 * different module from the current lookup class.
1191 * </ul>
1192 * <li>Any attempt to reach a third module loses all access.</li>
1193 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1194 * all access modes are dropped.</li>
1195 * </ul>
1196 *
1197 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1198 * Although bytecode instructions can only refer to classes in
1199 * a related class loader, this API can search for methods in any
1200 * class, as long as a reference to its {@code Class} object is
1201 * available. Such cross-loader references are also possible with the
1202 * Core Reflection API, and are impossible to bytecode instructions
1203 * such as {@code invokestatic} or {@code getfield}.
1204 * There is a {@linkplain java.lang.SecurityManager security manager API}
1205 * to allow applications to check such cross-loader references.
1206 * These checks apply to both the {@code MethodHandles.Lookup} API
1207 * and the Core Reflection API
1208 * (as found on {@link java.lang.Class Class}).
1209 * <p>
1210 * If a security manager is present, member and class lookups are subject to
1211 * additional checks.
1212 * From one to three calls are made to the security manager.
1213 * Any of these calls can refuse access by throwing a
1214 * {@link java.lang.SecurityException SecurityException}.
1215 * Define {@code smgr} as the security manager,
1216 * {@code lookc} as the lookup class of the current lookup object,
1217 * {@code refc} as the containing class in which the member
1218 * is being sought, and {@code defc} as the class in which the
1219 * member is actually defined.
1220 * (If a class or other type is being accessed,
1221 * the {@code refc} and {@code defc} values are the class itself.)
1222 * The value {@code lookc} is defined as <em>not present</em>
1223 * if the current lookup object does not have
1224 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1225 * The calls are made according to the following rules:
1226 * <ul>
1227 * <li><b>Step 1:</b>
1228 * If {@code lookc} is not present, or if its class loader is not
1229 * the same as or an ancestor of the class loader of {@code refc},
1230 * then {@link SecurityManager#checkPackageAccess
1231 * smgr.checkPackageAccess(refcPkg)} is called,
1232 * where {@code refcPkg} is the package of {@code refc}.
1233 * <li><b>Step 2a:</b>
1234 * If the retrieved member is not public and
1235 * {@code lookc} is not present, then
1236 * {@link SecurityManager#checkPermission smgr.checkPermission}
1237 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1238 * <li><b>Step 2b:</b>
1239 * If the retrieved class has a {@code null} class loader,
1240 * and {@code lookc} is not present, then
1241 * {@link SecurityManager#checkPermission smgr.checkPermission}
1242 * with {@code RuntimePermission("getClassLoader")} is called.
1243 * <li><b>Step 3:</b>
1244 * If the retrieved member is not public,
1245 * and if {@code lookc} is not present,
1246 * and if {@code defc} and {@code refc} are different,
1247 * then {@link SecurityManager#checkPackageAccess
1248 * smgr.checkPackageAccess(defcPkg)} is called,
1249 * where {@code defcPkg} is the package of {@code defc}.
1250 * </ul>
1251 * Security checks are performed after other access checks have passed.
1252 * Therefore, the above rules presuppose a member or class that is public,
1253 * or else that is being accessed from a lookup class that has
1254 * rights to access the member or class.
1255 * <p>
1256 * If a security manager is present and the current lookup object does not have
1257 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1258 * {@link #defineClass(byte[]) defineClass}
1259 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1260 * with {@code RuntimePermission("defineClass")}.
1261 *
1262 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1263 * A small number of Java methods have a special property called caller sensitivity.
1264 * A <em>caller-sensitive</em> method can behave differently depending on the
1265 * identity of its immediate caller.
1266 * <p>
1267 * If a method handle for a caller-sensitive method is requested,
1268 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1269 * but they take account of the lookup class in a special way.
1270 * The resulting method handle behaves as if it were called
1271 * from an instruction contained in the lookup class,
1272 * so that the caller-sensitive method detects the lookup class.
1273 * (By contrast, the invoker of the method handle is disregarded.)
1274 * Thus, in the case of caller-sensitive methods,
1275 * different lookup classes may give rise to
1276 * differently behaving method handles.
1277 * <p>
1278 * In cases where the lookup object is
1279 * {@link MethodHandles#publicLookup() publicLookup()},
1280 * or some other lookup object without the
1281 * {@linkplain #hasFullPrivilegeAccess() full privilege access},
1282 * the lookup class is disregarded.
1283 * In such cases, no caller-sensitive method handle can be created,
1284 * access is forbidden, and the lookup fails with an
1285 * {@code IllegalAccessException}.
1286 * <p style="font-size:smaller;">
1287 * <em>Discussion:</em>
1288 * For example, the caller-sensitive method
1289 * {@link java.lang.Class#forName(String) Class.forName(x)}
1290 * can return varying classes or throw varying exceptions,
1291 * depending on the class loader of the class that calls it.
1292 * A public lookup of {@code Class.forName} will fail, because
1293 * there is no reasonable way to determine its bytecode behavior.
1294 * <p style="font-size:smaller;">
1295 * If an application caches method handles for broad sharing,
1296 * it should use {@code publicLookup()} to create them.
1297 * If there is a lookup of {@code Class.forName}, it will fail,
1298 * and the application must take appropriate action in that case.
1299 * It may be that a later lookup, perhaps during the invocation of a
1300 * bootstrap method, can incorporate the specific identity
1301 * of the caller, making the method accessible.
1302 * <p style="font-size:smaller;">
1303 * The function {@code MethodHandles.lookup} is caller sensitive
1304 * so that there can be a secure foundation for lookups.
1305 * Nearly all other methods in the JSR 292 API rely on lookup
1306 * objects to check access requests.
1307 *
1308 * @revised 9
1309 */
1310 public static final
1311 class Lookup {
1312 /** The class on behalf of whom the lookup is being performed. */
1313 private final Class<?> lookupClass;
1314
1315 /** previous lookup class */
1316 private final Class<?> prevLookupClass;
1317
1318 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1319 private final int allowedModes;
1320
1321 static {
1322 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1323 }
1324
1325 /** A single-bit mask representing {@code public} access,
1326 * which may contribute to the result of {@link #lookupModes lookupModes}.
1327 * The value, {@code 0x01}, happens to be the same as the value of the
1328 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1329 * <p>
1330 * A {@code Lookup} with this lookup mode performs cross-module access check
1331 * with respect to the {@linkplain #lookupClass() lookup class} and
1332 * {@linkplain #previousLookupClass() previous lookup class} if present.
1333 */
1334 public static final int PUBLIC = Modifier.PUBLIC;
1335
1336 /** A single-bit mask representing {@code private} access,
1337 * which may contribute to the result of {@link #lookupModes lookupModes}.
1338 * The value, {@code 0x02}, happens to be the same as the value of the
1339 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1340 */
1341 public static final int PRIVATE = Modifier.PRIVATE;
1342
1343 /** A single-bit mask representing {@code protected} access,
1344 * which may contribute to the result of {@link #lookupModes lookupModes}.
1345 * The value, {@code 0x04}, happens to be the same as the value of the
1346 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1347 */
1348 public static final int PROTECTED = Modifier.PROTECTED;
1349
1350 /** A single-bit mask representing {@code package} access (default access),
1351 * which may contribute to the result of {@link #lookupModes lookupModes}.
1352 * The value is {@code 0x08}, which does not correspond meaningfully to
1353 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1354 */
1355 public static final int PACKAGE = Modifier.STATIC;
1356
1357 /** A single-bit mask representing {@code module} access,
1358 * which may contribute to the result of {@link #lookupModes lookupModes}.
1359 * The value is {@code 0x10}, which does not correspond meaningfully to
1360 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1361 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1362 * with this lookup mode can access all public types in the module of the
1363 * lookup class and public types in packages exported by other modules
1364 * to the module of the lookup class.
1365 * <p>
1366 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1367 * previous lookup class} is always {@code null}.
1368 *
1369 * @since 9
1370 * @spec JPMS
1371 */
1372 public static final int MODULE = PACKAGE << 1;
1373
1374 /** A single-bit mask representing {@code unconditional} access
1375 * which may contribute to the result of {@link #lookupModes lookupModes}.
1376 * The value is {@code 0x20}, which does not correspond meaningfully to
1377 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1378 * A {@code Lookup} with this lookup mode assumes {@linkplain
1379 * java.lang.Module#canRead(java.lang.Module) readability}.
1380 * This lookup mode can access all public members of public types
1381 * of all modules when the type is in a package that is {@link
1382 * java.lang.Module#isExported(String) exported unconditionally}.
1383 *
1384 * <p>
1385 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1386 * previous lookup class} is always {@code null}.
1387 *
1388 * @since 9
1389 * @spec JPMS
1390 * @see #publicLookup()
1391 */
1392 public static final int UNCONDITIONAL = PACKAGE << 2;
1393
1394
1395 /** A single-bit mask representing {@code original} full privilege access
1396 * which may contribute to the result of {@link #lookupModes lookupModes}.
1397 * The value is {@code 0x40}, which does not correspond meaningfully to
1398 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1399 *
1400 * <p>
1401 * If this lookup mode is set, the {@code Lookup} object must be
1402 * created by the original lookup class by calling
1403 * {@link MethodHandles#lookup()} method or by a bootstrap method
1404 * invoked by the VM.
1405 *
1406 * @since 14
1407 */
1408 public static final int ORIGINAL = PACKAGE << 3;
1409
1410 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1411 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
1412 private static final int TRUSTED = -1;
1413
1414 /*
1415 * Adjust PUBLIC => PUBLIC|MODULE|UNCONDITIONAL
1416 * Adjust 0 => PACKAGE
1417 */
1418 private static int fixmods(int mods) {
1419 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL - ORIGINAL);
1420 if (Modifier.isPublic(mods))
1421 mods |= UNCONDITIONAL;
1422 return (mods != 0) ? mods : PACKAGE;
1423 }
1424
1425 /** Tells which class is performing the lookup. It is this class against
1426 * which checks are performed for visibility and access permissions.
1427 * <p>
1428 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1429 * access checks are performed against both the lookup class and the previous lookup class.
1430 * <p>
1431 * The class implies a maximum level of access permission,
1432 * but the permissions may be additionally limited by the bitmask
1433 * {@link #lookupModes lookupModes}, which controls whether non-public members
1434 * can be accessed.
1435 * @return the lookup class, on behalf of which this lookup object finds members
1436 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1437 */
1438 public Class<?> lookupClass() {
1439 return lookupClass;
1440 }
1441
1442 /** Reports a lookup class in another module that this lookup object
1443 * was previously teleported from, or {@code null}.
1444 * <p>
1445 * A {@code Lookup} object produced by the factory methods, such as the
1446 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1447 * has {@code null} previous lookup class.
1448 * A {@code Lookup} object has a non-null previous lookup class
1449 * when this lookup was teleported from an old lookup class
1450 * in one module to a new lookup class in another module.
1451 *
1452 * @return the lookup class in another module that this lookup object was
1453 * previously teleported from, or {@code null}
1454 * @since 14
1455 * @see #in(Class)
1456 * @see MethodHandles#privateLookupIn(Class, Lookup)
1457 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1458 */
1459 public Class<?> previousLookupClass() {
1460 return prevLookupClass;
1461 }
1462
1463 // This is just for calling out to MethodHandleImpl.
1464 private Class<?> lookupClassOrNull() {
1465 if (allowedModes == TRUSTED) {
1466 return null;
1467 }
1468 if (allowedModes == UNCONDITIONAL) {
1469 // use Object as the caller to pass to VM doing resolution
1470 return Object.class;
1471 }
1472 return lookupClass;
1473 }
1474
1475 /** Tells which access-protection classes of members this lookup object can produce.
1476 * The result is a bit-mask of the bits
1477 * {@linkplain #PUBLIC PUBLIC (0x01)},
1478 * {@linkplain #PRIVATE PRIVATE (0x02)},
1479 * {@linkplain #PROTECTED PROTECTED (0x04)},
1480 * {@linkplain #PACKAGE PACKAGE (0x08)},
1481 * {@linkplain #MODULE MODULE (0x10)},
1482 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1483 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1484 * <p>
1485 * A freshly-created lookup object
1486 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1487 * all possible bits set, except {@code UNCONDITIONAL}.
1488 * A lookup object on a new lookup class
1489 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1490 * may have some mode bits set to zero.
1491 * Mode bits can also be
1492 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1493 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1494 * The purpose of this is to restrict access via the new lookup object,
1495 * so that it can access only names which can be reached by the original
1496 * lookup object, and also by the new lookup class.
1497 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1498 * @see #in
1499 * @see #dropLookupMode
1500 *
1501 * @revised 9
1502 * @spec JPMS
1503 */
1504 public int lookupModes() {
1505 return allowedModes & ALL_MODES;
1506 }
1507
1508 /** Embody the current class (the lookupClass) as a lookup class
1509 * for method handle creation.
1510 * Must be called by from a method in this package,
1511 * which in turn is called by a method not in this package.
1512 */
1513 Lookup(Class<?> lookupClass) {
1514 this(lookupClass, null, FULL_POWER_MODES);
1515 }
1516
1517 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1518 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1519 && prevLookupClass.getModule() != lookupClass.getModule());
1520 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1521 this.lookupClass = lookupClass;
1522 this.prevLookupClass = prevLookupClass;
1523 this.allowedModes = allowedModes;
1524 }
1525
1526 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1527 // make sure we haven't accidentally picked up a privileged class:
1528 checkUnprivilegedlookupClass(lookupClass);
1529 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1530 }
1531
1532 /**
1533 * Creates a lookup on the specified new lookup class.
1534 * The resulting object will report the specified
1535 * class as its own {@link #lookupClass() lookupClass}.
1536 *
1537 * <p>
1538 * However, the resulting {@code Lookup} object is guaranteed
1539 * to have no more access capabilities than the original.
1540 * In particular, access capabilities can be lost as follows:<ul>
1541 * <li>If the new lookup class is in a different module from the old one,
1542 * i.e. {@link #MODULE MODULE} access is lost.
1543 * <li>If the new lookup class is in a different package
1544 * than the old one, protected and default (package) members will not be accessible,
1545 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1546 * <li>If the new lookup class is not within the same package member
1547 * as the old one, private members will not be accessible, and protected members
1548 * will not be accessible by virtue of inheritance,
1549 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1550 * (Protected members may continue to be accessible because of package sharing.)
1551 * <li>If the new lookup class is different from the old lookup class,
1552 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1553 * <li>If the new lookup class is not
1554 * {@linkplain #accessClass(Class) accessible} to this lookup,
1555 * then no members, not even public members, will be accessible
1556 * i.e. all access modes are lost.
1557 * <li>If the new lookup class, the old lookup class and the previous lookup class
1558 * are all in different modules i.e. teleporting to a third module,
1559 * all access modes are lost.
1560 * </ul>
1561 * <p>
1562 * The new previous lookup class is chosen as follows:
1563 * <ul>
1564 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1565 * the new previous lookup class is {@code null}.
1566 * <li>If the new lookup class is in the same module as the old lookup class,
1567 * the new previous lookup class is the old previous lookup class.
1568 * <li>If the new lookup class is in a different module from the old lookup class,
1569 * the new previous lookup class is the old lookup class.
1570 *</ul>
1571 * <p>
1572 * The resulting lookup's capabilities for loading classes
1573 * (used during {@link #findClass} invocations)
1574 * are determined by the lookup class' loader,
1575 * which may change due to this operation.
1576 * <p>
1577 * @param requestedLookupClass the desired lookup class for the new lookup object
1578 * @return a lookup object which reports the desired lookup class, or the same object
1579 * if there is no change
1580 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1581 * @throws NullPointerException if the argument is null
1582 *
1583 * @revised 9
1584 * @spec JPMS
1585 * @see #accessClass(Class)
1586 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1587 */
1588 public Lookup in(Class<?> requestedLookupClass) {
1589 Objects.requireNonNull(requestedLookupClass);
1590 if (requestedLookupClass.isPrimitive())
1591 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1592 if (requestedLookupClass.isArray())
1593 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1594
1595 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1596 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1597 if (requestedLookupClass == this.lookupClass)
1598 return this; // keep same capabilities
1599 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1600 Module fromModule = this.lookupClass.getModule();
1601 Module targetModule = requestedLookupClass.getModule();
1602 Class<?> plc = this.previousLookupClass();
1603 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1604 assert plc == null;
1605 newModes = UNCONDITIONAL;
1606 } else if (fromModule != targetModule) {
1607 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1608 // allow hopping back and forth between fromModule and plc's module
1609 // but not the third module
1610 newModes = 0;
1611 }
1612 // drop MODULE access
1613 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1614 // teleport from this lookup class
1615 plc = this.lookupClass;
1616 }
1617 if ((newModes & PACKAGE) != 0
1618 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1619 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1620 }
1621 // Allow nestmate lookups to be created without special privilege:
1622 if ((newModes & PRIVATE) != 0
1623 && !this.lookupClass.isNestmateOf(requestedLookupClass)
1624 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1625 newModes &= ~(PRIVATE|PROTECTED);
1626 }
1627 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1628 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1629 // The requested class it not accessible from the lookup class.
1630 // No permissions.
1631 newModes = 0;
1632 }
1633 return newLookup(requestedLookupClass, plc, newModes);
1634 }
1635
1636 /**
1637 * Creates a lookup on the same lookup class which this lookup object
1638 * finds members, but with a lookup mode that has lost the given lookup mode.
1639 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1640 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
1641 * {@link #PROTECTED PROTECTED} and and {@link #ORIGINAL ORIGINAL} are always dropped
1642 * and so the resulting lookup mode will never have this access capability.
1643 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
1644 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
1645 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
1646 * is dropped then the resulting lookup has no access. If {@code UNCONDITIONAL}
1647 * is dropped then the resulting lookup has no access.
1648 *
1649 * @apiNote
1650 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1651 * delegate non-public access within the package of the lookup class without
1652 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1653 * A lookup with {@code MODULE} but not
1654 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1655 * the module of the lookup class without conferring package access.
1656 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1657 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1658 * to public classes accessible to both the module of the lookup class
1659 * and the module of the previous lookup class.
1660 *
1661 * @param modeToDrop the lookup mode to drop
1662 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1663 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1664 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
1665 * @see MethodHandles#privateLookupIn
1666 * @since 9
1667 */
1668 public Lookup dropLookupMode(int modeToDrop) {
1669 int oldModes = lookupModes();
1670 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1671 switch (modeToDrop) {
1672 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1673 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1674 case PACKAGE: newModes &= ~(PRIVATE); break;
1675 case PROTECTED:
1676 case PRIVATE:
1677 case UNCONDITIONAL: break;
1678 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1679 }
1680 if (newModes == oldModes) return this; // return self if no change
1681 return newLookup(lookupClass(), previousLookupClass(), newModes);
1682 }
1683
1684 /**
1685 * Defines a class to the same class loader and in the same runtime package and
1686 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1687 * {@linkplain #lookupClass() lookup class}.
1688 *
1689 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1690 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1691 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1692 * that the lookup object was created by a caller in the runtime package (or derived
1693 * from a lookup originally created by suitably privileged code to a target class in
1694 * the runtime package). </p>
1695 *
1696 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1697 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1698 * same package as the lookup class. </p>
1699 *
1700 * <p> This method does not run the class initializer.
1701 * The class initializer may run at a later time, as detailed in section 12.4 of
1702 * the <em>The Java Language Specification</em>. </p>
1703 *
1704 * <p> If there is a security manager and this lookup does not have {@linkplain
1705 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1706 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1707 *
1708 * @param bytes the class bytes
1709 * @return the {@code Class} object for the class
1710 * @throws IllegalArgumentException the bytes are for a class in a different package
1711 * to the lookup class
1712 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1713 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1714 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
1715 * @throws SecurityException if a security manager is present and it
1716 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1717 * @throws NullPointerException if {@code bytes} is {@code null}
1718 * @since 9
1719 * @spec JPMS
1720 * @see Lookup#privateLookupIn
1721 * @see Lookup#dropLookupMode
1722 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1723 */
1724 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1725 ensureDefineClassPermission();
1726 if ((lookupModes() & PACKAGE) == 0)
1727 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1728 return makeClassDefiner(bytes.clone()).defineClass(false);
1729 }
1730
1731 private void ensureDefineClassPermission() {
1732 if (allowedModes == TRUSTED) return;
1733
1734 if (!hasFullPrivilegeAccess()) {
1735 SecurityManager sm = System.getSecurityManager();
1736 if (sm != null)
1737 sm.checkPermission(new RuntimePermission("defineClass"));
1738 }
1739 }
1740
1741 /**
1742 * Creates a <em>hidden</em> class or interface from {@code bytes},
1743 * returning a {@code Lookup} on the newly created class or interface.
1744 *
1745 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1746 * which either defines {@code C} directly or delegates to another class loader.
1747 * A class loader defines {@code C} directly by invoking
1748 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1749 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1750 * to derive {@code C} from a purported representation in {@code class} file format.
1751 * In situations where use of a class loader is undesirable, a class or interface
1752 * {@code C} can be created by this method instead. This method is capable of
1753 * defining {@code C}, and thereby creating it, without invoking
1754 * {@code ClassLoader::defineClass}.
1755 * Instead, this method defines {@code C} as if by arranging for
1756 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1757 * from a purported representation in {@code class} file format
1758 * using the following rules:
1759 *
1760 * <ol>
1761 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1762 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1763 * This level of access is needed to create {@code C} in the module
1764 * of the lookup class of this {@code Lookup}.</li>
1765 *
1766 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1767 * structure of a supported major and minor version. The major and minor version
1768 * may differ from the {@code class} file version of the lookup class of this
1769 * {@code Lookup}.</li>
1770 *
1771 * <li> The value of {@code this_class} must be a valid index in the
1772 * {@code constant_pool} table, and the entry at that index must be a valid
1773 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1774 * encoded in internal form that is specified by this structure. {@code N} must
1775 * denote a class or interface in the same package as the lookup class.</li>
1776 *
1777 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1778 * where {@code <suffix>} is an unqualified name that is guaranteed to be unique
1779 * during this execution of the JVM.
1780 *
1781 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1782 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1783 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1784 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1785 * refers to the new {@code CONSTANT_Utf8_info} structure.
1786 *
1787 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1788 *
1789 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1790 * purported representation {@code newBytes} as if by the rules of JVMS 5.3.5,
1791 * with the following adjustments:
1792 * <ul>
1793 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1794 * that includes a single {@code "."} character, even though this is not a valid
1795 * binary class or interface name in internal form.</li>
1796 *
1797 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1798 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1799 *
1800 * <li> {@code C} is considered to have the same runtime package and
1801 * {@linkplain java.security.ProtectionDomain protection domain}
1802 * as the lookup class of this {@code Lookup}.
1803 *
1804 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1805 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1806 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C},
1807 * {@link Class#getName()} returns the string {@code GN + "/" + <suffix>}, even though
1808 * this is not a valid binary class or interface name.</li>
1809 * </ul>
1810 * </li>
1811 * </ol>
1812 *
1813 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1814 * Linkage occurs as specified in JVMS 5.4.3, with the following adjustments:
1815 * <ul>
1816 * <li> During verification, whenever it is necessary to load the class named
1817 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
1818 * made of any class loader.</li>
1819 *
1820 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
1821 * by {@code this_class}, the symbolic reference is considered to be resolved to
1822 * {@code C} and resolution always succeeds immediately.</li>
1823 * </ul>
1824 *
1825 * <p> If the {@code initialize} parameter is {@code true},
1826 * then {@code C} is initialized by the Java Virtual Machine.
1827 *
1828 * <p>The newly created class or interface {@code C} is <em>hidden</em>, in the sense that
1829 * no other class or interface can refer to {@code C} via a constant pool entry.
1830 * That is, a hidden class or interface cannot be named as a supertype, a field type,
1831 * a method parameter type, or a method return type by any other class.
1832 * This is because a hidden class or interface does not have a binary name, so
1833 * there is no internal form available to record in any class's constant pool.
1834 * (Given the {@code Lookup} object returned this method, its lookup class
1835 * is a {@code Class} object for which {@link Class#getName()} returns a string
1836 * that is not a binary name.)
1837 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
1838 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
1839 * is not {@linkplain java.lang.instrument.Instrumentation#isModifiableClass(Class)
1840 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
1841 * JVM Tool Interface</a>.
1842 *
1843 * <p> If {@code options} has the {@link ClassOption#NESTMATE NESTMATE} option, then
1844 * the newly created class or interface {@code C} is a member of a nest. The nest
1845 * to which {@code C} belongs is not based on any {@code NestHost} attribute in
1846 * the {@code ClassFile} structure from which {@code C} was derived.
1847 * Instead, the following rules determine the nest host of {@code C}:
1848 * <ul>
1849 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
1850 * been determined, then {@code H} be the nest host of the lookup class.</li>
1851 * <li>Otherwise, it is determined using the algorithm in JVMS 5.4.4, yielding {@code H}.</li>
1852 * <li>The nest host of {@code C} is determined to be {@code H}, the nest host of the lookup class.</li>
1853 * </ul>
1854 *
1855 * <p> If {@code options} has {@link ClassOption#WEAK WEAK} option, then
1856 * the newly created class or interface is <em>not strongly referenced</em> from
1857 * its defining class loader. Therefore, it may be unloaded while
1858 * its defining class loader is strongly reachable.
1859 *
1860 * <p> A hidden class or interface may be serializable, but this requires a custom
1861 * serialization mechanism in order to ensure that instances are properly serialized
1862 * and deserialized. The default serialization mechanism supports only classes and
1863 * interfaces that are discoverable by their class name.
1864 *
1865 * @param bytes the bytes that make up the class data,
1866 * in the format of a valid {@code class} file as defined by
1867 * <cite>The Java Virtual Machine Specification</cite>.
1868 * @param initialize if {@code true} the class will be initialized.
1869 * @param options {@linkplain ClassOption class options}
1870 * @return the {@code Lookup} object on the hidden class
1871 *
1872 * @throws IllegalAccessException if this {@code Lookup} does not have
1873 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
1874 * @throws SecurityException if a security manager is present and it
1875 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1876 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1877 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
1878 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
1879 * {@bytes} denotes a class in a different package than the lookup class
1880 * @throws IncompatibleClassChangeError if the class or interface named as
1881 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
1882 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
1883 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
1884 * {@code C} is {@code C} itself
1885 * @throws VerifyError if the newly created class cannot be verified
1886 * @throws LinkageError if the newly created class cannot be linked for any other reason
1887 * @throws NullPointerException if any parameter is {@code null}
1888 *
1889 * @since 15
1890 * @see Class#isHiddenClass()
1891 * @jvms 4.2.1 Binary Class and Interface Names
1892 * @jvms 4.2.2 Unqualified Names
1893 * @jvms 5.4.3.1 Class and Interface Resolution
1894 * @jvms 5.4.4 Access Control
1895 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
1896 * @jvms 5.4 Linking
1897 * @jvms 5.5 Initialization
1898 */
1899 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
1900 throws IllegalAccessException
1901 {
1902 Objects.requireNonNull(bytes);
1903 Objects.requireNonNull(options);
1904
1905 ensureDefineClassPermission();
1906 if (!hasFullPrivilegeAccess()) {
1907 throw new IllegalAccessException(this + " does not have full privilege access");
1908 }
1909
1910 Set<ClassOption> opts = options.length > 0 ? Set.of(options) : Set.of();
1911 return makeHiddenClassDefiner(bytes.clone(), opts).defineClassAsLookup(initialize);
1912 }
1913
1914 /**
1915 * Creates a <em>hidden</em> class or interface from {@code bytes} with {@code classData},
1916 * returning a {@code Lookup} on the newly created class or interface.
1917 *
1918 * <p> This method is equivalent to calling
1919 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
1920 * as if the hidden class has a private static final unnamed field
1921 * pre-initialized with the given {@code classData}.
1922 * The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData} method
1923 * can be used to retrieve the {@code classData}.
1924 *
1925 * @param bytes the class bytes
1926 * @param classData pre-initialized class data
1927 * @param initialize if {@code true} the class will be initialized.
1928 * @param options {@linkplain ClassOption class options}
1929 * @return the {@code Lookup} object on the hidden class
1930 *
1931 * @throws IllegalAccessException if this {@code Lookup} does not have
1932 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
1933 * @throws SecurityException if a security manager is present and it
1934 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1935 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1936 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
1937 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
1938 * {@bytes} denotes a class in a different package than the lookup class
1939 * @throws IncompatibleClassChangeError if the class or interface named as the direct superclass of {@code C}
1940 * is in fact an interface, or if any of the classes or interfaces named as direct superinterfaces of {@code C}
1941 * are not in fact interfaces
1942 * @throws ClassCircularityError if any of the superclasses or superinterfaces of {@code C} is {@code C} itself
1943 * @throws VerifyError if the newly created class cannot be verified
1944 * @throws LinkageError if the newly created class cannot be linked for any other reason
1945 * @throws NullPointerException if any parameter is {@code null}
1946 *
1947 * @since 15
1948 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1949 * @see Class#isHiddenClass()
1950 */
1951 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
1952 throws IllegalAccessException
1953 {
1954 Objects.requireNonNull(bytes);
1955 Objects.requireNonNull(classData);
1956 Objects.requireNonNull(options);
1957
1958 ensureDefineClassPermission();
1959 if (!hasFullPrivilegeAccess()) {
1960 throw new IllegalAccessException(this + " does not have full privilege access");
1961 }
1962
1963 Set<ClassOption> opts = options.length > 0 ? Set.of(options) : Set.of();
1964 return makeHiddenClassDefiner(bytes.clone(), opts).defineClassAsLookup(initialize, classData);
1965 }
1966
1967 private ClassDefiner makeClassDefiner(byte[] bytes) {
1968 return new ClassDefiner(this, bytes, Set.of(), 0);
1969 }
1970
1971 /**
1972 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
1973 * from the given bytes and options.
1974 *
1975 * @param bytes class bytes
1976 * @param options class options
1977 * @return ClassDefiner that defines a hidden class of the given bytes and options
1978 */
1979 ClassDefiner makeHiddenClassDefiner(byte[] bytes, Set<ClassOption> options) {
1980 return new ClassDefiner(this, bytes, options, HIDDEN_CLASS);
1981 }
1982
1983 /**
1984 * This method is only called by MethodHandleImpl.BindCaller.makeInjectedInvoker.
1985 *
1986 * @param name the name of the class and the name in the class bytes is ignored.
1987 * @param bytes class bytes
1988 * @return ClassDefiner that defines a hidden class of the given bytes
1989 */
1990 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, int flags) {
1991 return new ClassDefiner(this, name, bytes, HIDDEN_CLASS|flags);
1992 }
1993
1994 static class ClassDefiner {
1995 private final Lookup lookup;
1996 private final String name;
1997 private final byte[] bytes;
1998 private final int classFlags;
1999
2000 // caller should make a defensive copy of the arguments if needed
2001 // before calling this constructor
2002 private ClassDefiner(Lookup lookup, byte[] bytes, Set<ClassOption> options, int flags) {
2003 this.lookup = lookup;
2004 this.bytes = bytes;
2005 this.classFlags = flags | ClassOption.optionsToFlag(options);
2006 this.name = className(bytes);
2007
2008 int index = name.lastIndexOf('.');
2009 String pn = (index == -1) ? "" : name.substring(0, index);
2010 if (!pn.equals(lookup.lookupClass().getPackageName())) {
2011 throw newIllegalArgumentException(name + " not in same package as lookup class: " +
2012 lookup.lookupClass().getName());
2013 }
2014 }
2015
2016 // skip package name check
2017 private ClassDefiner(Lookup lookup, String name, byte[] bytes, int flags) {
2018 this.lookup = lookup;
2019 this.bytes = bytes;
2020 this.classFlags = flags;
2021 this.name = name;
2022 }
2023
2024 String className() {
2025 return name;
2026 }
2027
2028 Class<?> defineClass(boolean initialize) {
2029 return defineClass(initialize, null);
2030 }
2031
2032 Lookup defineClassAsLookup(boolean initialize) {
2033 Class<?> c = defineClass(initialize, null);
2034 return new Lookup(c, null, FULL_POWER_MODES);
2035 }
2036
2037 /**
2038 * Defines the class of the given bytes and the given classData.
2039 * If {@code initialize} parameter is true, then the class will be initialized.
2040 *
2041 * @param initialize true if the class to be initialized
2042 * @param classData classData or null
2043 * @return the class
2044 *
2045 * @throws LinkageError linkage error
2046 */
2047 Class<?> defineClass(boolean initialize, Object classData) {
2048 Class<?> lookupClass = lookup.lookupClass();
2049 ClassLoader loader = lookupClass.getClassLoader();
2050 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2051 Class<?> c = JLA.defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2052 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2053 return c;
2054 }
2055
2056 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2057 Class<?> c = defineClass(initialize, classData);
2058 return new Lookup(c, null, FULL_POWER_MODES);
2059 }
2060
2061 private boolean isNestmate() {
2062 return (classFlags & NESTMATE_CLASS) != 0;
2063 }
2064
2065 private static String className(byte[] bytes) {
2066 try {
2067 ClassReader reader = new ClassReader(bytes);
2068 if ((reader.getAccess() & Opcodes.ACC_MODULE) != 0) {
2069 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2070 }
2071 String name = reader.getClassName();
2072 return name.replace('/', '.');
2073 } catch (IllegalArgumentException e) {
2074 throw e;
2075 } catch (RuntimeException e) {
2076 // ASM exceptions are poorly specified
2077 ClassFormatError cfe = new ClassFormatError();
2078 cfe.initCause(e);
2079 throw cfe;
2080 }
2081 }
2082 }
2083
2084 private ProtectionDomain lookupClassProtectionDomain() {
2085 ProtectionDomain pd = cachedProtectionDomain;
2086 if (pd == null) {
2087 cachedProtectionDomain = pd = JLA.protectionDomain(lookupClass);
2088 }
2089 return pd;
2090 }
2091
2092 // cached protection domain
2093 private volatile ProtectionDomain cachedProtectionDomain;
2094
2095 // Make sure outer class is initialized first.
2096 static { IMPL_NAMES.getClass(); }
2097
2098 /** Package-private version of lookup which is trusted. */
2099 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2100
2101 /** Version of lookup which is trusted minimally.
2102 * It can only be used to create method handles to publicly accessible
2103 * members in packages that are exported unconditionally.
2104 */
2105 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2106
2107 static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
2108
2109 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2110 String name = lookupClass.getName();
2111 if (name.startsWith("java.lang.invoke."))
2112 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2113 }
2114
2115 /**
2116 * Displays the name of the class from which lookups are to be made.
2117 * followed with "/" and the name of the {@linkplain #previousLookupClass()
2118 * previous lookup class} if present.
2119 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2120 * If there are restrictions on the access permitted to this lookup,
2121 * this is indicated by adding a suffix to the class name, consisting
2122 * of a slash and a keyword. The keyword represents the strongest
2123 * allowed access, and is chosen as follows:
2124 * <ul>
2125 * <li>If no access is allowed, the suffix is "/noaccess".
2126 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2127 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2128 * <li>If only public and module access are allowed, the suffix is "/module".
2129 * <li>If public and package access are allowed, the suffix is "/package".
2130 * <li>If public, package, and private access are allowed, the suffix is "/private".
2131 * </ul>
2132 * If none of the above cases apply, it is the case that full access
2133 * (public, module, package, private, and protected) is allowed.
2134 * In this case, no suffix is added.
2135 * This is true only of an object obtained originally from
2136 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2137 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2138 * always have restricted access, and will display a suffix.
2139 * <p>
2140 * (It may seem strange that protected access should be
2141 * stronger than private access. Viewed independently from
2142 * package access, protected access is the first to be lost,
2143 * because it requires a direct subclass relationship between
2144 * caller and callee.)
2145 * @see #in
2146 *
2147 * @revised 9
2148 * @spec JPMS
2149 */
2150 @Override
2151 public String toString() {
2152 String cname = lookupClass.getName();
2153 if (prevLookupClass != null)
2154 cname += "/" + prevLookupClass.getName();
2155 switch (allowedModes) {
2156 case 0: // no privileges
2157 return cname + "/noaccess";
2158 case UNCONDITIONAL:
2159 return cname + "/publicLookup";
2160 case PUBLIC:
2161 return cname + "/public";
2162 case PUBLIC|MODULE:
2163 return cname + "/module";
2164 case PUBLIC|PACKAGE:
2165 case PUBLIC|MODULE|PACKAGE:
2166 return cname + "/package";
2167 case PUBLIC|PACKAGE|PRIVATE:
2168 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2169 return cname + "/private";
2170 case FULL_POWER_MODES:
2171 case FULL_POWER_MODES & ~ORIGINAL:
2172 case FULL_POWER_MODES & ~(MODULE|ORIGINAL):
2173 return cname;
2174 case TRUSTED:
2175 return "/trusted"; // internal only; not exported
2176 default: // Should not happen, but it's a bitfield...
2177 cname = cname + "/" + Integer.toHexString(allowedModes);
2178 assert(false) : cname;
2179 return cname;
2180 }
2181 }
2182
2183 /**
2184 * Produces a method handle for a static method.
2185 * The type of the method handle will be that of the method.
2186 * (Since static methods do not take receivers, there is no
2187 * additional receiver argument inserted into the method handle type,
2188 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2189 * The method and all its argument types must be accessible to the lookup object.
2190 * <p>
2191 * The returned method handle will have
2192 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2193 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2194 * <p>
2195 * If the returned method handle is invoked, the method's class will
2196 * be initialized, if it has not already been initialized.
2197 * <p><b>Example:</b>
2198 * <blockquote><pre>{@code
2199 import static java.lang.invoke.MethodHandles.*;
2200 import static java.lang.invoke.MethodType.*;
2201 ...
2202 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2203 "asList", methodType(List.class, Object[].class));
2204 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2205 * }</pre></blockquote>
2206 * @param refc the class from which the method is accessed
2207 * @param name the name of the method
2208 * @param type the type of the method
2209 * @return the desired method handle
2210 * @throws NoSuchMethodException if the method does not exist
2211 * @throws IllegalAccessException if access checking fails,
2212 * or if the method is not {@code static},
2213 * or if the method's variable arity modifier bit
2214 * is set and {@code asVarargsCollector} fails
2215 * @throws SecurityException if a security manager is present and it
2216 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2217 * @throws NullPointerException if any argument is null
2218 */
2219 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2220 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2221 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2222 }
2223
2224 /**
2225 * Produces a method handle for a virtual method.
2226 * The type of the method handle will be that of the method,
2227 * with the receiver type (usually {@code refc}) prepended.
2228 * The method and all its argument types must be accessible to the lookup object.
2229 * <p>
2230 * When called, the handle will treat the first argument as a receiver
2231 * and, for non-private methods, dispatch on the receiver's type to determine which method
2232 * implementation to enter.
2233 * For private methods the named method in {@code refc} will be invoked on the receiver.
2234 * (The dispatching action is identical with that performed by an
2235 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2236 * <p>
2237 * The first argument will be of type {@code refc} if the lookup
2238 * class has full privileges to access the member. Otherwise
2239 * the member must be {@code protected} and the first argument
2240 * will be restricted in type to the lookup class.
2241 * <p>
2242 * The returned method handle will have
2243 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2244 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2245 * <p>
2246 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2247 * instructions and method handles produced by {@code findVirtual},
2248 * if the class is {@code MethodHandle} and the name string is
2249 * {@code invokeExact} or {@code invoke}, the resulting
2250 * method handle is equivalent to one produced by
2251 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2252 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2253 * with the same {@code type} argument.
2254 * <p>
2255 * If the class is {@code VarHandle} and the name string corresponds to
2256 * the name of a signature-polymorphic access mode method, the resulting
2257 * method handle is equivalent to one produced by
2258 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2259 * the access mode corresponding to the name string and with the same
2260 * {@code type} arguments.
2261 * <p>
2262 * <b>Example:</b>
2263 * <blockquote><pre>{@code
2264 import static java.lang.invoke.MethodHandles.*;
2265 import static java.lang.invoke.MethodType.*;
2266 ...
2267 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2268 "concat", methodType(String.class, String.class));
2269 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2270 "hashCode", methodType(int.class));
2271 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2272 "hashCode", methodType(int.class));
2273 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2274 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2275 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2276 // interface method:
2277 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2278 "subSequence", methodType(CharSequence.class, int.class, int.class));
2279 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2280 // constructor "internal method" must be accessed differently:
2281 MethodType MT_newString = methodType(void.class); //()V for new String()
2282 try { assertEquals("impossible", lookup()
2283 .findVirtual(String.class, "<init>", MT_newString));
2284 } catch (NoSuchMethodException ex) { } // OK
2285 MethodHandle MH_newString = publicLookup()
2286 .findConstructor(String.class, MT_newString);
2287 assertEquals("", (String) MH_newString.invokeExact());
2288 * }</pre></blockquote>
2289 *
2290 * @param refc the class or interface from which the method is accessed
2291 * @param name the name of the method
2292 * @param type the type of the method, with the receiver argument omitted
2293 * @return the desired method handle
2294 * @throws NoSuchMethodException if the method does not exist
2295 * @throws IllegalAccessException if access checking fails,
2296 * or if the method is {@code static},
2297 * or if the method's variable arity modifier bit
2298 * is set and {@code asVarargsCollector} fails
2299 * @throws SecurityException if a security manager is present and it
2300 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2301 * @throws NullPointerException if any argument is null
2302 */
2303 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2304 if (refc == MethodHandle.class) {
2305 MethodHandle mh = findVirtualForMH(name, type);
2306 if (mh != null) return mh;
2307 } else if (refc == VarHandle.class) {
2308 MethodHandle mh = findVirtualForVH(name, type);
2309 if (mh != null) return mh;
2310 }
2311 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2312 MemberName method = resolveOrFail(refKind, refc, name, type);
2313 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2314 }
2315 private MethodHandle findVirtualForMH(String name, MethodType type) {
2316 // these names require special lookups because of the implicit MethodType argument
2317 if ("invoke".equals(name))
2318 return invoker(type);
2319 if ("invokeExact".equals(name))
2320 return exactInvoker(type);
2321 assert(!MemberName.isMethodHandleInvokeName(name));
2322 return null;
2323 }
2324 private MethodHandle findVirtualForVH(String name, MethodType type) {
2325 try {
2326 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2327 } catch (IllegalArgumentException e) {
2328 return null;
2329 }
2330 }
2331
2332 /**
2333 * Produces a method handle which creates an object and initializes it, using
2334 * the constructor of the specified type.
2335 * The parameter types of the method handle will be those of the constructor,
2336 * while the return type will be a reference to the constructor's class.
2337 * The constructor and all its argument types must be accessible to the lookup object.
2338 * <p>
2339 * The requested type must have a return type of {@code void}.
2340 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2341 * <p>
2342 * The returned method handle will have
2343 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2344 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2345 * <p>
2346 * If the returned method handle is invoked, the constructor's class will
2347 * be initialized, if it has not already been initialized.
2348 * <p><b>Example:</b>
2349 * <blockquote><pre>{@code
2350 import static java.lang.invoke.MethodHandles.*;
2351 import static java.lang.invoke.MethodType.*;
2352 ...
2353 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2354 ArrayList.class, methodType(void.class, Collection.class));
2355 Collection orig = Arrays.asList("x", "y");
2356 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2357 assert(orig != copy);
2358 assertEquals(orig, copy);
2359 // a variable-arity constructor:
2360 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2361 ProcessBuilder.class, methodType(void.class, String[].class));
2362 ProcessBuilder pb = (ProcessBuilder)
2363 MH_newProcessBuilder.invoke("x", "y", "z");
2364 assertEquals("[x, y, z]", pb.command().toString());
2365 * }</pre></blockquote>
2366 * @param refc the class or interface from which the method is accessed
2367 * @param type the type of the method, with the receiver argument omitted, and a void return type
2368 * @return the desired method handle
2369 * @throws NoSuchMethodException if the constructor does not exist
2370 * @throws IllegalAccessException if access checking fails
2371 * or if the method's variable arity modifier bit
2372 * is set and {@code asVarargsCollector} fails
2373 * @throws SecurityException if a security manager is present and it
2374 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2375 * @throws NullPointerException if any argument is null
2376 */
2377 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2378 if (refc.isArray()) {
2379 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2380 }
2381 String name = "<init>";
2382 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2383 return getDirectConstructor(refc, ctor);
2384 }
2385
2386 /**
2387 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2388 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2389 * Such a resolution, as specified in JVMS 5.4.3.1 section, attempts to locate and load the class,
2390 * and then determines whether the class is accessible to this lookup object.
2391 * <p>
2392 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2393 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2394 *
2395 * @param targetName the fully qualified name of the class to be looked up.
2396 * @return the requested class.
2397 * @throws SecurityException if a security manager is present and it
2398 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2399 * @throws LinkageError if the linkage fails
2400 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2401 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2402 * modes.
2403 * @since 9
2404 * @jvms 5.4.3.1 Class and Interface Resolution
2405 */
2406 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2407 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2408 return accessClass(targetClass);
2409 }
2410
2411 /**
2412 * Determines if a class can be accessed from the lookup context defined by
2413 * this {@code Lookup} object. The static initializer of the class is not run.
2414 * <p>
2415 * If the {@code targetClass} is in the same module as the lookup class,
2416 * the lookup class is {@code LC} in module {@code M1} and
2417 * the previous lookup class is in module {@code M0} or
2418 * {@code null} if not present,
2419 * {@code targetClass} is accessible if and only if one of the following is true:
2420 * <ul>
2421 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2422 * {@code LC} or other class in the same nest of {@code LC}.</li>
2423 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2424 * in the same runtime package of {@code LC}.</li>
2425 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2426 * a public type in {@code M1}.</li>
2427 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2428 * a public type in a package exported by {@code M1} to at least {@code M0}
2429 * if the previous lookup class is present; otherwise, {@code targetClass}
2430 * is a public type in a package exported by {@code M1} unconditionally.</li>
2431 * </ul>
2432 *
2433 * <p>
2434 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2435 * can access public types in all modules when the type is in a package
2436 * that is exported unconditionally.
2437 * <p>
2438 * Otherwise, the target class is in a different module from {@code lookupClass},
2439 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2440 * is inaccessible.
2441 * <p>
2442 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2443 * {@code M1} is the module containing {@code lookupClass} and
2444 * {@code M2} is the module containing {@code targetClass},
2445 * then {@code targetClass} is accessible if and only if
2446 * <ul>
2447 * <li>{@code M1} reads {@code M2}, and
2448 * <li>{@code targetClass} is public and in a package exported by
2449 * {@code M2} at least to {@code M1}.
2450 * </ul>
2451 * <p>
2452 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2453 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2454 * containing the previous lookup class, then {@code targetClass} is accessible
2455 * if and only if one of the following is true:
2456 * <ul>
2457 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2458 * {@linkplain Module#reads reads} {@code M0} and the type is
2459 * in a package that is exported to at least {@code M1}.
2460 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2461 * {@linkplain Module#reads reads} {@code M1} and the type is
2462 * in a package that is exported to at least {@code M0}.
2463 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2464 * and {@code M1} reads {@code M2} and the type is in a package
2465 * that is exported to at least both {@code M0} and {@code M2}.
2466 * </ul>
2467 * <p>
2468 * Otherwise, {@code targetClass} is not accessible.
2469 *
2470 * @param targetClass the class to be access-checked
2471 * @return the class that has been access-checked
2472 * @throws IllegalAccessException if the class is not accessible from the lookup class
2473 * and previous lookup class, if present, using the allowed access modes.
2474 * @throws SecurityException if a security manager is present and it
2475 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2476 * @since 9
2477 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2478 */
2479 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2480 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2481 throw new MemberName(targetClass).makeAccessException("access violation", this);
2482 }
2483 checkSecurityManager(targetClass, null);
2484 return targetClass;
2485 }
2486
2487 /**
2488 * Produces an early-bound method handle for a virtual method.
2489 * It will bypass checks for overriding methods on the receiver,
2490 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2491 * instruction from within the explicitly specified {@code specialCaller}.
2492 * The type of the method handle will be that of the method,
2493 * with a suitably restricted receiver type prepended.
2494 * (The receiver type will be {@code specialCaller} or a subtype.)
2495 * The method and all its argument types must be accessible
2496 * to the lookup object.
2497 * <p>
2498 * Before method resolution,
2499 * if the explicitly specified caller class is not identical with the
2500 * lookup class, or if this lookup object does not have
2501 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2502 * privileges, the access fails.
2503 * <p>
2504 * The returned method handle will have
2505 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2506 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2507 * <p style="font-size:smaller;">
2508 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2509 * even though the {@code invokespecial} instruction can refer to them
2510 * in special circumstances. Use {@link #findConstructor findConstructor}
2511 * to access instance initialization methods in a safe manner.)</em>
2512 * <p><b>Example:</b>
2513 * <blockquote><pre>{@code
2514 import static java.lang.invoke.MethodHandles.*;
2515 import static java.lang.invoke.MethodType.*;
2516 ...
2517 static class Listie extends ArrayList {
2518 public String toString() { return "[wee Listie]"; }
2519 static Lookup lookup() { return MethodHandles.lookup(); }
2520 }
2521 ...
2522 // no access to constructor via invokeSpecial:
2523 MethodHandle MH_newListie = Listie.lookup()
2524 .findConstructor(Listie.class, methodType(void.class));
2525 Listie l = (Listie) MH_newListie.invokeExact();
2526 try { assertEquals("impossible", Listie.lookup().findSpecial(
2527 Listie.class, "<init>", methodType(void.class), Listie.class));
2528 } catch (NoSuchMethodException ex) { } // OK
2529 // access to super and self methods via invokeSpecial:
2530 MethodHandle MH_super = Listie.lookup().findSpecial(
2531 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2532 MethodHandle MH_this = Listie.lookup().findSpecial(
2533 Listie.class, "toString" , methodType(String.class), Listie.class);
2534 MethodHandle MH_duper = Listie.lookup().findSpecial(
2535 Object.class, "toString" , methodType(String.class), Listie.class);
2536 assertEquals("[]", (String) MH_super.invokeExact(l));
2537 assertEquals(""+l, (String) MH_this.invokeExact(l));
2538 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2539 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2540 String.class, "toString", methodType(String.class), Listie.class));
2541 } catch (IllegalAccessException ex) { } // OK
2542 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2543 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2544 * }</pre></blockquote>
2545 *
2546 * @param refc the class or interface from which the method is accessed
2547 * @param name the name of the method (which must not be "<init>")
2548 * @param type the type of the method, with the receiver argument omitted
2549 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2550 * @return the desired method handle
2551 * @throws NoSuchMethodException if the method does not exist
2552 * @throws IllegalAccessException if access checking fails,
2553 * or if the method is {@code static},
2554 * or if the method's variable arity modifier bit
2555 * is set and {@code asVarargsCollector} fails
2556 * @throws SecurityException if a security manager is present and it
2557 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2558 * @throws NullPointerException if any argument is null
2559 */
2560 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2561 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2562 checkSpecialCaller(specialCaller, refc);
2563 Lookup specialLookup = this.in(specialCaller);
2564 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2565 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
2566 }
2567
2568 /**
2569 * Produces a method handle giving read access to a non-static field.
2570 * The type of the method handle will have a return type of the field's
2571 * value type.
2572 * The method handle's single argument will be the instance containing
2573 * the field.
2574 * Access checking is performed immediately on behalf of the lookup class.
2575 * @param refc the class or interface from which the method is accessed
2576 * @param name the field's name
2577 * @param type the field's type
2578 * @return a method handle which can load values from the field
2579 * @throws NoSuchFieldException if the field does not exist
2580 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2581 * @throws SecurityException if a security manager is present and it
2582 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2583 * @throws NullPointerException if any argument is null
2584 * @see #findVarHandle(Class, String, Class)
2585 */
2586 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2587 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2588 return getDirectField(REF_getField, refc, field);
2589 }
2590
2591 /**
2592 * Produces a method handle giving write access to a non-static field.
2593 * The type of the method handle will have a void return type.
2594 * The method handle will take two arguments, the instance containing
2595 * the field, and the value to be stored.
2596 * The second argument will be of the field's value type.
2597 * Access checking is performed immediately on behalf of the lookup class.
2598 * @param refc the class or interface from which the method is accessed
2599 * @param name the field's name
2600 * @param type the field's type
2601 * @return a method handle which can store values into the field
2602 * @throws NoSuchFieldException if the field does not exist
2603 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2604 * or {@code final}
2605 * @throws SecurityException if a security manager is present and it
2606 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2607 * @throws NullPointerException if any argument is null
2608 * @see #findVarHandle(Class, String, Class)
2609 */
2610 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2611 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2612 return getDirectField(REF_putField, refc, field);
2613 }
2614
2615 /**
2616 * Produces a VarHandle giving access to a non-static field {@code name}
2617 * of type {@code type} declared in a class of type {@code recv}.
2618 * The VarHandle's variable type is {@code type} and it has one
2619 * coordinate type, {@code recv}.
2620 * <p>
2621 * Access checking is performed immediately on behalf of the lookup
2622 * class.
2623 * <p>
2624 * Certain access modes of the returned VarHandle are unsupported under
2625 * the following conditions:
2626 * <ul>
2627 * <li>if the field is declared {@code final}, then the write, atomic
2628 * update, numeric atomic update, and bitwise atomic update access
2629 * modes are unsupported.
2630 * <li>if the field type is anything other than {@code byte},
2631 * {@code short}, {@code char}, {@code int}, {@code long},
2632 * {@code float}, or {@code double} then numeric atomic update
2633 * access modes are unsupported.
2634 * <li>if the field type is anything other than {@code boolean},
2635 * {@code byte}, {@code short}, {@code char}, {@code int} or
2636 * {@code long} then bitwise atomic update access modes are
2637 * unsupported.
2638 * </ul>
2639 * <p>
2640 * If the field is declared {@code volatile} then the returned VarHandle
2641 * will override access to the field (effectively ignore the
2642 * {@code volatile} declaration) in accordance to its specified
2643 * access modes.
2644 * <p>
2645 * If the field type is {@code float} or {@code double} then numeric
2646 * and atomic update access modes compare values using their bitwise
2647 * representation (see {@link Float#floatToRawIntBits} and
2648 * {@link Double#doubleToRawLongBits}, respectively).
2649 * @apiNote
2650 * Bitwise comparison of {@code float} values or {@code double} values,
2651 * as performed by the numeric and atomic update access modes, differ
2652 * from the primitive {@code ==} operator and the {@link Float#equals}
2653 * and {@link Double#equals} methods, specifically with respect to
2654 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2655 * Care should be taken when performing a compare and set or a compare
2656 * and exchange operation with such values since the operation may
2657 * unexpectedly fail.
2658 * There are many possible NaN values that are considered to be
2659 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2660 * provided by Java can distinguish between them. Operation failure can
2661 * occur if the expected or witness value is a NaN value and it is
2662 * transformed (perhaps in a platform specific manner) into another NaN
2663 * value, and thus has a different bitwise representation (see
2664 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2665 * details).
2666 * The values {@code -0.0} and {@code +0.0} have different bitwise
2667 * representations but are considered equal when using the primitive
2668 * {@code ==} operator. Operation failure can occur if, for example, a
2669 * numeric algorithm computes an expected value to be say {@code -0.0}
2670 * and previously computed the witness value to be say {@code +0.0}.
2671 * @param recv the receiver class, of type {@code R}, that declares the
2672 * non-static field
2673 * @param name the field's name
2674 * @param type the field's type, of type {@code T}
2675 * @return a VarHandle giving access to non-static fields.
2676 * @throws NoSuchFieldException if the field does not exist
2677 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2678 * @throws SecurityException if a security manager is present and it
2679 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2680 * @throws NullPointerException if any argument is null
2681 * @since 9
2682 */
2683 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2684 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
2685 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
2686 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
2687 }
2688
2689 /**
2690 * Produces a method handle giving read access to a static field.
2691 * The type of the method handle will have a return type of the field's
2692 * value type.
2693 * The method handle will take no arguments.
2694 * Access checking is performed immediately on behalf of the lookup class.
2695 * <p>
2696 * If the returned method handle is invoked, the field's class will
2697 * be initialized, if it has not already been initialized.
2698 * @param refc the class or interface from which the method is accessed
2699 * @param name the field's name
2700 * @param type the field's type
2701 * @return a method handle which can load values from the field
2702 * @throws NoSuchFieldException if the field does not exist
2703 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2704 * @throws SecurityException if a security manager is present and it
2705 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2706 * @throws NullPointerException if any argument is null
2707 */
2708 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2709 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
2710 return getDirectField(REF_getStatic, refc, field);
2711 }
2712
2713 /**
2714 * Produces a method handle giving write access to a static field.
2715 * The type of the method handle will have a void return type.
2716 * The method handle will take a single
2717 * argument, of the field's value type, the value to be stored.
2718 * Access checking is performed immediately on behalf of the lookup class.
2719 * <p>
2720 * If the returned method handle is invoked, the field's class will
2721 * be initialized, if it has not already been initialized.
2722 * @param refc the class or interface from which the method is accessed
2723 * @param name the field's name
2724 * @param type the field's type
2725 * @return a method handle which can store values into the field
2726 * @throws NoSuchFieldException if the field does not exist
2727 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2728 * or is {@code final}
2729 * @throws SecurityException if a security manager is present and it
2730 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2731 * @throws NullPointerException if any argument is null
2732 */
2733 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2734 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
2735 return getDirectField(REF_putStatic, refc, field);
2736 }
2737
2738 /**
2739 * Produces a VarHandle giving access to a static field {@code name} of
2740 * type {@code type} declared in a class of type {@code decl}.
2741 * The VarHandle's variable type is {@code type} and it has no
2742 * coordinate types.
2743 * <p>
2744 * Access checking is performed immediately on behalf of the lookup
2745 * class.
2746 * <p>
2747 * If the returned VarHandle is operated on, the declaring class will be
2748 * initialized, if it has not already been initialized.
2749 * <p>
2750 * Certain access modes of the returned VarHandle are unsupported under
2751 * the following conditions:
2752 * <ul>
2753 * <li>if the field is declared {@code final}, then the write, atomic
2754 * update, numeric atomic update, and bitwise atomic update access
2755 * modes are unsupported.
2756 * <li>if the field type is anything other than {@code byte},
2757 * {@code short}, {@code char}, {@code int}, {@code long},
2758 * {@code float}, or {@code double}, then numeric atomic update
2759 * access modes are unsupported.
2760 * <li>if the field type is anything other than {@code boolean},
2761 * {@code byte}, {@code short}, {@code char}, {@code int} or
2762 * {@code long} then bitwise atomic update access modes are
2763 * unsupported.
2764 * </ul>
2765 * <p>
2766 * If the field is declared {@code volatile} then the returned VarHandle
2767 * will override access to the field (effectively ignore the
2768 * {@code volatile} declaration) in accordance to its specified
2769 * access modes.
2770 * <p>
2771 * If the field type is {@code float} or {@code double} then numeric
2772 * and atomic update access modes compare values using their bitwise
2773 * representation (see {@link Float#floatToRawIntBits} and
2774 * {@link Double#doubleToRawLongBits}, respectively).
2775 * @apiNote
2776 * Bitwise comparison of {@code float} values or {@code double} values,
2777 * as performed by the numeric and atomic update access modes, differ
2778 * from the primitive {@code ==} operator and the {@link Float#equals}
2779 * and {@link Double#equals} methods, specifically with respect to
2780 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2781 * Care should be taken when performing a compare and set or a compare
2782 * and exchange operation with such values since the operation may
2783 * unexpectedly fail.
2784 * There are many possible NaN values that are considered to be
2785 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2786 * provided by Java can distinguish between them. Operation failure can
2787 * occur if the expected or witness value is a NaN value and it is
2788 * transformed (perhaps in a platform specific manner) into another NaN
2789 * value, and thus has a different bitwise representation (see
2790 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2791 * details).
2792 * The values {@code -0.0} and {@code +0.0} have different bitwise
2793 * representations but are considered equal when using the primitive
2794 * {@code ==} operator. Operation failure can occur if, for example, a
2795 * numeric algorithm computes an expected value to be say {@code -0.0}
2796 * and previously computed the witness value to be say {@code +0.0}.
2797 * @param decl the class that declares the static field
2798 * @param name the field's name
2799 * @param type the field's type, of type {@code T}
2800 * @return a VarHandle giving access to a static field
2801 * @throws NoSuchFieldException if the field does not exist
2802 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2803 * @throws SecurityException if a security manager is present and it
2804 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2805 * @throws NullPointerException if any argument is null
2806 * @since 9
2807 */
2808 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2809 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
2810 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
2811 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
2812 }
2813
2814 /**
2815 * Produces an early-bound method handle for a non-static method.
2816 * The receiver must have a supertype {@code defc} in which a method
2817 * of the given name and type is accessible to the lookup class.
2818 * The method and all its argument types must be accessible to the lookup object.
2819 * The type of the method handle will be that of the method,
2820 * without any insertion of an additional receiver parameter.
2821 * The given receiver will be bound into the method handle,
2822 * so that every call to the method handle will invoke the
2823 * requested method on the given receiver.
2824 * <p>
2825 * The returned method handle will have
2826 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2827 * the method's variable arity modifier bit ({@code 0x0080}) is set
2828 * <em>and</em> the trailing array argument is not the only argument.
2829 * (If the trailing array argument is the only argument,
2830 * the given receiver value will be bound to it.)
2831 * <p>
2832 * This is almost equivalent to the following code, with some differences noted below:
2833 * <blockquote><pre>{@code
2834 import static java.lang.invoke.MethodHandles.*;
2835 import static java.lang.invoke.MethodType.*;
2836 ...
2837 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
2838 MethodHandle mh1 = mh0.bindTo(receiver);
2839 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
2840 return mh1;
2841 * }</pre></blockquote>
2842 * where {@code defc} is either {@code receiver.getClass()} or a super
2843 * type of that class, in which the requested method is accessible
2844 * to the lookup class.
2845 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
2846 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
2847 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
2848 * the receiver is restricted by {@code findVirtual} to the lookup class.)
2849 * @param receiver the object from which the method is accessed
2850 * @param name the name of the method
2851 * @param type the type of the method, with the receiver argument omitted
2852 * @return the desired method handle
2853 * @throws NoSuchMethodException if the method does not exist
2854 * @throws IllegalAccessException if access checking fails
2855 * or if the method's variable arity modifier bit
2856 * is set and {@code asVarargsCollector} fails
2857 * @throws SecurityException if a security manager is present and it
2858 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2859 * @throws NullPointerException if any argument is null
2860 * @see MethodHandle#bindTo
2861 * @see #findVirtual
2862 */
2863 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2864 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2865 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2866 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
2867 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2868 throw new IllegalAccessException("The restricted defining class " +
2869 mh.type().leadingReferenceParameter().getName() +
2870 " is not assignable from receiver class " +
2871 receiver.getClass().getName());
2872 }
2873 return mh.bindArgumentL(0, receiver).setVarargs(method);
2874 }
2875
2876 /**
2877 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2878 * to <i>m</i>, if the lookup class has permission.
2879 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2880 * If <i>m</i> is virtual, overriding is respected on every call.
2881 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2882 * The type of the method handle will be that of the method,
2883 * with the receiver type prepended (but only if it is non-static).
2884 * If the method's {@code accessible} flag is not set,
2885 * access checking is performed immediately on behalf of the lookup class.
2886 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2887 * <p>
2888 * The returned method handle will have
2889 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2890 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2891 * <p>
2892 * If <i>m</i> is static, and
2893 * if the returned method handle is invoked, the method's class will
2894 * be initialized, if it has not already been initialized.
2895 * @param m the reflected method
2896 * @return a method handle which can invoke the reflected method
2897 * @throws IllegalAccessException if access checking fails
2898 * or if the method's variable arity modifier bit
2899 * is set and {@code asVarargsCollector} fails
2900 * @throws NullPointerException if the argument is null
2901 */
2902 public MethodHandle unreflect(Method m) throws IllegalAccessException {
2903 if (m.getDeclaringClass() == MethodHandle.class) {
2904 MethodHandle mh = unreflectForMH(m);
2905 if (mh != null) return mh;
2906 }
2907 if (m.getDeclaringClass() == VarHandle.class) {
2908 MethodHandle mh = unreflectForVH(m);
2909 if (mh != null) return mh;
2910 }
2911 MemberName method = new MemberName(m);
2912 byte refKind = method.getReferenceKind();
2913 if (refKind == REF_invokeSpecial)
2914 refKind = REF_invokeVirtual;
2915 assert(method.isMethod());
2916 @SuppressWarnings("deprecation")
2917 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
2918 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
2919 }
2920 private MethodHandle unreflectForMH(Method m) {
2921 // these names require special lookups because they throw UnsupportedOperationException
2922 if (MemberName.isMethodHandleInvokeName(m.getName()))
2923 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
2924 return null;
2925 }
2926 private MethodHandle unreflectForVH(Method m) {
2927 // these names require special lookups because they throw UnsupportedOperationException
2928 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
2929 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
2930 return null;
2931 }
2932
2933 /**
2934 * Produces a method handle for a reflected method.
2935 * It will bypass checks for overriding methods on the receiver,
2936 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2937 * instruction from within the explicitly specified {@code specialCaller}.
2938 * The type of the method handle will be that of the method,
2939 * with a suitably restricted receiver type prepended.
2940 * (The receiver type will be {@code specialCaller} or a subtype.)
2941 * If the method's {@code accessible} flag is not set,
2942 * access checking is performed immediately on behalf of the lookup class,
2943 * as if {@code invokespecial} instruction were being linked.
2944 * <p>
2945 * Before method resolution,
2946 * if the explicitly specified caller class is not identical with the
2947 * lookup class, or if this lookup object does not have
2948 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2949 * privileges, the access fails.
2950 * <p>
2951 * The returned method handle will have
2952 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2953 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2954 * @param m the reflected method
2955 * @param specialCaller the class nominally calling the method
2956 * @return a method handle which can invoke the reflected method
2957 * @throws IllegalAccessException if access checking fails,
2958 * or if the method is {@code static},
2959 * or if the method's variable arity modifier bit
2960 * is set and {@code asVarargsCollector} fails
2961 * @throws NullPointerException if any argument is null
2962 */
2963 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
2964 checkSpecialCaller(specialCaller, m.getDeclaringClass());
2965 Lookup specialLookup = this.in(specialCaller);
2966 MemberName method = new MemberName(m, true);
2967 assert(method.isMethod());
2968 // ignore m.isAccessible: this is a new kind of access
2969 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
2970 }
2971
2972 /**
2973 * Produces a method handle for a reflected constructor.
2974 * The type of the method handle will be that of the constructor,
2975 * with the return type changed to the declaring class.
2976 * The method handle will perform a {@code newInstance} operation,
2977 * creating a new instance of the constructor's class on the
2978 * arguments passed to the method handle.
2979 * <p>
2980 * If the constructor's {@code accessible} flag is not set,
2981 * access checking is performed immediately on behalf of the lookup class.
2982 * <p>
2983 * The returned method handle will have
2984 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2985 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2986 * <p>
2987 * If the returned method handle is invoked, the constructor's class will
2988 * be initialized, if it has not already been initialized.
2989 * @param c the reflected constructor
2990 * @return a method handle which can invoke the reflected constructor
2991 * @throws IllegalAccessException if access checking fails
2992 * or if the method's variable arity modifier bit
2993 * is set and {@code asVarargsCollector} fails
2994 * @throws NullPointerException if the argument is null
2995 */
2996 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
2997 MemberName ctor = new MemberName(c);
2998 assert(ctor.isConstructor());
2999 @SuppressWarnings("deprecation")
3000 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3001 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3002 }
3003
3004 /**
3005 * Produces a method handle giving read access to a reflected field.
3006 * The type of the method handle will have a return type of the field's
3007 * value type.
3008 * If the field is {@code static}, the method handle will take no arguments.
3009 * Otherwise, its single argument will be the instance containing
3010 * the field.
3011 * If the {@code Field} object's {@code accessible} flag is not set,
3012 * access checking is performed immediately on behalf of the lookup class.
3013 * <p>
3014 * If the field is static, and
3015 * if the returned method handle is invoked, the field's class will
3016 * be initialized, if it has not already been initialized.
3017 * @param f the reflected field
3018 * @return a method handle which can load values from the reflected field
3019 * @throws IllegalAccessException if access checking fails
3020 * @throws NullPointerException if the argument is null
3021 */
3022 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3023 return unreflectField(f, false);
3024 }
3025
3026 /**
3027 * Produces a method handle giving write access to a reflected field.
3028 * The type of the method handle will have a void return type.
3029 * If the field is {@code static}, the method handle will take a single
3030 * argument, of the field's value type, the value to be stored.
3031 * Otherwise, the two arguments will be the instance containing
3032 * the field, and the value to be stored.
3033 * If the {@code Field} object's {@code accessible} flag is not set,
3034 * access checking is performed immediately on behalf of the lookup class.
3035 * <p>
3036 * If the field is {@code final}, write access will not be
3037 * allowed and access checking will fail, except under certain
3038 * narrow circumstances documented for {@link Field#set Field.set}.
3039 * A method handle is returned only if a corresponding call to
3040 * the {@code Field} object's {@code set} method could return
3041 * normally. In particular, fields which are both {@code static}
3042 * and {@code final} may never be set.
3043 * <p>
3044 * If the field is {@code static}, and
3045 * if the returned method handle is invoked, the field's class will
3046 * be initialized, if it has not already been initialized.
3047 * @param f the reflected field
3048 * @return a method handle which can store values into the reflected field
3049 * @throws IllegalAccessException if access checking fails,
3050 * or if the field is {@code final} and write access
3051 * is not enabled on the {@code Field} object
3052 * @throws NullPointerException if the argument is null
3053 */
3054 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3055 return unreflectField(f, true);
3056 }
3057
3058 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3059 MemberName field = new MemberName(f, isSetter);
3060 if (isSetter && field.isFinal()) {
3061 if (field.isStatic()) {
3062 throw field.makeAccessException("static final field has no write access", this);
3063 } else if (field.getDeclaringClass().isHiddenClass()){
3064 throw field.makeAccessException("final field in a hidden class has no write access", this);
3065 }
3066 }
3067 assert(isSetter
3068 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3069 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3070 @SuppressWarnings("deprecation")
3071 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3072 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3073 }
3074
3075 /**
3076 * Produces a VarHandle giving access to a reflected field {@code f}
3077 * of type {@code T} declared in a class of type {@code R}.
3078 * The VarHandle's variable type is {@code T}.
3079 * If the field is non-static the VarHandle has one coordinate type,
3080 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3081 * coordinate types.
3082 * <p>
3083 * Access checking is performed immediately on behalf of the lookup
3084 * class, regardless of the value of the field's {@code accessible}
3085 * flag.
3086 * <p>
3087 * If the field is static, and if the returned VarHandle is operated
3088 * on, the field's declaring class will be initialized, if it has not
3089 * already been initialized.
3090 * <p>
3091 * Certain access modes of the returned VarHandle are unsupported under
3092 * the following conditions:
3093 * <ul>
3094 * <li>if the field is declared {@code final}, then the write, atomic
3095 * update, numeric atomic update, and bitwise atomic update access
3096 * modes are unsupported.
3097 * <li>if the field type is anything other than {@code byte},
3098 * {@code short}, {@code char}, {@code int}, {@code long},
3099 * {@code float}, or {@code double} then numeric atomic update
3100 * access modes are unsupported.
3101 * <li>if the field type is anything other than {@code boolean},
3102 * {@code byte}, {@code short}, {@code char}, {@code int} or
3103 * {@code long} then bitwise atomic update access modes are
3104 * unsupported.
3105 * </ul>
3106 * <p>
3107 * If the field is declared {@code volatile} then the returned VarHandle
3108 * will override access to the field (effectively ignore the
3109 * {@code volatile} declaration) in accordance to its specified
3110 * access modes.
3111 * <p>
3112 * If the field type is {@code float} or {@code double} then numeric
3113 * and atomic update access modes compare values using their bitwise
3114 * representation (see {@link Float#floatToRawIntBits} and
3115 * {@link Double#doubleToRawLongBits}, respectively).
3116 * @apiNote
3117 * Bitwise comparison of {@code float} values or {@code double} values,
3118 * as performed by the numeric and atomic update access modes, differ
3119 * from the primitive {@code ==} operator and the {@link Float#equals}
3120 * and {@link Double#equals} methods, specifically with respect to
3121 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3122 * Care should be taken when performing a compare and set or a compare
3123 * and exchange operation with such values since the operation may
3124 * unexpectedly fail.
3125 * There are many possible NaN values that are considered to be
3126 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3127 * provided by Java can distinguish between them. Operation failure can
3128 * occur if the expected or witness value is a NaN value and it is
3129 * transformed (perhaps in a platform specific manner) into another NaN
3130 * value, and thus has a different bitwise representation (see
3131 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3132 * details).
3133 * The values {@code -0.0} and {@code +0.0} have different bitwise
3134 * representations but are considered equal when using the primitive
3135 * {@code ==} operator. Operation failure can occur if, for example, a
3136 * numeric algorithm computes an expected value to be say {@code -0.0}
3137 * and previously computed the witness value to be say {@code +0.0}.
3138 * @param f the reflected field, with a field of type {@code T}, and
3139 * a declaring class of type {@code R}
3140 * @return a VarHandle giving access to non-static fields or a static
3141 * field
3142 * @throws IllegalAccessException if access checking fails
3143 * @throws NullPointerException if the argument is null
3144 * @since 9
3145 */
3146 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3147 MemberName getField = new MemberName(f, false);
3148 MemberName putField = new MemberName(f, true);
3149 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3150 f.getDeclaringClass(), getField, putField);
3151 }
3152
3153 /**
3154 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3155 * created by this lookup object or a similar one.
3156 * Security and access checks are performed to ensure that this lookup object
3157 * is capable of reproducing the target method handle.
3158 * This means that the cracking may fail if target is a direct method handle
3159 * but was created by an unrelated lookup object.
3160 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3161 * and was created by a lookup object for a different class.
3162 * @param target a direct method handle to crack into symbolic reference components
3163 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3164 * @throws SecurityException if a security manager is present and it
3165 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3166 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3167 * @throws NullPointerException if the target is {@code null}
3168 * @see MethodHandleInfo
3169 * @since 1.8
3170 */
3171 public MethodHandleInfo revealDirect(MethodHandle target) {
3172 MemberName member = target.internalMemberName();
3173 if (member == null || (!member.isResolved() &&
3174 !member.isMethodHandleInvoke() &&
3175 !member.isVarHandleMethodInvoke()))
3176 throw newIllegalArgumentException("not a direct method handle");
3177 Class<?> defc = member.getDeclaringClass();
3178 byte refKind = member.getReferenceKind();
3179 assert(MethodHandleNatives.refKindIsValid(refKind));
3180 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3181 // Devirtualized method invocation is usually formally virtual.
3182 // To avoid creating extra MemberName objects for this common case,
3183 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3184 refKind = REF_invokeVirtual;
3185 if (refKind == REF_invokeVirtual && defc.isInterface())
3186 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3187 refKind = REF_invokeInterface;
3188 // Check SM permissions and member access before cracking.
3189 try {
3190 checkAccess(refKind, defc, member);
3191 checkSecurityManager(defc, member);
3192 } catch (IllegalAccessException ex) {
3193 throw new IllegalArgumentException(ex);
3194 }
3195 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3196 Class<?> callerClass = target.internalCallerClass();
3197 if (!hasFullPrivilegeAccess() || callerClass != lookupClass())
3198 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3199 }
3200 // Produce the handle to the results.
3201 return new InfoFromMemberName(this, member, refKind);
3202 }
3203
3204 /// Helper methods, all package-private.
3205
3206 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3207 checkSymbolicClass(refc); // do this before attempting to resolve
3208 Objects.requireNonNull(name);
3209 Objects.requireNonNull(type);
3210 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
3211 NoSuchFieldException.class);
3212 }
3213
3214 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3215 checkSymbolicClass(refc); // do this before attempting to resolve
3216 Objects.requireNonNull(name);
3217 Objects.requireNonNull(type);
3218 checkMethodName(refKind, name); // NPE check on name
3219 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
3220 NoSuchMethodException.class);
3221 }
3222
3223 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3224 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3225 Objects.requireNonNull(member.getName());
3226 Objects.requireNonNull(member.getType());
3227 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
3228 ReflectiveOperationException.class);
3229 }
3230
3231 MemberName resolveOrNull(byte refKind, MemberName member) {
3232 // do this before attempting to resolve
3233 if (!isClassAccessible(member.getDeclaringClass())) {
3234 return null;
3235 }
3236 Objects.requireNonNull(member.getName());
3237 Objects.requireNonNull(member.getType());
3238 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
3239 }
3240
3241 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3242 if (!isClassAccessible(refc)) {
3243 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3244 }
3245 }
3246
3247 boolean isClassAccessible(Class<?> refc) {
3248 Objects.requireNonNull(refc);
3249 Class<?> caller = lookupClassOrNull();
3250 return caller == null || VerifyAccess.isClassAccessible(refc, caller, prevLookupClass, allowedModes);
3251 }
3252
3253 /** Check name for an illegal leading "<" character. */
3254 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3255 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3256 throw new NoSuchMethodException("illegal method name: "+name);
3257 }
3258
3259
3260 /**
3261 * Find my trustable caller class if m is a caller sensitive method.
3262 * If this lookup object has full privilege access, then the caller class is the lookupClass.
3263 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3264 */
3265 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3266 if (MethodHandleNatives.isCallerSensitive(m) && !hasFullPrivilegeAccess()) {
3267 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3268 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3269 }
3270 return this;
3271 }
3272
3273 /**
3274 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3275 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3276 *
3277 * @deprecated This method was originally designed to test {@code PRIVATE} access
3278 * that implies full privilege access but {@code MODULE} access has since become
3279 * independent of {@code PRIVATE} access. It is recommended to call
3280 * {@link #hasFullPrivilegeAccess()} instead.
3281 * @since 9
3282 */
3283 @Deprecated(since="14")
3284 public boolean hasPrivateAccess() {
3285 return hasFullPrivilegeAccess();
3286 }
3287
3288 /**
3289 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3290 * i.e. {@code PRIVATE} and {@code MODULE} access.
3291 * A {@code Lookup} object must have full privilege access in order to
3292 * access all members that are allowed to the {@linkplain #lookupClass() lookup class}.
3293 *
3294 * @return {@code true} if this lookup has full privilege access.
3295 * @since 14
3296 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3297 */
3298 public boolean hasFullPrivilegeAccess() {
3299 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3300 }
3301
3302 /**
3303 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3304 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3305 * If this lookup object has full privilege access, then the caller class is the lookupClass.
3306 */
3307 void checkSecurityManager(Class<?> refc, MemberName m) {
3308 if (allowedModes == TRUSTED) return;
3309
3310 SecurityManager smgr = System.getSecurityManager();
3311 if (smgr == null) return;
3312
3313 // Step 1:
3314 boolean fullPowerLookup = hasFullPrivilegeAccess();
3315 if (!fullPowerLookup ||
3316 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3317 ReflectUtil.checkPackageAccess(refc);
3318 }
3319
3320 if (m == null) { // findClass or accessClass
3321 // Step 2b:
3322 if (!fullPowerLookup) {
3323 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3324 }
3325 return;
3326 }
3327
3328 // Step 2a:
3329 if (m.isPublic()) return;
3330 if (!fullPowerLookup) {
3331 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3332 }
3333
3334 // Step 3:
3335 Class<?> defc = m.getDeclaringClass();
3336 if (!fullPowerLookup && defc != refc) {
3337 ReflectUtil.checkPackageAccess(defc);
3338 }
3339 }
3340
3341 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3342 boolean wantStatic = (refKind == REF_invokeStatic);
3343 String message;
3344 if (m.isConstructor())
3345 message = "expected a method, not a constructor";
3346 else if (!m.isMethod())
3347 message = "expected a method";
3348 else if (wantStatic != m.isStatic())
3349 message = wantStatic ? "expected a static method" : "expected a non-static method";
3350 else
3351 { checkAccess(refKind, refc, m); return; }
3352 throw m.makeAccessException(message, this);
3353 }
3354
3355 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3356 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3357 String message;
3358 if (wantStatic != m.isStatic())
3359 message = wantStatic ? "expected a static field" : "expected a non-static field";
3360 else
3361 { checkAccess(refKind, refc, m); return; }
3362 throw m.makeAccessException(message, this);
3363 }
3364
3365 /** Check public/protected/private bits on the symbolic reference class and its member. */
3366 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3367 assert(m.referenceKindIsConsistentWith(refKind) &&
3368 MethodHandleNatives.refKindIsValid(refKind) &&
3369 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3370 int allowedModes = this.allowedModes;
3371 if (allowedModes == TRUSTED) return;
3372 int mods = m.getModifiers();
3373 if (Modifier.isProtected(mods) &&
3374 refKind == REF_invokeVirtual &&
3375 m.getDeclaringClass() == Object.class &&
3376 m.getName().equals("clone") &&
3377 refc.isArray()) {
3378 // The JVM does this hack also.
3379 // (See ClassVerifier::verify_invoke_instructions
3380 // and LinkResolver::check_method_accessability.)
3381 // Because the JVM does not allow separate methods on array types,
3382 // there is no separate method for int[].clone.
3383 // All arrays simply inherit Object.clone.
3384 // But for access checking logic, we make Object.clone
3385 // (normally protected) appear to be public.
3386 // Later on, when the DirectMethodHandle is created,
3387 // its leading argument will be restricted to the
3388 // requested array type.
3389 // N.B. The return type is not adjusted, because
3390 // that is *not* the bytecode behavior.
3391 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3392 }
3393 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3394 // cannot "new" a protected ctor in a different package
3395 mods ^= Modifier.PROTECTED;
3396 }
3397 if (Modifier.isFinal(mods) &&
3398 MethodHandleNatives.refKindIsSetter(refKind))
3399 throw m.makeAccessException("unexpected set of a final field", this);
3400 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3401 if ((requestedModes & allowedModes) != 0) {
3402 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3403 mods, lookupClass(), previousLookupClass(), allowedModes))
3404 return;
3405 } else {
3406 // Protected members can also be checked as if they were package-private.
3407 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3408 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3409 return;
3410 }
3411 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3412 }
3413
3414 String accessFailedMessage(Class<?> refc, MemberName m) {
3415 Class<?> defc = m.getDeclaringClass();
3416 int mods = m.getModifiers();
3417 // check the class first:
3418 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3419 (defc == refc ||
3420 Modifier.isPublic(refc.getModifiers())));
3421 if (!classOK && (allowedModes & PACKAGE) != 0) {
3422 // ignore previous lookup class to check if default package access
3423 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3424 (defc == refc ||
3425 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3426 }
3427 if (!classOK)
3428 return "class is not public";
3429 if (Modifier.isPublic(mods))
3430 return "access to public member failed"; // (how?, module not readable?)
3431 if (Modifier.isPrivate(mods))
3432 return "member is private";
3433 if (Modifier.isProtected(mods))
3434 return "member is protected";
3435 return "member is private to package";
3436 }
3437
3438 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3439 int allowedModes = this.allowedModes;
3440 if (allowedModes == TRUSTED) return;
3441 if ((lookupModes() & PRIVATE) == 0
3442 || (specialCaller != lookupClass()
3443 // ensure non-abstract methods in superinterfaces can be special-invoked
3444 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3445 throw new MemberName(specialCaller).
3446 makeAccessException("no private access for invokespecial", this);
3447 }
3448
3449 private boolean restrictProtectedReceiver(MemberName method) {
3450 // The accessing class only has the right to use a protected member
3451 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3452 if (!method.isProtected() || method.isStatic()
3453 || allowedModes == TRUSTED
3454 || method.getDeclaringClass() == lookupClass()
3455 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3456 return false;
3457 return true;
3458 }
3459 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3460 assert(!method.isStatic());
3461 // receiver type of mh is too wide; narrow to caller
3462 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3463 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3464 }
3465 MethodType rawType = mh.type();
3466 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3467 MethodType narrowType = rawType.changeParameterType(0, caller);
3468 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3469 assert(mh.viewAsTypeChecks(narrowType, true));
3470 return mh.copyWith(narrowType, mh.form);
3471 }
3472
3473 /** Check access and get the requested method. */
3474 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3475 final boolean doRestrict = true;
3476 final boolean checkSecurity = true;
3477 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3478 }
3479 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3480 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3481 final boolean doRestrict = false;
3482 final boolean checkSecurity = true;
3483 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
3484 }
3485 /** Check access and get the requested method, eliding security manager checks. */
3486 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3487 final boolean doRestrict = true;
3488 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3489 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3490 }
3491 /** Common code for all methods; do not call directly except from immediately above. */
3492 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3493 boolean checkSecurity,
3494 boolean doRestrict,
3495 Lookup boundCaller) throws IllegalAccessException {
3496 checkMethod(refKind, refc, method);
3497 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3498 if (checkSecurity)
3499 checkSecurityManager(refc, method);
3500 assert(!method.isMethodHandleInvoke());
3501
3502 if (refKind == REF_invokeSpecial &&
3503 refc != lookupClass() &&
3504 !refc.isInterface() &&
3505 refc != lookupClass().getSuperclass() &&
3506 refc.isAssignableFrom(lookupClass())) {
3507 assert(!method.getName().equals("<init>")); // not this code path
3508
3509 // Per JVMS 6.5, desc. of invokespecial instruction:
3510 // If the method is in a superclass of the LC,
3511 // and if our original search was above LC.super,
3512 // repeat the search (symbolic lookup) from LC.super
3513 // and continue with the direct superclass of that class,
3514 // and so forth, until a match is found or no further superclasses exist.
3515 // FIXME: MemberName.resolve should handle this instead.
3516 Class<?> refcAsSuper = lookupClass();
3517 MemberName m2;
3518 do {
3519 refcAsSuper = refcAsSuper.getSuperclass();
3520 m2 = new MemberName(refcAsSuper,
3521 method.getName(),
3522 method.getMethodType(),
3523 REF_invokeSpecial);
3524 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
3525 } while (m2 == null && // no method is found yet
3526 refc != refcAsSuper); // search up to refc
3527 if (m2 == null) throw new InternalError(method.toString());
3528 method = m2;
3529 refc = refcAsSuper;
3530 // redo basic checks
3531 checkMethod(refKind, refc, method);
3532 }
3533 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3534 MethodHandle mh = dmh;
3535 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3536 if ((doRestrict && refKind == REF_invokeSpecial) ||
3537 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
3538 mh = restrictReceiver(method, dmh, lookupClass());
3539 }
3540 mh = maybeBindCaller(method, mh, boundCaller);
3541 mh = mh.setVarargs(method);
3542 return mh;
3543 }
3544 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
3545 throws IllegalAccessException {
3546 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3547 return mh;
3548
3549 // boundCaller must have full privilege access.
3550 // It should have been checked by findBoundCallerLookup. Safe to check this again.
3551 if (!boundCaller.hasFullPrivilegeAccess())
3552 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3553
3554 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
3555 // Note: caller will apply varargs after this step happens.
3556 return cbmh;
3557 }
3558
3559 /** Check access and get the requested field. */
3560 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3561 final boolean checkSecurity = true;
3562 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3563 }
3564 /** Check access and get the requested field, eliding security manager checks. */
3565 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3566 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3567 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3568 }
3569 /** Common code for all fields; do not call directly except from immediately above. */
3570 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
3571 boolean checkSecurity) throws IllegalAccessException {
3572 checkField(refKind, refc, field);
3573 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3574 if (checkSecurity)
3575 checkSecurityManager(refc, field);
3576 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3577 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3578 restrictProtectedReceiver(field));
3579 if (doRestrict)
3580 return restrictReceiver(field, dmh, lookupClass());
3581 return dmh;
3582 }
3583 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3584 Class<?> refc, MemberName getField, MemberName putField)
3585 throws IllegalAccessException {
3586 final boolean checkSecurity = true;
3587 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3588 }
3589 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
3590 Class<?> refc, MemberName getField, MemberName putField)
3591 throws IllegalAccessException {
3592 final boolean checkSecurity = false;
3593 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3594 }
3595 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3596 Class<?> refc, MemberName getField, MemberName putField,
3597 boolean checkSecurity) throws IllegalAccessException {
3598 assert getField.isStatic() == putField.isStatic();
3599 assert getField.isGetter() && putField.isSetter();
3600 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3601 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3602
3603 checkField(getRefKind, refc, getField);
3604 if (checkSecurity)
3605 checkSecurityManager(refc, getField);
3606
3607 if (!putField.isFinal()) {
3608 // A VarHandle does not support updates to final fields, any
3609 // such VarHandle to a final field will be read-only and
3610 // therefore the following write-based accessibility checks are
3611 // only required for non-final fields
3612 checkField(putRefKind, refc, putField);
3613 if (checkSecurity)
3614 checkSecurityManager(refc, putField);
3615 }
3616
3617 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3618 restrictProtectedReceiver(getField));
3619 if (doRestrict) {
3620 assert !getField.isStatic();
3621 // receiver type of VarHandle is too wide; narrow to caller
3622 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3623 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3624 }
3625 refc = lookupClass();
3626 }
3627 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(),
3628 this.allowedModes == TRUSTED && !getField.getDeclaringClass().isHiddenClass());
3629 }
3630 /** Check access and get the requested constructor. */
3631 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3632 final boolean checkSecurity = true;
3633 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3634 }
3635 /** Check access and get the requested constructor, eliding security manager checks. */
3636 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3637 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3638 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3639 }
3640 /** Common code for all constructors; do not call directly except from immediately above. */
3641 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
3642 boolean checkSecurity) throws IllegalAccessException {
3643 assert(ctor.isConstructor());
3644 checkAccess(REF_newInvokeSpecial, refc, ctor);
3645 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3646 if (checkSecurity)
3647 checkSecurityManager(refc, ctor);
3648 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3649 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3650 }
3651
3652 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3653 */
3654 /*non-public*/
3655 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
3656 throws ReflectiveOperationException {
3657 if (!(type instanceof Class || type instanceof MethodType))
3658 throw new InternalError("unresolved MemberName");
3659 MemberName member = new MemberName(refKind, defc, name, type);
3660 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3661 if (mh != null) {
3662 checkSymbolicClass(defc);
3663 return mh;
3664 }
3665 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3666 // Treat MethodHandle.invoke and invokeExact specially.
3667 mh = findVirtualForMH(member.getName(), member.getMethodType());
3668 if (mh != null) {
3669 return mh;
3670 }
3671 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3672 // Treat signature-polymorphic methods on VarHandle specially.
3673 mh = findVirtualForVH(member.getName(), member.getMethodType());
3674 if (mh != null) {
3675 return mh;
3676 }
3677 }
3678 MemberName resolved = resolveOrFail(refKind, member);
3679 mh = getDirectMethodForConstant(refKind, defc, resolved);
3680 if (mh instanceof DirectMethodHandle
3681 && canBeCached(refKind, defc, resolved)) {
3682 MemberName key = mh.internalMemberName();
3683 if (key != null) {
3684 key = key.asNormalOriginal();
3685 }
3686 if (member.equals(key)) { // better safe than sorry
3687 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
3688 }
3689 }
3690 return mh;
3691 }
3692 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
3693 if (refKind == REF_invokeSpecial) {
3694 return false;
3695 }
3696 if (!Modifier.isPublic(defc.getModifiers()) ||
3697 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
3698 !member.isPublic() ||
3699 member.isCallerSensitive()) {
3700 return false;
3701 }
3702 ClassLoader loader = defc.getClassLoader();
3703 if (loader != null) {
3704 ClassLoader sysl = ClassLoader.getSystemClassLoader();
3705 boolean found = false;
3706 while (sysl != null) {
3707 if (loader == sysl) { found = true; break; }
3708 sysl = sysl.getParent();
3709 }
3710 if (!found) {
3711 return false;
3712 }
3713 }
3714 try {
3715 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
3716 new MemberName(refKind, defc, member.getName(), member.getType()));
3717 if (resolved2 == null) {
3718 return false;
3719 }
3720 checkSecurityManager(defc, resolved2);
3721 } catch (SecurityException ex) {
3722 return false;
3723 }
3724 return true;
3725 }
3726 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
3727 throws ReflectiveOperationException {
3728 if (MethodHandleNatives.refKindIsField(refKind)) {
3729 return getDirectFieldNoSecurityManager(refKind, defc, member);
3730 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
3731 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
3732 } else if (refKind == REF_newInvokeSpecial) {
3733 return getDirectConstructorNoSecurityManager(defc, member);
3734 }
3735 // oops
3736 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
3737 }
3738
3739 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
3740
3741 /**
3742 * The set of class options that specify whether a hidden class created by
3743 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
3744 * Lookup::defineHiddenMethod} method is dynamically added as
3745 * a new member to the nest of a lookup class and whether a hidden class
3746 * is weak such that it may be unloaded while its defining class loader
3747 * is <a href="../ref/package.html#reachability">strongly reachable</a>.
3748 *
3749 * @since 15
3750 */
3751 public enum ClassOption {
3752 /**
3753 * This class option specifies the hidden class be added to
3754 * {@linkplain Class#getNestHost nest} of a lookup class as
3755 * a nestmate.
3756 *
3757 * <p> A hidden nestmate class has access to the private members of all
3758 * classes and interfaces in the same nest.
3759 *
3760 * @see Class#getNestHost()
3761 */
3762 NESTMATE(NESTMATE_CLASS),
3763
3764 /**
3765 * This class option specifies the hidden class be weak so that
3766 * the class is not strongly referenced by its defining class loader.
3767 * A weak class may be unloaded while its defining class loader is
3768 * <a href="../ref/package.html#reachability">strongly reachable</a>.
3769 *
3770 * @jls 12.7 Unloading of Classes and Interfaces
3771 */
3772 WEAK(WEAK_CLASS);
3773
3774 /* the flag value is used by VM at define class time */
3775 private final int flag;
3776 ClassOption(int flag) {
3777 this.flag = flag;
3778 }
3779
3780 static int optionsToFlag(Set<ClassOption> options) {
3781 int flags = 0;
3782 for (ClassOption cp : options) {
3783 flags |= cp.flag;
3784 }
3785 return flags;
3786 }
3787 }
3788 }
3789
3790 /**
3791 * Produces a method handle constructing arrays of a desired type,
3792 * as if by the {@code anewarray} bytecode.
3793 * The return type of the method handle will be the array type.
3794 * The type of its sole argument will be {@code int}, which specifies the size of the array.
3795 *
3796 * <p> If the returned method handle is invoked with a negative
3797 * array size, a {@code NegativeArraySizeException} will be thrown.
3798 *
3799 * @param arrayClass an array type
3800 * @return a method handle which can create arrays of the given type
3801 * @throws NullPointerException if the argument is {@code null}
3802 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
3803 * @see java.lang.reflect.Array#newInstance(Class, int)
3804 * @jvms 6.5 {@code anewarray} Instruction
3805 * @since 9
3806 */
3807 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
3808 if (!arrayClass.isArray()) {
3809 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
3810 }
3811 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
3812 bindTo(arrayClass.getComponentType());
3813 return ani.asType(ani.type().changeReturnType(arrayClass));
3814 }
3815
3816 /**
3817 * Produces a method handle returning the length of an array,
3818 * as if by the {@code arraylength} bytecode.
3819 * The type of the method handle will have {@code int} as return type,
3820 * and its sole argument will be the array type.
3821 *
3822 * <p> If the returned method handle is invoked with a {@code null}
3823 * array reference, a {@code NullPointerException} will be thrown.
3824 *
3825 * @param arrayClass an array type
3826 * @return a method handle which can retrieve the length of an array of the given array type
3827 * @throws NullPointerException if the argument is {@code null}
3828 * @throws IllegalArgumentException if arrayClass is not an array type
3829 * @jvms 6.5 {@code arraylength} Instruction
3830 * @since 9
3831 */
3832 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
3833 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
3834 }
3835
3836 /**
3837 * Produces a method handle giving read access to elements of an array,
3838 * as if by the {@code aaload} bytecode.
3839 * The type of the method handle will have a return type of the array's
3840 * element type. Its first argument will be the array type,
3841 * and the second will be {@code int}.
3842 *
3843 * <p> When the returned method handle is invoked,
3844 * the array reference and array index are checked.
3845 * A {@code NullPointerException} will be thrown if the array reference
3846 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3847 * thrown if the index is negative or if it is greater than or equal to
3848 * the length of the array.
3849 *
3850 * @param arrayClass an array type
3851 * @return a method handle which can load values from the given array type
3852 * @throws NullPointerException if the argument is null
3853 * @throws IllegalArgumentException if arrayClass is not an array type
3854 * @jvms 6.5 {@code aaload} Instruction
3855 */
3856 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
3857 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
3858 }
3859
3860 /**
3861 * Produces a method handle giving write access to elements of an array,
3862 * as if by the {@code astore} bytecode.
3863 * The type of the method handle will have a void return type.
3864 * Its last argument will be the array's element type.
3865 * The first and second arguments will be the array type and int.
3866 *
3867 * <p> When the returned method handle is invoked,
3868 * the array reference and array index are checked.
3869 * A {@code NullPointerException} will be thrown if the array reference
3870 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3871 * thrown if the index is negative or if it is greater than or equal to
3872 * the length of the array.
3873 *
3874 * @param arrayClass the class of an array
3875 * @return a method handle which can store values into the array type
3876 * @throws NullPointerException if the argument is null
3877 * @throws IllegalArgumentException if arrayClass is not an array type
3878 * @jvms 6.5 {@code aastore} Instruction
3879 */
3880 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
3881 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
3882 }
3883
3884 /**
3885 * Produces a VarHandle giving access to elements of an array of type
3886 * {@code arrayClass}. The VarHandle's variable type is the component type
3887 * of {@code arrayClass} and the list of coordinate types is
3888 * {@code (arrayClass, int)}, where the {@code int} coordinate type
3889 * corresponds to an argument that is an index into an array.
3890 * <p>
3891 * Certain access modes of the returned VarHandle are unsupported under
3892 * the following conditions:
3893 * <ul>
3894 * <li>if the component type is anything other than {@code byte},
3895 * {@code short}, {@code char}, {@code int}, {@code long},
3896 * {@code float}, or {@code double} then numeric atomic update access
3897 * modes are unsupported.
3898 * <li>if the field type is anything other than {@code boolean},
3899 * {@code byte}, {@code short}, {@code char}, {@code int} or
3900 * {@code long} then bitwise atomic update access modes are
3901 * unsupported.
3902 * </ul>
3903 * <p>
3904 * If the component type is {@code float} or {@code double} then numeric
3905 * and atomic update access modes compare values using their bitwise
3906 * representation (see {@link Float#floatToRawIntBits} and
3907 * {@link Double#doubleToRawLongBits}, respectively).
3908 *
3909 * <p> When the returned {@code VarHandle} is invoked,
3910 * the array reference and array index are checked.
3911 * A {@code NullPointerException} will be thrown if the array reference
3912 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3913 * thrown if the index is negative or if it is greater than or equal to
3914 * the length of the array.
3915 *
3916 * @apiNote
3917 * Bitwise comparison of {@code float} values or {@code double} values,
3918 * as performed by the numeric and atomic update access modes, differ
3919 * from the primitive {@code ==} operator and the {@link Float#equals}
3920 * and {@link Double#equals} methods, specifically with respect to
3921 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3922 * Care should be taken when performing a compare and set or a compare
3923 * and exchange operation with such values since the operation may
3924 * unexpectedly fail.
3925 * There are many possible NaN values that are considered to be
3926 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3927 * provided by Java can distinguish between them. Operation failure can
3928 * occur if the expected or witness value is a NaN value and it is
3929 * transformed (perhaps in a platform specific manner) into another NaN
3930 * value, and thus has a different bitwise representation (see
3931 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3932 * details).
3933 * The values {@code -0.0} and {@code +0.0} have different bitwise
3934 * representations but are considered equal when using the primitive
3935 * {@code ==} operator. Operation failure can occur if, for example, a
3936 * numeric algorithm computes an expected value to be say {@code -0.0}
3937 * and previously computed the witness value to be say {@code +0.0}.
3938 * @param arrayClass the class of an array, of type {@code T[]}
3939 * @return a VarHandle giving access to elements of an array
3940 * @throws NullPointerException if the arrayClass is null
3941 * @throws IllegalArgumentException if arrayClass is not an array type
3942 * @since 9
3943 */
3944 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
3945 return VarHandles.makeArrayElementHandle(arrayClass);
3946 }
3947
3948 /**
3949 * Produces a VarHandle giving access to elements of a {@code byte[]} array
3950 * viewed as if it were a different primitive array type, such as
3951 * {@code int[]} or {@code long[]}.
3952 * The VarHandle's variable type is the component type of
3953 * {@code viewArrayClass} and the list of coordinate types is
3954 * {@code (byte[], int)}, where the {@code int} coordinate type
3955 * corresponds to an argument that is an index into a {@code byte[]} array.
3956 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
3957 * array, composing bytes to or from a value of the component type of
3958 * {@code viewArrayClass} according to the given endianness.
3959 * <p>
3960 * The supported component types (variables types) are {@code short},
3961 * {@code char}, {@code int}, {@code long}, {@code float} and
3962 * {@code double}.
3963 * <p>
3964 * Access of bytes at a given index will result in an
3965 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3966 * or greater than the {@code byte[]} array length minus the size (in bytes)
3967 * of {@code T}.
3968 * <p>
3969 * Access of bytes at an index may be aligned or misaligned for {@code T},
3970 * with respect to the underlying memory address, {@code A} say, associated
3971 * with the array and index.
3972 * If access is misaligned then access for anything other than the
3973 * {@code get} and {@code set} access modes will result in an
3974 * {@code IllegalStateException}. In such cases atomic access is only
3975 * guaranteed with respect to the largest power of two that divides the GCD
3976 * of {@code A} and the size (in bytes) of {@code T}.
3977 * If access is aligned then following access modes are supported and are
3978 * guaranteed to support atomic access:
3979 * <ul>
3980 * <li>read write access modes for all {@code T}, with the exception of
3981 * access modes {@code get} and {@code set} for {@code long} and
3982 * {@code double} on 32-bit platforms.
3983 * <li>atomic update access modes for {@code int}, {@code long},
3984 * {@code float} or {@code double}.
3985 * (Future major platform releases of the JDK may support additional
3986 * types for certain currently unsupported access modes.)
3987 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3988 * (Future major platform releases of the JDK may support additional
3989 * numeric types for certain currently unsupported access modes.)
3990 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3991 * (Future major platform releases of the JDK may support additional
3992 * numeric types for certain currently unsupported access modes.)
3993 * </ul>
3994 * <p>
3995 * Misaligned access, and therefore atomicity guarantees, may be determined
3996 * for {@code byte[]} arrays without operating on a specific array. Given
3997 * an {@code index}, {@code T} and it's corresponding boxed type,
3998 * {@code T_BOX}, misalignment may be determined as follows:
3999 * <pre>{@code
4000 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4001 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4002 * alignmentOffset(0, sizeOfT);
4003 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4004 * boolean isMisaligned = misalignedAtIndex != 0;
4005 * }</pre>
4006 * <p>
4007 * If the variable type is {@code float} or {@code double} then atomic
4008 * update access modes compare values using their bitwise representation
4009 * (see {@link Float#floatToRawIntBits} and
4010 * {@link Double#doubleToRawLongBits}, respectively).
4011 * @param viewArrayClass the view array class, with a component type of
4012 * type {@code T}
4013 * @param byteOrder the endianness of the view array elements, as
4014 * stored in the underlying {@code byte} array
4015 * @return a VarHandle giving access to elements of a {@code byte[]} array
4016 * viewed as if elements corresponding to the components type of the view
4017 * array class
4018 * @throws NullPointerException if viewArrayClass or byteOrder is null
4019 * @throws IllegalArgumentException if viewArrayClass is not an array type
4020 * @throws UnsupportedOperationException if the component type of
4021 * viewArrayClass is not supported as a variable type
4022 * @since 9
4023 */
4024 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4025 ByteOrder byteOrder) throws IllegalArgumentException {
4026 Objects.requireNonNull(byteOrder);
4027 return VarHandles.byteArrayViewHandle(viewArrayClass,
4028 byteOrder == ByteOrder.BIG_ENDIAN);
4029 }
4030
4031 /**
4032 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4033 * viewed as if it were an array of elements of a different primitive
4034 * component type to that of {@code byte}, such as {@code int[]} or
4035 * {@code long[]}.
4036 * The VarHandle's variable type is the component type of
4037 * {@code viewArrayClass} and the list of coordinate types is
4038 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4039 * corresponds to an argument that is an index into a {@code byte[]} array.
4040 * The returned VarHandle accesses bytes at an index in a
4041 * {@code ByteBuffer}, composing bytes to or from a value of the component
4042 * type of {@code viewArrayClass} according to the given endianness.
4043 * <p>
4044 * The supported component types (variables types) are {@code short},
4045 * {@code char}, {@code int}, {@code long}, {@code float} and
4046 * {@code double}.
4047 * <p>
4048 * Access will result in a {@code ReadOnlyBufferException} for anything
4049 * other than the read access modes if the {@code ByteBuffer} is read-only.
4050 * <p>
4051 * Access of bytes at a given index will result in an
4052 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4053 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4054 * {@code T}.
4055 * <p>
4056 * Access of bytes at an index may be aligned or misaligned for {@code T},
4057 * with respect to the underlying memory address, {@code A} say, associated
4058 * with the {@code ByteBuffer} and index.
4059 * If access is misaligned then access for anything other than the
4060 * {@code get} and {@code set} access modes will result in an
4061 * {@code IllegalStateException}. In such cases atomic access is only
4062 * guaranteed with respect to the largest power of two that divides the GCD
4063 * of {@code A} and the size (in bytes) of {@code T}.
4064 * If access is aligned then following access modes are supported and are
4065 * guaranteed to support atomic access:
4066 * <ul>
4067 * <li>read write access modes for all {@code T}, with the exception of
4068 * access modes {@code get} and {@code set} for {@code long} and
4069 * {@code double} on 32-bit platforms.
4070 * <li>atomic update access modes for {@code int}, {@code long},
4071 * {@code float} or {@code double}.
4072 * (Future major platform releases of the JDK may support additional
4073 * types for certain currently unsupported access modes.)
4074 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4075 * (Future major platform releases of the JDK may support additional
4076 * numeric types for certain currently unsupported access modes.)
4077 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4078 * (Future major platform releases of the JDK may support additional
4079 * numeric types for certain currently unsupported access modes.)
4080 * </ul>
4081 * <p>
4082 * Misaligned access, and therefore atomicity guarantees, may be determined
4083 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4084 * {@code index}, {@code T} and it's corresponding boxed type,
4085 * {@code T_BOX}, as follows:
4086 * <pre>{@code
4087 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4088 * ByteBuffer bb = ...
4089 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4090 * boolean isMisaligned = misalignedAtIndex != 0;
4091 * }</pre>
4092 * <p>
4093 * If the variable type is {@code float} or {@code double} then atomic
4094 * update access modes compare values using their bitwise representation
4095 * (see {@link Float#floatToRawIntBits} and
4096 * {@link Double#doubleToRawLongBits}, respectively).
4097 * @param viewArrayClass the view array class, with a component type of
4098 * type {@code T}
4099 * @param byteOrder the endianness of the view array elements, as
4100 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4101 * endianness of a {@code ByteBuffer})
4102 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4103 * viewed as if elements corresponding to the components type of the view
4104 * array class
4105 * @throws NullPointerException if viewArrayClass or byteOrder is null
4106 * @throws IllegalArgumentException if viewArrayClass is not an array type
4107 * @throws UnsupportedOperationException if the component type of
4108 * viewArrayClass is not supported as a variable type
4109 * @since 9
4110 */
4111 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4112 ByteOrder byteOrder) throws IllegalArgumentException {
4113 Objects.requireNonNull(byteOrder);
4114 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4115 byteOrder == ByteOrder.BIG_ENDIAN);
4116 }
4117
4118
4119 /// method handle invocation (reflective style)
4120
4121 /**
4122 * Produces a method handle which will invoke any method handle of the
4123 * given {@code type}, with a given number of trailing arguments replaced by
4124 * a single trailing {@code Object[]} array.
4125 * The resulting invoker will be a method handle with the following
4126 * arguments:
4127 * <ul>
4128 * <li>a single {@code MethodHandle} target
4129 * <li>zero or more leading values (counted by {@code leadingArgCount})
4130 * <li>an {@code Object[]} array containing trailing arguments
4131 * </ul>
4132 * <p>
4133 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4134 * the indicated {@code type}.
4135 * That is, if the target is exactly of the given {@code type}, it will behave
4136 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4137 * is used to convert the target to the required {@code type}.
4138 * <p>
4139 * The type of the returned invoker will not be the given {@code type}, but rather
4140 * will have all parameters except the first {@code leadingArgCount}
4141 * replaced by a single array of type {@code Object[]}, which will be
4142 * the final parameter.
4143 * <p>
4144 * Before invoking its target, the invoker will spread the final array, apply
4145 * reference casts as necessary, and unbox and widen primitive arguments.
4146 * If, when the invoker is called, the supplied array argument does
4147 * not have the correct number of elements, the invoker will throw
4148 * an {@link IllegalArgumentException} instead of invoking the target.
4149 * <p>
4150 * This method is equivalent to the following code (though it may be more efficient):
4151 * <blockquote><pre>{@code
4152 MethodHandle invoker = MethodHandles.invoker(type);
4153 int spreadArgCount = type.parameterCount() - leadingArgCount;
4154 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4155 return invoker;
4156 * }</pre></blockquote>
4157 * This method throws no reflective or security exceptions.
4158 * @param type the desired target type
4159 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4160 * @return a method handle suitable for invoking any method handle of the given type
4161 * @throws NullPointerException if {@code type} is null
4162 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4163 * the range from 0 to {@code type.parameterCount()} inclusive,
4164 * or if the resulting method handle's type would have
4165 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4166 */
4167 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4168 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4169 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4170 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4171 return type.invokers().spreadInvoker(leadingArgCount);
4172 }
4173
4174 /**
4175 * Produces a special <em>invoker method handle</em> which can be used to
4176 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4177 * The resulting invoker will have a type which is
4178 * exactly equal to the desired type, except that it will accept
4179 * an additional leading argument of type {@code MethodHandle}.
4180 * <p>
4181 * This method is equivalent to the following code (though it may be more efficient):
4182 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4183 *
4184 * <p style="font-size:smaller;">
4185 * <em>Discussion:</em>
4186 * Invoker method handles can be useful when working with variable method handles
4187 * of unknown types.
4188 * For example, to emulate an {@code invokeExact} call to a variable method
4189 * handle {@code M}, extract its type {@code T},
4190 * look up the invoker method {@code X} for {@code T},
4191 * and call the invoker method, as {@code X.invoke(T, A...)}.
4192 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4193 * is unknown.)
4194 * If spreading, collecting, or other argument transformations are required,
4195 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4196 * method handle values, as long as they are compatible with the type of {@code X}.
4197 * <p style="font-size:smaller;">
4198 * <em>(Note: The invoker method is not available via the Core Reflection API.
4199 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4200 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4201 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4202 * <p>
4203 * This method throws no reflective or security exceptions.
4204 * @param type the desired target type
4205 * @return a method handle suitable for invoking any method handle of the given type
4206 * @throws IllegalArgumentException if the resulting method handle's type would have
4207 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4208 */
4209 public static MethodHandle exactInvoker(MethodType type) {
4210 return type.invokers().exactInvoker();
4211 }
4212
4213 /**
4214 * Produces a special <em>invoker method handle</em> which can be used to
4215 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4216 * The resulting invoker will have a type which is
4217 * exactly equal to the desired type, except that it will accept
4218 * an additional leading argument of type {@code MethodHandle}.
4219 * <p>
4220 * Before invoking its target, if the target differs from the expected type,
4221 * the invoker will apply reference casts as
4222 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4223 * Similarly, the return value will be converted as necessary.
4224 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4225 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4226 * <p>
4227 * This method is equivalent to the following code (though it may be more efficient):
4228 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4229 * <p style="font-size:smaller;">
4230 * <em>Discussion:</em>
4231 * A {@linkplain MethodType#genericMethodType general method type} is one which
4232 * mentions only {@code Object} arguments and return values.
4233 * An invoker for such a type is capable of calling any method handle
4234 * of the same arity as the general type.
4235 * <p style="font-size:smaller;">
4236 * <em>(Note: The invoker method is not available via the Core Reflection API.
4237 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4238 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4239 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4240 * <p>
4241 * This method throws no reflective or security exceptions.
4242 * @param type the desired target type
4243 * @return a method handle suitable for invoking any method handle convertible to the given type
4244 * @throws IllegalArgumentException if the resulting method handle's type would have
4245 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4246 */
4247 public static MethodHandle invoker(MethodType type) {
4248 return type.invokers().genericInvoker();
4249 }
4250
4251 /**
4252 * Produces a special <em>invoker method handle</em> which can be used to
4253 * invoke a signature-polymorphic access mode method on any VarHandle whose
4254 * associated access mode type is compatible with the given type.
4255 * The resulting invoker will have a type which is exactly equal to the
4256 * desired given type, except that it will accept an additional leading
4257 * argument of type {@code VarHandle}.
4258 *
4259 * @param accessMode the VarHandle access mode
4260 * @param type the desired target type
4261 * @return a method handle suitable for invoking an access mode method of
4262 * any VarHandle whose access mode type is of the given type.
4263 * @since 9
4264 */
4265 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4266 return type.invokers().varHandleMethodExactInvoker(accessMode);
4267 }
4268
4269 /**
4270 * Produces a special <em>invoker method handle</em> which can be used to
4271 * invoke a signature-polymorphic access mode method on any VarHandle whose
4272 * associated access mode type is compatible with the given type.
4273 * The resulting invoker will have a type which is exactly equal to the
4274 * desired given type, except that it will accept an additional leading
4275 * argument of type {@code VarHandle}.
4276 * <p>
4277 * Before invoking its target, if the access mode type differs from the
4278 * desired given type, the invoker will apply reference casts as necessary
4279 * and box, unbox, or widen primitive values, as if by
4280 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4281 * converted as necessary.
4282 * <p>
4283 * This method is equivalent to the following code (though it may be more
4284 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4285 *
4286 * @param accessMode the VarHandle access mode
4287 * @param type the desired target type
4288 * @return a method handle suitable for invoking an access mode method of
4289 * any VarHandle whose access mode type is convertible to the given
4290 * type.
4291 * @since 9
4292 */
4293 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4294 return type.invokers().varHandleMethodInvoker(accessMode);
4295 }
4296
4297 /*non-public*/
4298 static MethodHandle basicInvoker(MethodType type) {
4299 return type.invokers().basicInvoker();
4300 }
4301
4302 /// method handle modification (creation from other method handles)
4303
4304 /**
4305 * Produces a method handle which adapts the type of the
4306 * given method handle to a new type by pairwise argument and return type conversion.
4307 * The original type and new type must have the same number of arguments.
4308 * The resulting method handle is guaranteed to report a type
4309 * which is equal to the desired new type.
4310 * <p>
4311 * If the original type and new type are equal, returns target.
4312 * <p>
4313 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4314 * and some additional conversions are also applied if those conversions fail.
4315 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4316 * if possible, before or instead of any conversions done by {@code asType}:
4317 * <ul>
4318 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4319 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4320 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4321 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4322 * the boolean is converted to a byte value, 1 for true, 0 for false.
4323 * (This treatment follows the usage of the bytecode verifier.)
4324 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4325 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
4326 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4327 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4328 * then a Java casting conversion (JLS 5.5) is applied.
4329 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4330 * widening and/or narrowing.)
4331 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4332 * conversion will be applied at runtime, possibly followed
4333 * by a Java casting conversion (JLS 5.5) on the primitive value,
4334 * possibly followed by a conversion from byte to boolean by testing
4335 * the low-order bit.
4336 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4337 * and if the reference is null at runtime, a zero value is introduced.
4338 * </ul>
4339 * @param target the method handle to invoke after arguments are retyped
4340 * @param newType the expected type of the new method handle
4341 * @return a method handle which delegates to the target after performing
4342 * any necessary argument conversions, and arranges for any
4343 * necessary return value conversions
4344 * @throws NullPointerException if either argument is null
4345 * @throws WrongMethodTypeException if the conversion cannot be made
4346 * @see MethodHandle#asType
4347 */
4348 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4349 explicitCastArgumentsChecks(target, newType);
4350 // use the asTypeCache when possible:
4351 MethodType oldType = target.type();
4352 if (oldType == newType) return target;
4353 if (oldType.explicitCastEquivalentToAsType(newType)) {
4354 return target.asFixedArity().asType(newType);
4355 }
4356 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4357 }
4358
4359 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4360 if (target.type().parameterCount() != newType.parameterCount()) {
4361 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4362 }
4363 }
4364
4365 /**
4366 * Produces a method handle which adapts the calling sequence of the
4367 * given method handle to a new type, by reordering the arguments.
4368 * The resulting method handle is guaranteed to report a type
4369 * which is equal to the desired new type.
4370 * <p>
4371 * The given array controls the reordering.
4372 * Call {@code #I} the number of incoming parameters (the value
4373 * {@code newType.parameterCount()}, and call {@code #O} the number
4374 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4375 * Then the length of the reordering array must be {@code #O},
4376 * and each element must be a non-negative number less than {@code #I}.
4377 * For every {@code N} less than {@code #O}, the {@code N}-th
4378 * outgoing argument will be taken from the {@code I}-th incoming
4379 * argument, where {@code I} is {@code reorder[N]}.
4380 * <p>
4381 * No argument or return value conversions are applied.
4382 * The type of each incoming argument, as determined by {@code newType},
4383 * must be identical to the type of the corresponding outgoing parameter
4384 * or parameters in the target method handle.
4385 * The return type of {@code newType} must be identical to the return
4386 * type of the original target.
4387 * <p>
4388 * The reordering array need not specify an actual permutation.
4389 * An incoming argument will be duplicated if its index appears
4390 * more than once in the array, and an incoming argument will be dropped
4391 * if its index does not appear in the array.
4392 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4393 * incoming arguments which are not mentioned in the reordering array
4394 * may be of any type, as determined only by {@code newType}.
4395 * <blockquote><pre>{@code
4396 import static java.lang.invoke.MethodHandles.*;
4397 import static java.lang.invoke.MethodType.*;
4398 ...
4399 MethodType intfn1 = methodType(int.class, int.class);
4400 MethodType intfn2 = methodType(int.class, int.class, int.class);
4401 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4402 assert(sub.type().equals(intfn2));
4403 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4404 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4405 assert((int)rsub.invokeExact(1, 100) == 99);
4406 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4407 assert(add.type().equals(intfn2));
4408 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4409 assert(twice.type().equals(intfn1));
4410 assert((int)twice.invokeExact(21) == 42);
4411 * }</pre></blockquote>
4412 * <p>
4413 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4414 * variable-arity method handle}, even if the original target method handle was.
4415 * @param target the method handle to invoke after arguments are reordered
4416 * @param newType the expected type of the new method handle
4417 * @param reorder an index array which controls the reordering
4418 * @return a method handle which delegates to the target after it
4419 * drops unused arguments and moves and/or duplicates the other arguments
4420 * @throws NullPointerException if any argument is null
4421 * @throws IllegalArgumentException if the index array length is not equal to
4422 * the arity of the target, or if any index array element
4423 * not a valid index for a parameter of {@code newType},
4424 * or if two corresponding parameter types in
4425 * {@code target.type()} and {@code newType} are not identical,
4426 */
4427 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4428 reorder = reorder.clone(); // get a private copy
4429 MethodType oldType = target.type();
4430 permuteArgumentChecks(reorder, newType, oldType);
4431 // first detect dropped arguments and handle them separately
4432 int[] originalReorder = reorder;
4433 BoundMethodHandle result = target.rebind();
4434 LambdaForm form = result.form;
4435 int newArity = newType.parameterCount();
4436 // Normalize the reordering into a real permutation,
4437 // by removing duplicates and adding dropped elements.
4438 // This somewhat improves lambda form caching, as well
4439 // as simplifying the transform by breaking it up into steps.
4440 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4441 if (ddIdx > 0) {
4442 // We found a duplicated entry at reorder[ddIdx].
4443 // Example: (x,y,z)->asList(x,y,z)
4444 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4445 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4446 // The starred element corresponds to the argument
4447 // deleted by the dupArgumentForm transform.
4448 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4449 boolean killFirst = false;
4450 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4451 // Set killFirst if the dup is larger than an intervening position.
4452 // This will remove at least one inversion from the permutation.
4453 if (dupVal > val) killFirst = true;
4454 }
4455 if (!killFirst) {
4456 srcPos = dstPos;
4457 dstPos = ddIdx;
4458 }
4459 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4460 assert (reorder[srcPos] == reorder[dstPos]);
4461 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4462 // contract the reordering by removing the element at dstPos
4463 int tailPos = dstPos + 1;
4464 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4465 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4466 } else {
4467 int dropVal = ~ddIdx, insPos = 0;
4468 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4469 // Find first element of reorder larger than dropVal.
4470 // This is where we will insert the dropVal.
4471 insPos += 1;
4472 }
4473 Class<?> ptype = newType.parameterType(dropVal);
4474 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4475 oldType = oldType.insertParameterTypes(insPos, ptype);
4476 // expand the reordering by inserting an element at insPos
4477 int tailPos = insPos + 1;
4478 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4479 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4480 reorder[insPos] = dropVal;
4481 }
4482 assert (permuteArgumentChecks(reorder, newType, oldType));
4483 }
4484 assert (reorder.length == newArity); // a perfect permutation
4485 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4486 form = form.editor().permuteArgumentsForm(1, reorder);
4487 if (newType == result.type() && form == result.internalForm())
4488 return result;
4489 return result.copyWith(newType, form);
4490 }
4491
4492 /**
4493 * Return an indication of any duplicate or omission in reorder.
4494 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4495 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4496 * Otherwise, return zero.
4497 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4498 */
4499 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4500 final int BIT_LIMIT = 63; // max number of bits in bit mask
4501 if (newArity < BIT_LIMIT) {
4502 long mask = 0;
4503 for (int i = 0; i < reorder.length; i++) {
4504 int arg = reorder[i];
4505 if (arg >= newArity) {
4506 return reorder.length;
4507 }
4508 long bit = 1L << arg;
4509 if ((mask & bit) != 0) {
4510 return i; // >0 indicates a dup
4511 }
4512 mask |= bit;
4513 }
4514 if (mask == (1L << newArity) - 1) {
4515 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4516 return 0;
4517 }
4518 // find first zero
4519 long zeroBit = Long.lowestOneBit(~mask);
4520 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4521 assert(zeroPos <= newArity);
4522 if (zeroPos == newArity) {
4523 return 0;
4524 }
4525 return ~zeroPos;
4526 } else {
4527 // same algorithm, different bit set
4528 BitSet mask = new BitSet(newArity);
4529 for (int i = 0; i < reorder.length; i++) {
4530 int arg = reorder[i];
4531 if (arg >= newArity) {
4532 return reorder.length;
4533 }
4534 if (mask.get(arg)) {
4535 return i; // >0 indicates a dup
4536 }
4537 mask.set(arg);
4538 }
4539 int zeroPos = mask.nextClearBit(0);
4540 assert(zeroPos <= newArity);
4541 if (zeroPos == newArity) {
4542 return 0;
4543 }
4544 return ~zeroPos;
4545 }
4546 }
4547
4548 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4549 if (newType.returnType() != oldType.returnType())
4550 throw newIllegalArgumentException("return types do not match",
4551 oldType, newType);
4552 if (reorder.length == oldType.parameterCount()) {
4553 int limit = newType.parameterCount();
4554 boolean bad = false;
4555 for (int j = 0; j < reorder.length; j++) {
4556 int i = reorder[j];
4557 if (i < 0 || i >= limit) {
4558 bad = true; break;
4559 }
4560 Class<?> src = newType.parameterType(i);
4561 Class<?> dst = oldType.parameterType(j);
4562 if (src != dst)
4563 throw newIllegalArgumentException("parameter types do not match after reorder",
4564 oldType, newType);
4565 }
4566 if (!bad) return true;
4567 }
4568 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
4569 }
4570
4571 /**
4572 * Produces a method handle of the requested return type which returns the given
4573 * constant value every time it is invoked.
4574 * <p>
4575 * Before the method handle is returned, the passed-in value is converted to the requested type.
4576 * If the requested type is primitive, widening primitive conversions are attempted,
4577 * else reference conversions are attempted.
4578 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4579 * @param type the return type of the desired method handle
4580 * @param value the value to return
4581 * @return a method handle of the given return type and no arguments, which always returns the given value
4582 * @throws NullPointerException if the {@code type} argument is null
4583 * @throws ClassCastException if the value cannot be converted to the required return type
4584 * @throws IllegalArgumentException if the given type is {@code void.class}
4585 */
4586 public static MethodHandle constant(Class<?> type, Object value) {
4587 if (type.isPrimitive()) {
4588 if (type == void.class)
4589 throw newIllegalArgumentException("void type");
4590 Wrapper w = Wrapper.forPrimitiveType(type);
4591 value = w.convert(value, type);
4592 if (w.zero().equals(value))
4593 return zero(w, type);
4594 return insertArguments(identity(type), 0, value);
4595 } else {
4596 if (value == null)
4597 return zero(Wrapper.OBJECT, type);
4598 return identity(type).bindTo(value);
4599 }
4600 }
4601
4602 /**
4603 * Produces a method handle which returns its sole argument when invoked.
4604 * @param type the type of the sole parameter and return value of the desired method handle
4605 * @return a unary method handle which accepts and returns the given type
4606 * @throws NullPointerException if the argument is null
4607 * @throws IllegalArgumentException if the given type is {@code void.class}
4608 */
4609 public static MethodHandle identity(Class<?> type) {
4610 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4611 int pos = btw.ordinal();
4612 MethodHandle ident = IDENTITY_MHS[pos];
4613 if (ident == null) {
4614 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4615 }
4616 if (ident.type().returnType() == type)
4617 return ident;
4618 // something like identity(Foo.class); do not bother to intern these
4619 assert (btw == Wrapper.OBJECT);
4620 return makeIdentity(type);
4621 }
4622
4623 /**
4624 * Produces a constant method handle of the requested return type which
4625 * returns the default value for that type every time it is invoked.
4626 * The resulting constant method handle will have no side effects.
4627 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4628 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4629 * since {@code explicitCastArguments} converts {@code null} to default values.
4630 * @param type the expected return type of the desired method handle
4631 * @return a constant method handle that takes no arguments
4632 * and returns the default value of the given type (or void, if the type is void)
4633 * @throws NullPointerException if the argument is null
4634 * @see MethodHandles#constant
4635 * @see MethodHandles#empty
4636 * @see MethodHandles#explicitCastArguments
4637 * @since 9
4638 */
4639 public static MethodHandle zero(Class<?> type) {
4640 Objects.requireNonNull(type);
4641 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
4642 }
4643
4644 private static MethodHandle identityOrVoid(Class<?> type) {
4645 return type == void.class ? zero(type) : identity(type);
4646 }
4647
4648 /**
4649 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4650 * and returns a suitable default depending on the return type.
4651 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4652 * <p>The returned method handle is equivalent to
4653 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4654 *
4655 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4656 * {@code guardWithTest(pred, target, empty(target.type())}.
4657 * @param type the type of the desired method handle
4658 * @return a constant method handle of the given type, which returns a default value of the given return type
4659 * @throws NullPointerException if the argument is null
4660 * @see MethodHandles#zero
4661 * @see MethodHandles#constant
4662 * @since 9
4663 */
4664 public static MethodHandle empty(MethodType type) {
4665 Objects.requireNonNull(type);
4666 return dropArguments(zero(type.returnType()), 0, type.parameterList());
4667 }
4668
4669 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4670 private static MethodHandle makeIdentity(Class<?> ptype) {
4671 MethodType mtype = methodType(ptype, ptype);
4672 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4673 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4674 }
4675
4676 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
4677 int pos = btw.ordinal();
4678 MethodHandle zero = ZERO_MHS[pos];
4679 if (zero == null) {
4680 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
4681 }
4682 if (zero.type().returnType() == rtype)
4683 return zero;
4684 assert(btw == Wrapper.OBJECT);
4685 return makeZero(rtype);
4686 }
4687 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4688 private static MethodHandle makeZero(Class<?> rtype) {
4689 MethodType mtype = methodType(rtype);
4690 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
4691 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
4692 }
4693
4694 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4695 // Simulate a CAS, to avoid racy duplication of results.
4696 MethodHandle prev = cache[pos];
4697 if (prev != null) return prev;
4698 return cache[pos] = value;
4699 }
4700
4701 /**
4702 * Provides a target method handle with one or more <em>bound arguments</em>
4703 * in advance of the method handle's invocation.
4704 * The formal parameters to the target corresponding to the bound
4705 * arguments are called <em>bound parameters</em>.
4706 * Returns a new method handle which saves away the bound arguments.
4707 * When it is invoked, it receives arguments for any non-bound parameters,
4708 * binds the saved arguments to their corresponding parameters,
4709 * and calls the original target.
4710 * <p>
4711 * The type of the new method handle will drop the types for the bound
4712 * parameters from the original target type, since the new method handle
4713 * will no longer require those arguments to be supplied by its callers.
4714 * <p>
4715 * Each given argument object must match the corresponding bound parameter type.
4716 * If a bound parameter type is a primitive, the argument object
4717 * must be a wrapper, and will be unboxed to produce the primitive value.
4718 * <p>
4719 * The {@code pos} argument selects which parameters are to be bound.
4720 * It may range between zero and <i>N-L</i> (inclusively),
4721 * where <i>N</i> is the arity of the target method handle
4722 * and <i>L</i> is the length of the values array.
4723 * <p>
4724 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4725 * variable-arity method handle}, even if the original target method handle was.
4726 * @param target the method handle to invoke after the argument is inserted
4727 * @param pos where to insert the argument (zero for the first)
4728 * @param values the series of arguments to insert
4729 * @return a method handle which inserts an additional argument,
4730 * before calling the original method handle
4731 * @throws NullPointerException if the target or the {@code values} array is null
4732 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
4733 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4734 * is the length of the values array.
4735 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4736 * type.
4737 * @see MethodHandle#bindTo
4738 */
4739 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4740 int insCount = values.length;
4741 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4742 if (insCount == 0) return target;
4743 BoundMethodHandle result = target.rebind();
4744 for (int i = 0; i < insCount; i++) {
4745 Object value = values[i];
4746 Class<?> ptype = ptypes[pos+i];
4747 if (ptype.isPrimitive()) {
4748 result = insertArgumentPrimitive(result, pos, ptype, value);
4749 } else {
4750 value = ptype.cast(value); // throw CCE if needed
4751 result = result.bindArgumentL(pos, value);
4752 }
4753 }
4754 return result;
4755 }
4756
4757 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4758 Class<?> ptype, Object value) {
4759 Wrapper w = Wrapper.forPrimitiveType(ptype);
4760 // perform unboxing and/or primitive conversion
4761 value = w.convert(value, ptype);
4762 switch (w) {
4763 case INT: return result.bindArgumentI(pos, (int)value);
4764 case LONG: return result.bindArgumentJ(pos, (long)value);
4765 case FLOAT: return result.bindArgumentF(pos, (float)value);
4766 case DOUBLE: return result.bindArgumentD(pos, (double)value);
4767 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
4768 }
4769 }
4770
4771 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
4772 MethodType oldType = target.type();
4773 int outargs = oldType.parameterCount();
4774 int inargs = outargs - insCount;
4775 if (inargs < 0)
4776 throw newIllegalArgumentException("too many values to insert");
4777 if (pos < 0 || pos > inargs)
4778 throw newIllegalArgumentException("no argument type to append");
4779 return oldType.ptypes();
4780 }
4781
4782 /**
4783 * Produces a method handle which will discard some dummy arguments
4784 * before calling some other specified <i>target</i> method handle.
4785 * The type of the new method handle will be the same as the target's type,
4786 * except it will also include the dummy argument types,
4787 * at some given position.
4788 * <p>
4789 * The {@code pos} argument may range between zero and <i>N</i>,
4790 * where <i>N</i> is the arity of the target.
4791 * If {@code pos} is zero, the dummy arguments will precede
4792 * the target's real arguments; if {@code pos} is <i>N</i>
4793 * they will come after.
4794 * <p>
4795 * <b>Example:</b>
4796 * <blockquote><pre>{@code
4797 import static java.lang.invoke.MethodHandles.*;
4798 import static java.lang.invoke.MethodType.*;
4799 ...
4800 MethodHandle cat = lookup().findVirtual(String.class,
4801 "concat", methodType(String.class, String.class));
4802 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4803 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
4804 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
4805 assertEquals(bigType, d0.type());
4806 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
4807 * }</pre></blockquote>
4808 * <p>
4809 * This method is also equivalent to the following code:
4810 * <blockquote><pre>
4811 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
4812 * </pre></blockquote>
4813 * @param target the method handle to invoke after the arguments are dropped
4814 * @param pos position of first argument to drop (zero for the leftmost)
4815 * @param valueTypes the type(s) of the argument(s) to drop
4816 * @return a method handle which drops arguments of the given types,
4817 * before calling the original method handle
4818 * @throws NullPointerException if the target is null,
4819 * or if the {@code valueTypes} list or any of its elements is null
4820 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4821 * or if {@code pos} is negative or greater than the arity of the target,
4822 * or if the new method handle's type would have too many parameters
4823 */
4824 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4825 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
4826 }
4827
4828 private static List<Class<?>> copyTypes(Object[] array) {
4829 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
4830 }
4831
4832 private static MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4833 MethodType oldType = target.type(); // get NPE
4834 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
4835 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
4836 if (dropped == 0) return target;
4837 BoundMethodHandle result = target.rebind();
4838 LambdaForm lform = result.form;
4839 int insertFormArg = 1 + pos;
4840 for (Class<?> ptype : valueTypes) {
4841 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
4842 }
4843 result = result.copyWith(newType, lform);
4844 return result;
4845 }
4846
4847 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
4848 int dropped = valueTypes.size();
4849 MethodType.checkSlotCount(dropped);
4850 int outargs = oldType.parameterCount();
4851 int inargs = outargs + dropped;
4852 if (pos < 0 || pos > outargs)
4853 throw newIllegalArgumentException("no argument type to remove"
4854 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
4855 );
4856 return dropped;
4857 }
4858
4859 /**
4860 * Produces a method handle which will discard some dummy arguments
4861 * before calling some other specified <i>target</i> method handle.
4862 * The type of the new method handle will be the same as the target's type,
4863 * except it will also include the dummy argument types,
4864 * at some given position.
4865 * <p>
4866 * The {@code pos} argument may range between zero and <i>N</i>,
4867 * where <i>N</i> is the arity of the target.
4868 * If {@code pos} is zero, the dummy arguments will precede
4869 * the target's real arguments; if {@code pos} is <i>N</i>
4870 * they will come after.
4871 * @apiNote
4872 * <blockquote><pre>{@code
4873 import static java.lang.invoke.MethodHandles.*;
4874 import static java.lang.invoke.MethodType.*;
4875 ...
4876 MethodHandle cat = lookup().findVirtual(String.class,
4877 "concat", methodType(String.class, String.class));
4878 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4879 MethodHandle d0 = dropArguments(cat, 0, String.class);
4880 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
4881 MethodHandle d1 = dropArguments(cat, 1, String.class);
4882 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4883 MethodHandle d2 = dropArguments(cat, 2, String.class);
4884 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4885 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4886 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4887 * }</pre></blockquote>
4888 * <p>
4889 * This method is also equivalent to the following code:
4890 * <blockquote><pre>
4891 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4892 * </pre></blockquote>
4893 * @param target the method handle to invoke after the arguments are dropped
4894 * @param pos position of first argument to drop (zero for the leftmost)
4895 * @param valueTypes the type(s) of the argument(s) to drop
4896 * @return a method handle which drops arguments of the given types,
4897 * before calling the original method handle
4898 * @throws NullPointerException if the target is null,
4899 * or if the {@code valueTypes} array or any of its elements is null
4900 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4901 * or if {@code pos} is negative or greater than the arity of the target,
4902 * or if the new method handle's type would have
4903 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4904 */
4905 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4906 return dropArguments0(target, pos, copyTypes(valueTypes));
4907 }
4908
4909 // private version which allows caller some freedom with error handling
4910 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4911 boolean nullOnFailure) {
4912 newTypes = copyTypes(newTypes.toArray());
4913 List<Class<?>> oldTypes = target.type().parameterList();
4914 int match = oldTypes.size();
4915 if (skip != 0) {
4916 if (skip < 0 || skip > match) {
4917 throw newIllegalArgumentException("illegal skip", skip, target);
4918 }
4919 oldTypes = oldTypes.subList(skip, match);
4920 match -= skip;
4921 }
4922 List<Class<?>> addTypes = newTypes;
4923 int add = addTypes.size();
4924 if (pos != 0) {
4925 if (pos < 0 || pos > add) {
4926 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4927 }
4928 addTypes = addTypes.subList(pos, add);
4929 add -= pos;
4930 assert(addTypes.size() == add);
4931 }
4932 // Do not add types which already match the existing arguments.
4933 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4934 if (nullOnFailure) {
4935 return null;
4936 }
4937 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
4938 }
4939 addTypes = addTypes.subList(match, add);
4940 add -= match;
4941 assert(addTypes.size() == add);
4942 // newTypes: ( P*[pos], M*[match], A*[add] )
4943 // target: ( S*[skip], M*[match] )
4944 MethodHandle adapter = target;
4945 if (add > 0) {
4946 adapter = dropArguments0(adapter, skip+ match, addTypes);
4947 }
4948 // adapter: (S*[skip], M*[match], A*[add] )
4949 if (pos > 0) {
4950 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
4951 }
4952 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
4953 return adapter;
4954 }
4955
4956 /**
4957 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
4958 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
4959 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
4960 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
4961 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
4962 * {@link #dropArguments(MethodHandle, int, Class[])}.
4963 * <p>
4964 * The resulting handle will have the same return type as the target handle.
4965 * <p>
4966 * In more formal terms, assume these two type lists:<ul>
4967 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
4968 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
4969 * {@code newTypes}.
4970 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
4971 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
4972 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
4973 * sub-list.
4974 * </ul>
4975 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
4976 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
4977 * {@link #dropArguments(MethodHandle, int, Class[])}.
4978 *
4979 * @apiNote
4980 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
4981 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
4982 * <blockquote><pre>{@code
4983 import static java.lang.invoke.MethodHandles.*;
4984 import static java.lang.invoke.MethodType.*;
4985 ...
4986 ...
4987 MethodHandle h0 = constant(boolean.class, true);
4988 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
4989 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
4990 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
4991 if (h1.type().parameterCount() < h2.type().parameterCount())
4992 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
4993 else
4994 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
4995 MethodHandle h3 = guardWithTest(h0, h1, h2);
4996 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
4997 * }</pre></blockquote>
4998 * @param target the method handle to adapt
4999 * @param skip number of targets parameters to disregard (they will be unchanged)
5000 * @param newTypes the list of types to match {@code target}'s parameter type list to
5001 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5002 * @return a possibly adapted method handle
5003 * @throws NullPointerException if either argument is null
5004 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5005 * or if {@code skip} is negative or greater than the arity of the target,
5006 * or if {@code pos} is negative or greater than the newTypes list size,
5007 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5008 * {@code pos}.
5009 * @since 9
5010 */
5011 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5012 Objects.requireNonNull(target);
5013 Objects.requireNonNull(newTypes);
5014 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
5015 }
5016
5017 /**
5018 * Adapts a target method handle by pre-processing
5019 * one or more of its arguments, each with its own unary filter function,
5020 * and then calling the target with each pre-processed argument
5021 * replaced by the result of its corresponding filter function.
5022 * <p>
5023 * The pre-processing is performed by one or more method handles,
5024 * specified in the elements of the {@code filters} array.
5025 * The first element of the filter array corresponds to the {@code pos}
5026 * argument of the target, and so on in sequence.
5027 * The filter functions are invoked in left to right order.
5028 * <p>
5029 * Null arguments in the array are treated as identity functions,
5030 * and the corresponding arguments left unchanged.
5031 * (If there are no non-null elements in the array, the original target is returned.)
5032 * Each filter is applied to the corresponding argument of the adapter.
5033 * <p>
5034 * If a filter {@code F} applies to the {@code N}th argument of
5035 * the target, then {@code F} must be a method handle which
5036 * takes exactly one argument. The type of {@code F}'s sole argument
5037 * replaces the corresponding argument type of the target
5038 * in the resulting adapted method handle.
5039 * The return type of {@code F} must be identical to the corresponding
5040 * parameter type of the target.
5041 * <p>
5042 * It is an error if there are elements of {@code filters}
5043 * (null or not)
5044 * which do not correspond to argument positions in the target.
5045 * <p><b>Example:</b>
5046 * <blockquote><pre>{@code
5047 import static java.lang.invoke.MethodHandles.*;
5048 import static java.lang.invoke.MethodType.*;
5049 ...
5050 MethodHandle cat = lookup().findVirtual(String.class,
5051 "concat", methodType(String.class, String.class));
5052 MethodHandle upcase = lookup().findVirtual(String.class,
5053 "toUpperCase", methodType(String.class));
5054 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5055 MethodHandle f0 = filterArguments(cat, 0, upcase);
5056 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5057 MethodHandle f1 = filterArguments(cat, 1, upcase);
5058 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5059 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5060 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5061 * }</pre></blockquote>
5062 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5063 * denotes the return type of both the {@code target} and resulting adapter.
5064 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5065 * of the parameters and arguments that precede and follow the filter position
5066 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5067 * values of the filtered parameters and arguments; they also represent the
5068 * return types of the {@code filter[i]} handles. The latter accept arguments
5069 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5070 * the resulting adapter.
5071 * <blockquote><pre>{@code
5072 * T target(P... p, A[i]... a[i], B... b);
5073 * A[i] filter[i](V[i]);
5074 * T adapter(P... p, V[i]... v[i], B... b) {
5075 * return target(p..., filter[i](v[i])..., b...);
5076 * }
5077 * }</pre></blockquote>
5078 * <p>
5079 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5080 * variable-arity method handle}, even if the original target method handle was.
5081 *
5082 * @param target the method handle to invoke after arguments are filtered
5083 * @param pos the position of the first argument to filter
5084 * @param filters method handles to call initially on filtered arguments
5085 * @return method handle which incorporates the specified argument filtering logic
5086 * @throws NullPointerException if the target is null
5087 * or if the {@code filters} array is null
5088 * @throws IllegalArgumentException if a non-null element of {@code filters}
5089 * does not match a corresponding argument type of target as described above,
5090 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5091 * or if the resulting method handle's type would have
5092 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5093 */
5094 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5095 // In method types arguments start at index 0, while the LF
5096 // editor have the MH receiver at position 0 - adjust appropriately.
5097 final int MH_RECEIVER_OFFSET = 1;
5098 filterArgumentsCheckArity(target, pos, filters);
5099 MethodHandle adapter = target;
5100
5101 // keep track of currently matched filters, as to optimize repeated filters
5102 int index = 0;
5103 int[] positions = new int[filters.length];
5104 MethodHandle filter = null;
5105
5106 // process filters in reverse order so that the invocation of
5107 // the resulting adapter will invoke the filters in left-to-right order
5108 for (int i = filters.length - 1; i >= 0; --i) {
5109 MethodHandle newFilter = filters[i];
5110 if (newFilter == null) continue; // ignore null elements of filters
5111
5112 // flush changes on update
5113 if (filter != newFilter) {
5114 if (filter != null) {
5115 if (index > 1) {
5116 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5117 } else {
5118 adapter = filterArgument(adapter, positions[0] - 1, filter);
5119 }
5120 }
5121 filter = newFilter;
5122 index = 0;
5123 }
5124
5125 filterArgumentChecks(target, pos + i, newFilter);
5126 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5127 }
5128 if (index > 1) {
5129 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5130 } else if (index == 1) {
5131 adapter = filterArgument(adapter, positions[0] - 1, filter);
5132 }
5133 return adapter;
5134 }
5135
5136 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5137 MethodType targetType = adapter.type();
5138 MethodType filterType = filter.type();
5139 BoundMethodHandle result = adapter.rebind();
5140 Class<?> newParamType = filterType.parameterType(0);
5141
5142 Class<?>[] ptypes = targetType.ptypes().clone();
5143 for (int pos : positions) {
5144 ptypes[pos - 1] = newParamType;
5145 }
5146 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
5147
5148 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5149 return result.copyWithExtendL(newType, lform, filter);
5150 }
5151
5152 /*non-public*/
5153 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5154 filterArgumentChecks(target, pos, filter);
5155 MethodType targetType = target.type();
5156 MethodType filterType = filter.type();
5157 BoundMethodHandle result = target.rebind();
5158 Class<?> newParamType = filterType.parameterType(0);
5159 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5160 MethodType newType = targetType.changeParameterType(pos, newParamType);
5161 result = result.copyWithExtendL(newType, lform, filter);
5162 return result;
5163 }
5164
5165 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5166 MethodType targetType = target.type();
5167 int maxPos = targetType.parameterCount();
5168 if (pos + filters.length > maxPos)
5169 throw newIllegalArgumentException("too many filters");
5170 }
5171
5172 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5173 MethodType targetType = target.type();
5174 MethodType filterType = filter.type();
5175 if (filterType.parameterCount() != 1
5176 || filterType.returnType() != targetType.parameterType(pos))
5177 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5178 }
5179
5180 /**
5181 * Adapts a target method handle by pre-processing
5182 * a sub-sequence of its arguments with a filter (another method handle).
5183 * The pre-processed arguments are replaced by the result (if any) of the
5184 * filter function.
5185 * The target is then called on the modified (usually shortened) argument list.
5186 * <p>
5187 * If the filter returns a value, the target must accept that value as
5188 * its argument in position {@code pos}, preceded and/or followed by
5189 * any arguments not passed to the filter.
5190 * If the filter returns void, the target must accept all arguments
5191 * not passed to the filter.
5192 * No arguments are reordered, and a result returned from the filter
5193 * replaces (in order) the whole subsequence of arguments originally
5194 * passed to the adapter.
5195 * <p>
5196 * The argument types (if any) of the filter
5197 * replace zero or one argument types of the target, at position {@code pos},
5198 * in the resulting adapted method handle.
5199 * The return type of the filter (if any) must be identical to the
5200 * argument type of the target at position {@code pos}, and that target argument
5201 * is supplied by the return value of the filter.
5202 * <p>
5203 * In all cases, {@code pos} must be greater than or equal to zero, and
5204 * {@code pos} must also be less than or equal to the target's arity.
5205 * <p><b>Example:</b>
5206 * <blockquote><pre>{@code
5207 import static java.lang.invoke.MethodHandles.*;
5208 import static java.lang.invoke.MethodType.*;
5209 ...
5210 MethodHandle deepToString = publicLookup()
5211 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5212
5213 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5214 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5215
5216 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5217 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5218
5219 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5220 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5221 assertEquals("[top, [up, down], strange]",
5222 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5223
5224 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5225 assertEquals("[top, [up, down], [strange]]",
5226 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5227
5228 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5229 assertEquals("[top, [[up, down, strange], charm], bottom]",
5230 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5231 * }</pre></blockquote>
5232 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5233 * represents the return type of the {@code target} and resulting adapter.
5234 * {@code V}/{@code v} stand for the return type and value of the
5235 * {@code filter}, which are also found in the signature and arguments of
5236 * the {@code target}, respectively, unless {@code V} is {@code void}.
5237 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5238 * and values preceding and following the collection position, {@code pos},
5239 * in the {@code target}'s signature. They also turn up in the resulting
5240 * adapter's signature and arguments, where they surround
5241 * {@code B}/{@code b}, which represent the parameter types and arguments
5242 * to the {@code filter} (if any).
5243 * <blockquote><pre>{@code
5244 * T target(A...,V,C...);
5245 * V filter(B...);
5246 * T adapter(A... a,B... b,C... c) {
5247 * V v = filter(b...);
5248 * return target(a...,v,c...);
5249 * }
5250 * // and if the filter has no arguments:
5251 * T target2(A...,V,C...);
5252 * V filter2();
5253 * T adapter2(A... a,C... c) {
5254 * V v = filter2();
5255 * return target2(a...,v,c...);
5256 * }
5257 * // and if the filter has a void return:
5258 * T target3(A...,C...);
5259 * void filter3(B...);
5260 * T adapter3(A... a,B... b,C... c) {
5261 * filter3(b...);
5262 * return target3(a...,c...);
5263 * }
5264 * }</pre></blockquote>
5265 * <p>
5266 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5267 * one which first "folds" the affected arguments, and then drops them, in separate
5268 * steps as follows:
5269 * <blockquote><pre>{@code
5270 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5271 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5272 * }</pre></blockquote>
5273 * If the target method handle consumes no arguments besides than the result
5274 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5275 * is equivalent to {@code filterReturnValue(coll, mh)}.
5276 * If the filter method handle {@code coll} consumes one argument and produces
5277 * a non-void result, then {@code collectArguments(mh, N, coll)}
5278 * is equivalent to {@code filterArguments(mh, N, coll)}.
5279 * Other equivalences are possible but would require argument permutation.
5280 * <p>
5281 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5282 * variable-arity method handle}, even if the original target method handle was.
5283 *
5284 * @param target the method handle to invoke after filtering the subsequence of arguments
5285 * @param pos the position of the first adapter argument to pass to the filter,
5286 * and/or the target argument which receives the result of the filter
5287 * @param filter method handle to call on the subsequence of arguments
5288 * @return method handle which incorporates the specified argument subsequence filtering logic
5289 * @throws NullPointerException if either argument is null
5290 * @throws IllegalArgumentException if the return type of {@code filter}
5291 * is non-void and is not the same as the {@code pos} argument of the target,
5292 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5293 * or if the resulting method handle's type would have
5294 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5295 * @see MethodHandles#foldArguments
5296 * @see MethodHandles#filterArguments
5297 * @see MethodHandles#filterReturnValue
5298 */
5299 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5300 MethodType newType = collectArgumentsChecks(target, pos, filter);
5301 MethodType collectorType = filter.type();
5302 BoundMethodHandle result = target.rebind();
5303 LambdaForm lform;
5304 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
5305 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
5306 if (lform != null) {
5307 return result.copyWith(newType, lform);
5308 }
5309 }
5310 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5311 return result.copyWithExtendL(newType, lform, filter);
5312 }
5313
5314 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5315 MethodType targetType = target.type();
5316 MethodType filterType = filter.type();
5317 Class<?> rtype = filterType.returnType();
5318 List<Class<?>> filterArgs = filterType.parameterList();
5319 if (rtype == void.class) {
5320 return targetType.insertParameterTypes(pos, filterArgs);
5321 }
5322 if (rtype != targetType.parameterType(pos)) {
5323 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5324 }
5325 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
5326 }
5327
5328 /**
5329 * Adapts a target method handle by post-processing
5330 * its return value (if any) with a filter (another method handle).
5331 * The result of the filter is returned from the adapter.
5332 * <p>
5333 * If the target returns a value, the filter must accept that value as
5334 * its only argument.
5335 * If the target returns void, the filter must accept no arguments.
5336 * <p>
5337 * The return type of the filter
5338 * replaces the return type of the target
5339 * in the resulting adapted method handle.
5340 * The argument type of the filter (if any) must be identical to the
5341 * return type of the target.
5342 * <p><b>Example:</b>
5343 * <blockquote><pre>{@code
5344 import static java.lang.invoke.MethodHandles.*;
5345 import static java.lang.invoke.MethodType.*;
5346 ...
5347 MethodHandle cat = lookup().findVirtual(String.class,
5348 "concat", methodType(String.class, String.class));
5349 MethodHandle length = lookup().findVirtual(String.class,
5350 "length", methodType(int.class));
5351 System.out.println((String) cat.invokeExact("x", "y")); // xy
5352 MethodHandle f0 = filterReturnValue(cat, length);
5353 System.out.println((int) f0.invokeExact("x", "y")); // 2
5354 * }</pre></blockquote>
5355 * <p>Here is pseudocode for the resulting adapter. In the code,
5356 * {@code T}/{@code t} represent the result type and value of the
5357 * {@code target}; {@code V}, the result type of the {@code filter}; and
5358 * {@code A}/{@code a}, the types and values of the parameters and arguments
5359 * of the {@code target} as well as the resulting adapter.
5360 * <blockquote><pre>{@code
5361 * T target(A...);
5362 * V filter(T);
5363 * V adapter(A... a) {
5364 * T t = target(a...);
5365 * return filter(t);
5366 * }
5367 * // and if the target has a void return:
5368 * void target2(A...);
5369 * V filter2();
5370 * V adapter2(A... a) {
5371 * target2(a...);
5372 * return filter2();
5373 * }
5374 * // and if the filter has a void return:
5375 * T target3(A...);
5376 * void filter3(V);
5377 * void adapter3(A... a) {
5378 * T t = target3(a...);
5379 * filter3(t);
5380 * }
5381 * }</pre></blockquote>
5382 * <p>
5383 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5384 * variable-arity method handle}, even if the original target method handle was.
5385 * @param target the method handle to invoke before filtering the return value
5386 * @param filter method handle to call on the return value
5387 * @return method handle which incorporates the specified return value filtering logic
5388 * @throws NullPointerException if either argument is null
5389 * @throws IllegalArgumentException if the argument list of {@code filter}
5390 * does not match the return type of target as described above
5391 */
5392 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5393 MethodType targetType = target.type();
5394 MethodType filterType = filter.type();
5395 filterReturnValueChecks(targetType, filterType);
5396 BoundMethodHandle result = target.rebind();
5397 BasicType rtype = BasicType.basicType(filterType.returnType());
5398 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5399 MethodType newType = targetType.changeReturnType(filterType.returnType());
5400 result = result.copyWithExtendL(newType, lform, filter);
5401 return result;
5402 }
5403
5404 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5405 Class<?> rtype = targetType.returnType();
5406 int filterValues = filterType.parameterCount();
5407 if (filterValues == 0
5408 ? (rtype != void.class)
5409 : (rtype != filterType.parameterType(0) || filterValues != 1))
5410 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5411 }
5412
5413 /**
5414 * Adapts a target method handle by pre-processing
5415 * some of its arguments, and then calling the target with
5416 * the result of the pre-processing, inserted into the original
5417 * sequence of arguments.
5418 * <p>
5419 * The pre-processing is performed by {@code combiner}, a second method handle.
5420 * Of the arguments passed to the adapter, the first {@code N} arguments
5421 * are copied to the combiner, which is then called.
5422 * (Here, {@code N} is defined as the parameter count of the combiner.)
5423 * After this, control passes to the target, with any result
5424 * from the combiner inserted before the original {@code N} incoming
5425 * arguments.
5426 * <p>
5427 * If the combiner returns a value, the first parameter type of the target
5428 * must be identical with the return type of the combiner, and the next
5429 * {@code N} parameter types of the target must exactly match the parameters
5430 * of the combiner.
5431 * <p>
5432 * If the combiner has a void return, no result will be inserted,
5433 * and the first {@code N} parameter types of the target
5434 * must exactly match the parameters of the combiner.
5435 * <p>
5436 * The resulting adapter is the same type as the target, except that the
5437 * first parameter type is dropped,
5438 * if it corresponds to the result of the combiner.
5439 * <p>
5440 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5441 * that either the combiner or the target does not wish to receive.
5442 * If some of the incoming arguments are destined only for the combiner,
5443 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5444 * arguments will not need to be live on the stack on entry to the
5445 * target.)
5446 * <p><b>Example:</b>
5447 * <blockquote><pre>{@code
5448 import static java.lang.invoke.MethodHandles.*;
5449 import static java.lang.invoke.MethodType.*;
5450 ...
5451 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5452 "println", methodType(void.class, String.class))
5453 .bindTo(System.out);
5454 MethodHandle cat = lookup().findVirtual(String.class,
5455 "concat", methodType(String.class, String.class));
5456 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5457 MethodHandle catTrace = foldArguments(cat, trace);
5458 // also prints "boo":
5459 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5460 * }</pre></blockquote>
5461 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5462 * represents the result type of the {@code target} and resulting adapter.
5463 * {@code V}/{@code v} represent the type and value of the parameter and argument
5464 * of {@code target} that precedes the folding position; {@code V} also is
5465 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5466 * types and values of the {@code N} parameters and arguments at the folding
5467 * position. {@code B}/{@code b} represent the types and values of the
5468 * {@code target} parameters and arguments that follow the folded parameters
5469 * and arguments.
5470 * <blockquote><pre>{@code
5471 * // there are N arguments in A...
5472 * T target(V, A[N]..., B...);
5473 * V combiner(A...);
5474 * T adapter(A... a, B... b) {
5475 * V v = combiner(a...);
5476 * return target(v, a..., b...);
5477 * }
5478 * // and if the combiner has a void return:
5479 * T target2(A[N]..., B...);
5480 * void combiner2(A...);
5481 * T adapter2(A... a, B... b) {
5482 * combiner2(a...);
5483 * return target2(a..., b...);
5484 * }
5485 * }</pre></blockquote>
5486 * <p>
5487 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5488 * variable-arity method handle}, even if the original target method handle was.
5489 * @param target the method handle to invoke after arguments are combined
5490 * @param combiner method handle to call initially on the incoming arguments
5491 * @return method handle which incorporates the specified argument folding logic
5492 * @throws NullPointerException if either argument is null
5493 * @throws IllegalArgumentException if {@code combiner}'s return type
5494 * is non-void and not the same as the first argument type of
5495 * the target, or if the initial {@code N} argument types
5496 * of the target
5497 * (skipping one matching the {@code combiner}'s return type)
5498 * are not identical with the argument types of {@code combiner}
5499 */
5500 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5501 return foldArguments(target, 0, combiner);
5502 }
5503
5504 /**
5505 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5506 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5507 * before the folded arguments.
5508 * <p>
5509 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5510 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5511 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5512 * 0.
5513 *
5514 * @apiNote Example:
5515 * <blockquote><pre>{@code
5516 import static java.lang.invoke.MethodHandles.*;
5517 import static java.lang.invoke.MethodType.*;
5518 ...
5519 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5520 "println", methodType(void.class, String.class))
5521 .bindTo(System.out);
5522 MethodHandle cat = lookup().findVirtual(String.class,
5523 "concat", methodType(String.class, String.class));
5524 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5525 MethodHandle catTrace = foldArguments(cat, 1, trace);
5526 // also prints "jum":
5527 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5528 * }</pre></blockquote>
5529 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5530 * represents the result type of the {@code target} and resulting adapter.
5531 * {@code V}/{@code v} represent the type and value of the parameter and argument
5532 * of {@code target} that precedes the folding position; {@code V} also is
5533 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5534 * types and values of the {@code N} parameters and arguments at the folding
5535 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5536 * and values of the {@code target} parameters and arguments that precede and
5537 * follow the folded parameters and arguments starting at {@code pos},
5538 * respectively.
5539 * <blockquote><pre>{@code
5540 * // there are N arguments in A...
5541 * T target(Z..., V, A[N]..., B...);
5542 * V combiner(A...);
5543 * T adapter(Z... z, A... a, B... b) {
5544 * V v = combiner(a...);
5545 * return target(z..., v, a..., b...);
5546 * }
5547 * // and if the combiner has a void return:
5548 * T target2(Z..., A[N]..., B...);
5549 * void combiner2(A...);
5550 * T adapter2(Z... z, A... a, B... b) {
5551 * combiner2(a...);
5552 * return target2(z..., a..., b...);
5553 * }
5554 * }</pre></blockquote>
5555 * <p>
5556 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5557 * variable-arity method handle}, even if the original target method handle was.
5558 *
5559 * @param target the method handle to invoke after arguments are combined
5560 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5561 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5562 * @param combiner method handle to call initially on the incoming arguments
5563 * @return method handle which incorporates the specified argument folding logic
5564 * @throws NullPointerException if either argument is null
5565 * @throws IllegalArgumentException if either of the following two conditions holds:
5566 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5567 * {@code pos} of the target signature;
5568 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5569 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5570 *
5571 * @see #foldArguments(MethodHandle, MethodHandle)
5572 * @since 9
5573 */
5574 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5575 MethodType targetType = target.type();
5576 MethodType combinerType = combiner.type();
5577 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5578 BoundMethodHandle result = target.rebind();
5579 boolean dropResult = rtype == void.class;
5580 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5581 MethodType newType = targetType;
5582 if (!dropResult) {
5583 newType = newType.dropParameterTypes(pos, pos + 1);
5584 }
5585 result = result.copyWithExtendL(newType, lform, combiner);
5586 return result;
5587 }
5588
5589 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5590 int foldArgs = combinerType.parameterCount();
5591 Class<?> rtype = combinerType.returnType();
5592 int foldVals = rtype == void.class ? 0 : 1;
5593 int afterInsertPos = foldPos + foldVals;
5594 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5595 if (ok) {
5596 for (int i = 0; i < foldArgs; i++) {
5597 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5598 ok = false;
5599 break;
5600 }
5601 }
5602 }
5603 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5604 ok = false;
5605 if (!ok)
5606 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5607 return rtype;
5608 }
5609
5610 /**
5611 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5612 * of the pre-processing replacing the argument at the given position.
5613 *
5614 * @param target the method handle to invoke after arguments are combined
5615 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5616 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5617 * @param combiner method handle to call initially on the incoming arguments
5618 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5619 * @return method handle which incorporates the specified argument folding logic
5620 * @throws NullPointerException if either argument is null
5621 * @throws IllegalArgumentException if either of the following two conditions holds:
5622 * (1) {@code combiner}'s return type is not the same as the argument type at position
5623 * {@code pos} of the target signature;
5624 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5625 * not identical with the argument types of {@code combiner}.
5626 */
5627 /*non-public*/
5628 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5629 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5630 }
5631
5632 /**
5633 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5634 * the pre-processing inserted into the original sequence of arguments at the given position.
5635 *
5636 * @param target the method handle to invoke after arguments are combined
5637 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5638 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5639 * @param combiner method handle to call initially on the incoming arguments
5640 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5641 * @return method handle which incorporates the specified argument folding logic
5642 * @throws NullPointerException if either argument is null
5643 * @throws IllegalArgumentException if either of the following two conditions holds:
5644 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5645 * {@code pos} of the target signature;
5646 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5647 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5648 * with the argument types of {@code combiner}.
5649 */
5650 /*non-public*/
5651 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5652 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5653 }
5654
5655 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5656 MethodType targetType = target.type();
5657 MethodType combinerType = combiner.type();
5658 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5659 BoundMethodHandle result = target.rebind();
5660
5661 MethodType newType = targetType;
5662 LambdaForm lform;
5663 if (filter) {
5664 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5665 } else {
5666 boolean dropResult = rtype == void.class;
5667 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5668 if (!dropResult) {
5669 newType = newType.dropParameterTypes(position, position + 1);
5670 }
5671 }
5672 result = result.copyWithExtendL(newType, lform, combiner);
5673 return result;
5674 }
5675
5676 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5677 int combinerArgs = combinerType.parameterCount();
5678 if (argPos.length != combinerArgs) {
5679 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5680 }
5681 Class<?> rtype = combinerType.returnType();
5682
5683 for (int i = 0; i < combinerArgs; i++) {
5684 int arg = argPos[i];
5685 if (arg < 0 || arg > targetType.parameterCount()) {
5686 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5687 }
5688 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5689 throw newIllegalArgumentException("target argument type at position " + arg
5690 + " must match combiner argument type at index " + i + ": " + targetType
5691 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5692 }
5693 }
5694 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5695 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5696 }
5697 return rtype;
5698 }
5699
5700 /**
5701 * Makes a method handle which adapts a target method handle,
5702 * by guarding it with a test, a boolean-valued method handle.
5703 * If the guard fails, a fallback handle is called instead.
5704 * All three method handles must have the same corresponding
5705 * argument and return types, except that the return type
5706 * of the test must be boolean, and the test is allowed
5707 * to have fewer arguments than the other two method handles.
5708 * <p>
5709 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5710 * represents the uniform result type of the three involved handles;
5711 * {@code A}/{@code a}, the types and values of the {@code target}
5712 * parameters and arguments that are consumed by the {@code test}; and
5713 * {@code B}/{@code b}, those types and values of the {@code target}
5714 * parameters and arguments that are not consumed by the {@code test}.
5715 * <blockquote><pre>{@code
5716 * boolean test(A...);
5717 * T target(A...,B...);
5718 * T fallback(A...,B...);
5719 * T adapter(A... a,B... b) {
5720 * if (test(a...))
5721 * return target(a..., b...);
5722 * else
5723 * return fallback(a..., b...);
5724 * }
5725 * }</pre></blockquote>
5726 * Note that the test arguments ({@code a...} in the pseudocode) cannot
5727 * be modified by execution of the test, and so are passed unchanged
5728 * from the caller to the target or fallback as appropriate.
5729 * @param test method handle used for test, must return boolean
5730 * @param target method handle to call if test passes
5731 * @param fallback method handle to call if test fails
5732 * @return method handle which incorporates the specified if/then/else logic
5733 * @throws NullPointerException if any argument is null
5734 * @throws IllegalArgumentException if {@code test} does not return boolean,
5735 * or if all three method types do not match (with the return
5736 * type of {@code test} changed to match that of the target).
5737 */
5738 public static MethodHandle guardWithTest(MethodHandle test,
5739 MethodHandle target,
5740 MethodHandle fallback) {
5741 MethodType gtype = test.type();
5742 MethodType ttype = target.type();
5743 MethodType ftype = fallback.type();
5744 if (!ttype.equals(ftype))
5745 throw misMatchedTypes("target and fallback types", ttype, ftype);
5746 if (gtype.returnType() != boolean.class)
5747 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
5748 List<Class<?>> targs = ttype.parameterList();
5749 test = dropArgumentsToMatch(test, 0, targs, 0, true);
5750 if (test == null) {
5751 throw misMatchedTypes("target and test types", ttype, gtype);
5752 }
5753 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
5754 }
5755
5756 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
5757 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
5758 }
5759
5760 /**
5761 * Makes a method handle which adapts a target method handle,
5762 * by running it inside an exception handler.
5763 * If the target returns normally, the adapter returns that value.
5764 * If an exception matching the specified type is thrown, the fallback
5765 * handle is called instead on the exception, plus the original arguments.
5766 * <p>
5767 * The target and handler must have the same corresponding
5768 * argument and return types, except that handler may omit trailing arguments
5769 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
5770 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
5771 * <p>
5772 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5773 * represents the return type of the {@code target} and {@code handler},
5774 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
5775 * the types and values of arguments to the resulting handle consumed by
5776 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
5777 * resulting handle discarded by {@code handler}.
5778 * <blockquote><pre>{@code
5779 * T target(A..., B...);
5780 * T handler(ExType, A...);
5781 * T adapter(A... a, B... b) {
5782 * try {
5783 * return target(a..., b...);
5784 * } catch (ExType ex) {
5785 * return handler(ex, a...);
5786 * }
5787 * }
5788 * }</pre></blockquote>
5789 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5790 * be modified by execution of the target, and so are passed unchanged
5791 * from the caller to the handler, if the handler is invoked.
5792 * <p>
5793 * The target and handler must return the same type, even if the handler
5794 * always throws. (This might happen, for instance, because the handler
5795 * is simulating a {@code finally} clause).
5796 * To create such a throwing handler, compose the handler creation logic
5797 * with {@link #throwException throwException},
5798 * in order to create a method handle of the correct return type.
5799 * @param target method handle to call
5800 * @param exType the type of exception which the handler will catch
5801 * @param handler method handle to call if a matching exception is thrown
5802 * @return method handle which incorporates the specified try/catch logic
5803 * @throws NullPointerException if any argument is null
5804 * @throws IllegalArgumentException if {@code handler} does not accept
5805 * the given exception type, or if the method handle types do
5806 * not match in their return types and their
5807 * corresponding parameters
5808 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
5809 */
5810 public static MethodHandle catchException(MethodHandle target,
5811 Class<? extends Throwable> exType,
5812 MethodHandle handler) {
5813 MethodType ttype = target.type();
5814 MethodType htype = handler.type();
5815 if (!Throwable.class.isAssignableFrom(exType))
5816 throw new ClassCastException(exType.getName());
5817 if (htype.parameterCount() < 1 ||
5818 !htype.parameterType(0).isAssignableFrom(exType))
5819 throw newIllegalArgumentException("handler does not accept exception type "+exType);
5820 if (htype.returnType() != ttype.returnType())
5821 throw misMatchedTypes("target and handler return types", ttype, htype);
5822 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
5823 if (handler == null) {
5824 throw misMatchedTypes("target and handler types", ttype, htype);
5825 }
5826 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
5827 }
5828
5829 /**
5830 * Produces a method handle which will throw exceptions of the given {@code exType}.
5831 * The method handle will accept a single argument of {@code exType},
5832 * and immediately throw it as an exception.
5833 * The method type will nominally specify a return of {@code returnType}.
5834 * The return type may be anything convenient: It doesn't matter to the
5835 * method handle's behavior, since it will never return normally.
5836 * @param returnType the return type of the desired method handle
5837 * @param exType the parameter type of the desired method handle
5838 * @return method handle which can throw the given exceptions
5839 * @throws NullPointerException if either argument is null
5840 */
5841 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
5842 if (!Throwable.class.isAssignableFrom(exType))
5843 throw new ClassCastException(exType.getName());
5844 return MethodHandleImpl.throwException(methodType(returnType, exType));
5845 }
5846
5847 /**
5848 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
5849 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
5850 * delivers the loop's result, which is the return value of the resulting handle.
5851 * <p>
5852 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
5853 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
5854 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
5855 * terms of method handles, each clause will specify up to four independent actions:<ul>
5856 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
5857 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
5858 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
5859 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
5860 * </ul>
5861 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
5862 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
5863 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
5864 * <p>
5865 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
5866 * this case. See below for a detailed description.
5867 * <p>
5868 * <em>Parameters optional everywhere:</em>
5869 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
5870 * As an exception, the init functions cannot take any {@code v} parameters,
5871 * because those values are not yet computed when the init functions are executed.
5872 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
5873 * In fact, any clause function may take no arguments at all.
5874 * <p>
5875 * <em>Loop parameters:</em>
5876 * A clause function may take all the iteration variable values it is entitled to, in which case
5877 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
5878 * with their types and values notated as {@code (A...)} and {@code (a...)}.
5879 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
5880 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
5881 * init function is automatically a loop parameter {@code a}.)
5882 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
5883 * These loop parameters act as loop-invariant values visible across the whole loop.
5884 * <p>
5885 * <em>Parameters visible everywhere:</em>
5886 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
5887 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
5888 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
5889 * Most clause functions will not need all of this information, but they will be formally connected to it
5890 * as if by {@link #dropArguments}.
5891 * <a id="astar"></a>
5892 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
5893 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
5894 * In that notation, the general form of an init function parameter list
5895 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
5896 * <p>
5897 * <em>Checking clause structure:</em>
5898 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
5899 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
5900 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
5901 * met by the inputs to the loop combinator.
5902 * <p>
5903 * <em>Effectively identical sequences:</em>
5904 * <a id="effid"></a>
5905 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
5906 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
5907 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
5908 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
5909 * that longest list.
5910 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
5911 * and the same is true if more sequences of the form {@code (V... A*)} are added.
5912 * <p>
5913 * <em>Step 0: Determine clause structure.</em><ol type="a">
5914 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
5915 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
5916 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
5917 * four. Padding takes place by appending elements to the array.
5918 * <li>Clauses with all {@code null}s are disregarded.
5919 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
5920 * </ol>
5921 * <p>
5922 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
5923 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
5924 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
5925 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
5926 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
5927 * iteration variable type.
5928 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
5929 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
5930 * </ol>
5931 * <p>
5932 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
5933 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
5934 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
5935 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
5936 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
5937 * (These types will be checked in step 2, along with all the clause function types.)
5938 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
5939 * <li>All of the collected parameter lists must be effectively identical.
5940 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
5941 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
5942 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
5943 * the "internal parameter list".
5944 * </ul>
5945 * <p>
5946 * <em>Step 1C: Determine loop return type.</em><ol type="a">
5947 * <li>Examine fini function return types, disregarding omitted fini functions.
5948 * <li>If there are no fini functions, the loop return type is {@code void}.
5949 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
5950 * type.
5951 * </ol>
5952 * <p>
5953 * <em>Step 1D: Check other types.</em><ol type="a">
5954 * <li>There must be at least one non-omitted pred function.
5955 * <li>Every non-omitted pred function must have a {@code boolean} return type.
5956 * </ol>
5957 * <p>
5958 * <em>Step 2: Determine parameter lists.</em><ol type="a">
5959 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
5960 * <li>The parameter list for init functions will be adjusted to the external parameter list.
5961 * (Note that their parameter lists are already effectively identical to this list.)
5962 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
5963 * effectively identical to the internal parameter list {@code (V... A...)}.
5964 * </ol>
5965 * <p>
5966 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
5967 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
5968 * type.
5969 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
5970 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
5971 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
5972 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
5973 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
5974 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
5975 * loop return type.
5976 * </ol>
5977 * <p>
5978 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
5979 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
5980 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
5981 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
5982 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
5983 * pad out the end of the list.
5984 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
5985 * </ol>
5986 * <p>
5987 * <em>Final observations.</em><ol type="a">
5988 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
5989 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
5990 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
5991 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
5992 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
5993 * <li>Each pair of init and step functions agrees in their return type {@code V}.
5994 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
5995 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
5996 * </ol>
5997 * <p>
5998 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
5999 * <ul>
6000 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6001 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6002 * (Only one {@code Pn} has to be non-{@code null}.)
6003 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6004 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6005 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6006 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6007 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6008 * the resulting loop handle's parameter types {@code (A...)}.
6009 * </ul>
6010 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6011 * which is natural if most of the loop computation happens in the steps. For some loops,
6012 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6013 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6014 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6015 * where the init functions will need the extra parameters. For such reasons, the rules for
6016 * determining these parameters are as symmetric as possible, across all clause parts.
6017 * In general, the loop parameters function as common invariant values across the whole
6018 * loop, while the iteration variables function as common variant values, or (if there is
6019 * no step function) as internal loop invariant temporaries.
6020 * <p>
6021 * <em>Loop execution.</em><ol type="a">
6022 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6023 * every clause function. These locals are loop invariant.
6024 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6025 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6026 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6027 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6028 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6029 * (in argument order).
6030 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6031 * returns {@code false}.
6032 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6033 * sequence {@code (v...)} of loop variables.
6034 * The updated value is immediately visible to all subsequent function calls.
6035 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6036 * (of type {@code R}) is returned from the loop as a whole.
6037 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6038 * except by throwing an exception.
6039 * </ol>
6040 * <p>
6041 * <em>Usage tips.</em>
6042 * <ul>
6043 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6044 * sometimes a step function only needs to observe the current value of its own variable.
6045 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6046 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6047 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6048 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6049 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6050 * <li>If some of the clause functions are virtual methods on an instance, the instance
6051 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6052 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6053 * will be the first iteration variable value, and it will be easy to use virtual
6054 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6055 * </ul>
6056 * <p>
6057 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6058 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6059 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6060 * <blockquote><pre>{@code
6061 * V... init...(A...);
6062 * boolean pred...(V..., A...);
6063 * V... step...(V..., A...);
6064 * R fini...(V..., A...);
6065 * R loop(A... a) {
6066 * V... v... = init...(a...);
6067 * for (;;) {
6068 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6069 * v = s(v..., a...);
6070 * if (!p(v..., a...)) {
6071 * return f(v..., a...);
6072 * }
6073 * }
6074 * }
6075 * }
6076 * }</pre></blockquote>
6077 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6078 * to their full length, even though individual clause functions may neglect to take them all.
6079 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6080 *
6081 * @apiNote Example:
6082 * <blockquote><pre>{@code
6083 * // iterative implementation of the factorial function as a loop handle
6084 * static int one(int k) { return 1; }
6085 * static int inc(int i, int acc, int k) { return i + 1; }
6086 * static int mult(int i, int acc, int k) { return i * acc; }
6087 * static boolean pred(int i, int acc, int k) { return i < k; }
6088 * static int fin(int i, int acc, int k) { return acc; }
6089 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6090 * // null initializer for counter, should initialize to 0
6091 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6092 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6093 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6094 * assertEquals(120, loop.invoke(5));
6095 * }</pre></blockquote>
6096 * The same example, dropping arguments and using combinators:
6097 * <blockquote><pre>{@code
6098 * // simplified implementation of the factorial function as a loop handle
6099 * static int inc(int i) { return i + 1; } // drop acc, k
6100 * static int mult(int i, int acc) { return i * acc; } //drop k
6101 * static boolean cmp(int i, int k) { return i < k; }
6102 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6103 * // null initializer for counter, should initialize to 0
6104 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6105 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6106 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6107 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6108 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6109 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6110 * assertEquals(720, loop.invoke(6));
6111 * }</pre></blockquote>
6112 * A similar example, using a helper object to hold a loop parameter:
6113 * <blockquote><pre>{@code
6114 * // instance-based implementation of the factorial function as a loop handle
6115 * static class FacLoop {
6116 * final int k;
6117 * FacLoop(int k) { this.k = k; }
6118 * int inc(int i) { return i + 1; }
6119 * int mult(int i, int acc) { return i * acc; }
6120 * boolean pred(int i) { return i < k; }
6121 * int fin(int i, int acc) { return acc; }
6122 * }
6123 * // assume MH_FacLoop is a handle to the constructor
6124 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6125 * // null initializer for counter, should initialize to 0
6126 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6127 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6128 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6129 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6130 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6131 * assertEquals(5040, loop.invoke(7));
6132 * }</pre></blockquote>
6133 *
6134 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6135 *
6136 * @return a method handle embodying the looping behavior as defined by the arguments.
6137 *
6138 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6139 *
6140 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6141 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6142 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6143 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6144 * @since 9
6145 */
6146 public static MethodHandle loop(MethodHandle[]... clauses) {
6147 // Step 0: determine clause structure.
6148 loopChecks0(clauses);
6149
6150 List<MethodHandle> init = new ArrayList<>();
6151 List<MethodHandle> step = new ArrayList<>();
6152 List<MethodHandle> pred = new ArrayList<>();
6153 List<MethodHandle> fini = new ArrayList<>();
6154
6155 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6156 init.add(clause[0]); // all clauses have at least length 1
6157 step.add(clause.length <= 1 ? null : clause[1]);
6158 pred.add(clause.length <= 2 ? null : clause[2]);
6159 fini.add(clause.length <= 3 ? null : clause[3]);
6160 });
6161
6162 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6163 final int nclauses = init.size();
6164
6165 // Step 1A: determine iteration variables (V...).
6166 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6167 for (int i = 0; i < nclauses; ++i) {
6168 MethodHandle in = init.get(i);
6169 MethodHandle st = step.get(i);
6170 if (in == null && st == null) {
6171 iterationVariableTypes.add(void.class);
6172 } else if (in != null && st != null) {
6173 loopChecks1a(i, in, st);
6174 iterationVariableTypes.add(in.type().returnType());
6175 } else {
6176 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6177 }
6178 }
6179 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
6180 collect(Collectors.toList());
6181
6182 // Step 1B: determine loop parameters (A...).
6183 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6184 loopChecks1b(init, commonSuffix);
6185
6186 // Step 1C: determine loop return type.
6187 // Step 1D: check other types.
6188 // local variable required here; see JDK-8223553
6189 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6190 .map(MethodType::returnType);
6191 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6192 loopChecks1cd(pred, fini, loopReturnType);
6193
6194 // Step 2: determine parameter lists.
6195 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6196 commonParameterSequence.addAll(commonSuffix);
6197 loopChecks2(step, pred, fini, commonParameterSequence);
6198
6199 // Step 3: fill in omitted functions.
6200 for (int i = 0; i < nclauses; ++i) {
6201 Class<?> t = iterationVariableTypes.get(i);
6202 if (init.get(i) == null) {
6203 init.set(i, empty(methodType(t, commonSuffix)));
6204 }
6205 if (step.get(i) == null) {
6206 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6207 }
6208 if (pred.get(i) == null) {
6209 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
6210 }
6211 if (fini.get(i) == null) {
6212 fini.set(i, empty(methodType(t, commonParameterSequence)));
6213 }
6214 }
6215
6216 // Step 4: fill in missing parameter types.
6217 // Also convert all handles to fixed-arity handles.
6218 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6219 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6220 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6221 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6222
6223 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6224 allMatch(pl -> pl.equals(commonSuffix));
6225 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6226 allMatch(pl -> pl.equals(commonParameterSequence));
6227
6228 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6229 }
6230
6231 private static void loopChecks0(MethodHandle[][] clauses) {
6232 if (clauses == null || clauses.length == 0) {
6233 throw newIllegalArgumentException("null or no clauses passed");
6234 }
6235 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6236 throw newIllegalArgumentException("null clauses are not allowed");
6237 }
6238 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6239 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6240 }
6241 }
6242
6243 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6244 if (in.type().returnType() != st.type().returnType()) {
6245 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6246 st.type().returnType());
6247 }
6248 }
6249
6250 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6251 final List<Class<?>> empty = List.of();
6252 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
6253 // take only those that can contribute to a common suffix because they are longer than the prefix
6254 map(MethodHandle::type).
6255 filter(t -> t.parameterCount() > skipSize).
6256 map(MethodType::parameterList).
6257 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6258 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
6259 }
6260
6261 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
6262 final List<Class<?>> empty = List.of();
6263 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6264 }
6265
6266 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6267 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6268 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6269 return longestParameterList(Arrays.asList(longest1, longest2));
6270 }
6271
6272 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6273 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6274 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6275 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6276 " (common suffix: " + commonSuffix + ")");
6277 }
6278 }
6279
6280 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6281 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6282 anyMatch(t -> t != loopReturnType)) {
6283 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6284 loopReturnType + ")");
6285 }
6286
6287 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
6288 throw newIllegalArgumentException("no predicate found", pred);
6289 }
6290 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6291 anyMatch(t -> t != boolean.class)) {
6292 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6293 }
6294 }
6295
6296 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6297 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6298 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6299 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6300 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6301 }
6302 }
6303
6304 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6305 return hs.stream().map(h -> {
6306 int pc = h.type().parameterCount();
6307 int tpsize = targetParams.size();
6308 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
6309 }).collect(Collectors.toList());
6310 }
6311
6312 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6313 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
6314 }
6315
6316 /**
6317 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6318 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6319 * <p>
6320 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6321 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6322 * evaluates to {@code true}).
6323 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6324 * <p>
6325 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6326 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6327 * and updated with the value returned from its invocation. The result of loop execution will be
6328 * the final value of the additional loop-local variable (if present).
6329 * <p>
6330 * The following rules hold for these argument handles:<ul>
6331 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6332 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6333 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6334 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6335 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6336 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6337 * It will constrain the parameter lists of the other loop parts.
6338 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6339 * list {@code (A...)} is called the <em>external parameter list</em>.
6340 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6341 * additional state variable of the loop.
6342 * The body must both accept and return a value of this type {@code V}.
6343 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6344 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6345 * <a href="MethodHandles.html#effid">effectively identical</a>
6346 * to the external parameter list {@code (A...)}.
6347 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6348 * {@linkplain #empty default value}.
6349 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6350 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6351 * effectively identical to the internal parameter list.
6352 * </ul>
6353 * <p>
6354 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6355 * <li>The loop handle's result type is the result type {@code V} of the body.
6356 * <li>The loop handle's parameter types are the types {@code (A...)},
6357 * from the external parameter list.
6358 * </ul>
6359 * <p>
6360 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6361 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6362 * passed to the loop.
6363 * <blockquote><pre>{@code
6364 * V init(A...);
6365 * boolean pred(V, A...);
6366 * V body(V, A...);
6367 * V whileLoop(A... a...) {
6368 * V v = init(a...);
6369 * while (pred(v, a...)) {
6370 * v = body(v, a...);
6371 * }
6372 * return v;
6373 * }
6374 * }</pre></blockquote>
6375 *
6376 * @apiNote Example:
6377 * <blockquote><pre>{@code
6378 * // implement the zip function for lists as a loop handle
6379 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6380 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6381 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6382 * zip.add(a.next());
6383 * zip.add(b.next());
6384 * return zip;
6385 * }
6386 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6387 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6388 * List<String> a = Arrays.asList("a", "b", "c", "d");
6389 * List<String> b = Arrays.asList("e", "f", "g", "h");
6390 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6391 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6392 * }</pre></blockquote>
6393 *
6394 *
6395 * @apiNote The implementation of this method can be expressed as follows:
6396 * <blockquote><pre>{@code
6397 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6398 * MethodHandle fini = (body.type().returnType() == void.class
6399 * ? null : identity(body.type().returnType()));
6400 * MethodHandle[]
6401 * checkExit = { null, null, pred, fini },
6402 * varBody = { init, body };
6403 * return loop(checkExit, varBody);
6404 * }
6405 * }</pre></blockquote>
6406 *
6407 * @param init optional initializer, providing the initial value of the loop variable.
6408 * May be {@code null}, implying a default initial value. See above for other constraints.
6409 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6410 * above for other constraints.
6411 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6412 * See above for other constraints.
6413 *
6414 * @return a method handle implementing the {@code while} loop as described by the arguments.
6415 * @throws IllegalArgumentException if the rules for the arguments are violated.
6416 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6417 *
6418 * @see #loop(MethodHandle[][])
6419 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6420 * @since 9
6421 */
6422 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6423 whileLoopChecks(init, pred, body);
6424 MethodHandle fini = identityOrVoid(body.type().returnType());
6425 MethodHandle[] checkExit = { null, null, pred, fini };
6426 MethodHandle[] varBody = { init, body };
6427 return loop(checkExit, varBody);
6428 }
6429
6430 /**
6431 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6432 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6433 * <p>
6434 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6435 * method will, in each iteration, first execute its body and then evaluate the predicate.
6436 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6437 * <p>
6438 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6439 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6440 * and updated with the value returned from its invocation. The result of loop execution will be
6441 * the final value of the additional loop-local variable (if present).
6442 * <p>
6443 * The following rules hold for these argument handles:<ul>
6444 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6445 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6446 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6447 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6448 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6449 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6450 * It will constrain the parameter lists of the other loop parts.
6451 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6452 * list {@code (A...)} is called the <em>external parameter list</em>.
6453 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6454 * additional state variable of the loop.
6455 * The body must both accept and return a value of this type {@code V}.
6456 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6457 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6458 * <a href="MethodHandles.html#effid">effectively identical</a>
6459 * to the external parameter list {@code (A...)}.
6460 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6461 * {@linkplain #empty default value}.
6462 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6463 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6464 * effectively identical to the internal parameter list.
6465 * </ul>
6466 * <p>
6467 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6468 * <li>The loop handle's result type is the result type {@code V} of the body.
6469 * <li>The loop handle's parameter types are the types {@code (A...)},
6470 * from the external parameter list.
6471 * </ul>
6472 * <p>
6473 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6474 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6475 * passed to the loop.
6476 * <blockquote><pre>{@code
6477 * V init(A...);
6478 * boolean pred(V, A...);
6479 * V body(V, A...);
6480 * V doWhileLoop(A... a...) {
6481 * V v = init(a...);
6482 * do {
6483 * v = body(v, a...);
6484 * } while (pred(v, a...));
6485 * return v;
6486 * }
6487 * }</pre></blockquote>
6488 *
6489 * @apiNote Example:
6490 * <blockquote><pre>{@code
6491 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6492 * static int zero(int limit) { return 0; }
6493 * static int step(int i, int limit) { return i + 1; }
6494 * static boolean pred(int i, int limit) { return i < limit; }
6495 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6496 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6497 * assertEquals(23, loop.invoke(23));
6498 * }</pre></blockquote>
6499 *
6500 *
6501 * @apiNote The implementation of this method can be expressed as follows:
6502 * <blockquote><pre>{@code
6503 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6504 * MethodHandle fini = (body.type().returnType() == void.class
6505 * ? null : identity(body.type().returnType()));
6506 * MethodHandle[] clause = { init, body, pred, fini };
6507 * return loop(clause);
6508 * }
6509 * }</pre></blockquote>
6510 *
6511 * @param init optional initializer, providing the initial value of the loop variable.
6512 * May be {@code null}, implying a default initial value. See above for other constraints.
6513 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6514 * See above for other constraints.
6515 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6516 * above for other constraints.
6517 *
6518 * @return a method handle implementing the {@code while} loop as described by the arguments.
6519 * @throws IllegalArgumentException if the rules for the arguments are violated.
6520 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6521 *
6522 * @see #loop(MethodHandle[][])
6523 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6524 * @since 9
6525 */
6526 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6527 whileLoopChecks(init, pred, body);
6528 MethodHandle fini = identityOrVoid(body.type().returnType());
6529 MethodHandle[] clause = {init, body, pred, fini };
6530 return loop(clause);
6531 }
6532
6533 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6534 Objects.requireNonNull(pred);
6535 Objects.requireNonNull(body);
6536 MethodType bodyType = body.type();
6537 Class<?> returnType = bodyType.returnType();
6538 List<Class<?>> innerList = bodyType.parameterList();
6539 List<Class<?>> outerList = innerList;
6540 if (returnType == void.class) {
6541 // OK
6542 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
6543 // leading V argument missing => error
6544 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6545 throw misMatchedTypes("body function", bodyType, expected);
6546 } else {
6547 outerList = innerList.subList(1, innerList.size());
6548 }
6549 MethodType predType = pred.type();
6550 if (predType.returnType() != boolean.class ||
6551 !predType.effectivelyIdenticalParameters(0, innerList)) {
6552 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6553 }
6554 if (init != null) {
6555 MethodType initType = init.type();
6556 if (initType.returnType() != returnType ||
6557 !initType.effectivelyIdenticalParameters(0, outerList)) {
6558 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6559 }
6560 }
6561 }
6562
6563 /**
6564 * Constructs a loop that runs a given number of iterations.
6565 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6566 * <p>
6567 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6568 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6569 * It will be initialized to 0 and incremented by 1 in each iteration.
6570 * <p>
6571 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6572 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6573 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6574 * <p>
6575 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6576 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6577 * iteration variable.
6578 * The result of the loop handle execution will be the final {@code V} value of that variable
6579 * (or {@code void} if there is no {@code V} variable).
6580 * <p>
6581 * The following rules hold for the argument handles:<ul>
6582 * <li>The {@code iterations} handle must not be {@code null}, and must return
6583 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6584 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6585 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6586 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6587 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6588 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6589 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6590 * of types called the <em>internal parameter list</em>.
6591 * It will constrain the parameter lists of the other loop parts.
6592 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6593 * with no additional {@code A} types, then the internal parameter list is extended by
6594 * the argument types {@code A...} of the {@code iterations} handle.
6595 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6596 * list {@code (A...)} is called the <em>external parameter list</em>.
6597 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6598 * additional state variable of the loop.
6599 * The body must both accept a leading parameter and return a value of this type {@code V}.
6600 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6601 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6602 * <a href="MethodHandles.html#effid">effectively identical</a>
6603 * to the external parameter list {@code (A...)}.
6604 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6605 * {@linkplain #empty default value}.
6606 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6607 * effectively identical to the external parameter list {@code (A...)}.
6608 * </ul>
6609 * <p>
6610 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6611 * <li>The loop handle's result type is the result type {@code V} of the body.
6612 * <li>The loop handle's parameter types are the types {@code (A...)},
6613 * from the external parameter list.
6614 * </ul>
6615 * <p>
6616 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6617 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6618 * arguments passed to the loop.
6619 * <blockquote><pre>{@code
6620 * int iterations(A...);
6621 * V init(A...);
6622 * V body(V, int, A...);
6623 * V countedLoop(A... a...) {
6624 * int end = iterations(a...);
6625 * V v = init(a...);
6626 * for (int i = 0; i < end; ++i) {
6627 * v = body(v, i, a...);
6628 * }
6629 * return v;
6630 * }
6631 * }</pre></blockquote>
6632 *
6633 * @apiNote Example with a fully conformant body method:
6634 * <blockquote><pre>{@code
6635 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6636 * // => a variation on a well known theme
6637 * static String step(String v, int counter, String init) { return "na " + v; }
6638 * // assume MH_step is a handle to the method above
6639 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6640 * MethodHandle start = MethodHandles.identity(String.class);
6641 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6642 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6643 * }</pre></blockquote>
6644 *
6645 * @apiNote Example with the simplest possible body method type,
6646 * and passing the number of iterations to the loop invocation:
6647 * <blockquote><pre>{@code
6648 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6649 * // => a variation on a well known theme
6650 * static String step(String v, int counter ) { return "na " + v; }
6651 * // assume MH_step is a handle to the method above
6652 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6653 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6654 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6655 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6656 * }</pre></blockquote>
6657 *
6658 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6659 * as loop parameters:
6660 * <blockquote><pre>{@code
6661 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6662 * // => a variation on a well known theme
6663 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6664 * // assume MH_step is a handle to the method above
6665 * MethodHandle count = MethodHandles.identity(int.class);
6666 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6667 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6668 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6669 * }</pre></blockquote>
6670 *
6671 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6672 * to enforce a loop type:
6673 * <blockquote><pre>{@code
6674 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6675 * // => a variation on a well known theme
6676 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6677 * // assume MH_step is a handle to the method above
6678 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6679 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6680 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6681 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6682 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6683 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6684 * }</pre></blockquote>
6685 *
6686 * @apiNote The implementation of this method can be expressed as follows:
6687 * <blockquote><pre>{@code
6688 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6689 * return countedLoop(empty(iterations.type()), iterations, init, body);
6690 * }
6691 * }</pre></blockquote>
6692 *
6693 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6694 * result type must be {@code int}. See above for other constraints.
6695 * @param init optional initializer, providing the initial value of the loop variable.
6696 * May be {@code null}, implying a default initial value. See above for other constraints.
6697 * @param body body of the loop, which may not be {@code null}.
6698 * It controls the loop parameters and result type in the standard case (see above for details).
6699 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6700 * and may accept any number of additional types.
6701 * See above for other constraints.
6702 *
6703 * @return a method handle representing the loop.
6704 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6705 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6706 *
6707 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6708 * @since 9
6709 */
6710 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6711 return countedLoop(empty(iterations.type()), iterations, init, body);
6712 }
6713
6714 /**
6715 * Constructs a loop that counts over a range of numbers.
6716 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6717 * <p>
6718 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
6719 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
6720 * values of the loop counter.
6721 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
6722 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
6723 * <p>
6724 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6725 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6726 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6727 * <p>
6728 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6729 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6730 * iteration variable.
6731 * The result of the loop handle execution will be the final {@code V} value of that variable
6732 * (or {@code void} if there is no {@code V} variable).
6733 * <p>
6734 * The following rules hold for the argument handles:<ul>
6735 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
6736 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
6737 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6738 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6739 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6740 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6741 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6742 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6743 * of types called the <em>internal parameter list</em>.
6744 * It will constrain the parameter lists of the other loop parts.
6745 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6746 * with no additional {@code A} types, then the internal parameter list is extended by
6747 * the argument types {@code A...} of the {@code end} handle.
6748 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6749 * list {@code (A...)} is called the <em>external parameter list</em>.
6750 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6751 * additional state variable of the loop.
6752 * The body must both accept a leading parameter and return a value of this type {@code V}.
6753 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6754 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6755 * <a href="MethodHandles.html#effid">effectively identical</a>
6756 * to the external parameter list {@code (A...)}.
6757 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6758 * {@linkplain #empty default value}.
6759 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
6760 * effectively identical to the external parameter list {@code (A...)}.
6761 * <li>Likewise, the parameter list of {@code end} must be effectively identical
6762 * to the external parameter list.
6763 * </ul>
6764 * <p>
6765 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6766 * <li>The loop handle's result type is the result type {@code V} of the body.
6767 * <li>The loop handle's parameter types are the types {@code (A...)},
6768 * from the external parameter list.
6769 * </ul>
6770 * <p>
6771 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6772 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6773 * arguments passed to the loop.
6774 * <blockquote><pre>{@code
6775 * int start(A...);
6776 * int end(A...);
6777 * V init(A...);
6778 * V body(V, int, A...);
6779 * V countedLoop(A... a...) {
6780 * int e = end(a...);
6781 * int s = start(a...);
6782 * V v = init(a...);
6783 * for (int i = s; i < e; ++i) {
6784 * v = body(v, i, a...);
6785 * }
6786 * return v;
6787 * }
6788 * }</pre></blockquote>
6789 *
6790 * @apiNote The implementation of this method can be expressed as follows:
6791 * <blockquote><pre>{@code
6792 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6793 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
6794 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
6795 * // the following semantics:
6796 * // MH_increment: (int limit, int counter) -> counter + 1
6797 * // MH_predicate: (int limit, int counter) -> counter < limit
6798 * Class<?> counterType = start.type().returnType(); // int
6799 * Class<?> returnType = body.type().returnType();
6800 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
6801 * if (returnType != void.class) { // ignore the V variable
6802 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6803 * pred = dropArguments(pred, 1, returnType); // ditto
6804 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
6805 * }
6806 * body = dropArguments(body, 0, counterType); // ignore the limit variable
6807 * MethodHandle[]
6808 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6809 * bodyClause = { init, body }, // v = init(); v = body(v, i)
6810 * indexVar = { start, incr }; // i = start(); i = i + 1
6811 * return loop(loopLimit, bodyClause, indexVar);
6812 * }
6813 * }</pre></blockquote>
6814 *
6815 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
6816 * See above for other constraints.
6817 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
6818 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
6819 * @param init optional initializer, providing the initial value of the loop variable.
6820 * May be {@code null}, implying a default initial value. See above for other constraints.
6821 * @param body body of the loop, which may not be {@code null}.
6822 * It controls the loop parameters and result type in the standard case (see above for details).
6823 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6824 * and may accept any number of additional types.
6825 * See above for other constraints.
6826 *
6827 * @return a method handle representing the loop.
6828 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
6829 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6830 *
6831 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
6832 * @since 9
6833 */
6834 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6835 countedLoopChecks(start, end, init, body);
6836 Class<?> counterType = start.type().returnType(); // int, but who's counting?
6837 Class<?> limitType = end.type().returnType(); // yes, int again
6838 Class<?> returnType = body.type().returnType();
6839 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
6840 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
6841 MethodHandle retv = null;
6842 if (returnType != void.class) {
6843 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6844 pred = dropArguments(pred, 1, returnType); // ditto
6845 retv = dropArguments(identity(returnType), 0, counterType);
6846 }
6847 body = dropArguments(body, 0, counterType); // ignore the limit variable
6848 MethodHandle[]
6849 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6850 bodyClause = { init, body }, // v = init(); v = body(v, i)
6851 indexVar = { start, incr }; // i = start(); i = i + 1
6852 return loop(loopLimit, bodyClause, indexVar);
6853 }
6854
6855 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6856 Objects.requireNonNull(start);
6857 Objects.requireNonNull(end);
6858 Objects.requireNonNull(body);
6859 Class<?> counterType = start.type().returnType();
6860 if (counterType != int.class) {
6861 MethodType expected = start.type().changeReturnType(int.class);
6862 throw misMatchedTypes("start function", start.type(), expected);
6863 } else if (end.type().returnType() != counterType) {
6864 MethodType expected = end.type().changeReturnType(counterType);
6865 throw misMatchedTypes("end function", end.type(), expected);
6866 }
6867 MethodType bodyType = body.type();
6868 Class<?> returnType = bodyType.returnType();
6869 List<Class<?>> innerList = bodyType.parameterList();
6870 // strip leading V value if present
6871 int vsize = (returnType == void.class ? 0 : 1);
6872 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
6873 // argument list has no "V" => error
6874 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6875 throw misMatchedTypes("body function", bodyType, expected);
6876 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
6877 // missing I type => error
6878 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
6879 throw misMatchedTypes("body function", bodyType, expected);
6880 }
6881 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
6882 if (outerList.isEmpty()) {
6883 // special case; take lists from end handle
6884 outerList = end.type().parameterList();
6885 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
6886 }
6887 MethodType expected = methodType(counterType, outerList);
6888 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
6889 throw misMatchedTypes("start parameter types", start.type(), expected);
6890 }
6891 if (end.type() != start.type() &&
6892 !end.type().effectivelyIdenticalParameters(0, outerList)) {
6893 throw misMatchedTypes("end parameter types", end.type(), expected);
6894 }
6895 if (init != null) {
6896 MethodType initType = init.type();
6897 if (initType.returnType() != returnType ||
6898 !initType.effectivelyIdenticalParameters(0, outerList)) {
6899 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6900 }
6901 }
6902 }
6903
6904 /**
6905 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
6906 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6907 * <p>
6908 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
6909 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
6910 * <p>
6911 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6912 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6913 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6914 * <p>
6915 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6916 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6917 * iteration variable.
6918 * The result of the loop handle execution will be the final {@code V} value of that variable
6919 * (or {@code void} if there is no {@code V} variable).
6920 * <p>
6921 * The following rules hold for the argument handles:<ul>
6922 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6923 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
6924 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6925 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
6926 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
6927 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
6928 * of types called the <em>internal parameter list</em>.
6929 * It will constrain the parameter lists of the other loop parts.
6930 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
6931 * with no additional {@code A} types, then the internal parameter list is extended by
6932 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
6933 * single type {@code Iterable} is added and constitutes the {@code A...} list.
6934 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
6935 * list {@code (A...)} is called the <em>external parameter list</em>.
6936 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6937 * additional state variable of the loop.
6938 * The body must both accept a leading parameter and return a value of this type {@code V}.
6939 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6940 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6941 * <a href="MethodHandles.html#effid">effectively identical</a>
6942 * to the external parameter list {@code (A...)}.
6943 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6944 * {@linkplain #empty default value}.
6945 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
6946 * type {@code java.util.Iterator} or a subtype thereof.
6947 * The iterator it produces when the loop is executed will be assumed
6948 * to yield values which can be converted to type {@code T}.
6949 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
6950 * effectively identical to the external parameter list {@code (A...)}.
6951 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
6952 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
6953 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
6954 * handle parameter is adjusted to accept the leading {@code A} type, as if by
6955 * the {@link MethodHandle#asType asType} conversion method.
6956 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
6957 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
6958 * </ul>
6959 * <p>
6960 * The type {@code T} may be either a primitive or reference.
6961 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
6962 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
6963 * as if by the {@link MethodHandle#asType asType} conversion method.
6964 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
6965 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
6966 * <p>
6967 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6968 * <li>The loop handle's result type is the result type {@code V} of the body.
6969 * <li>The loop handle's parameter types are the types {@code (A...)},
6970 * from the external parameter list.
6971 * </ul>
6972 * <p>
6973 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6974 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
6975 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
6976 * <blockquote><pre>{@code
6977 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
6978 * V init(A...);
6979 * V body(V,T,A...);
6980 * V iteratedLoop(A... a...) {
6981 * Iterator<T> it = iterator(a...);
6982 * V v = init(a...);
6983 * while (it.hasNext()) {
6984 * T t = it.next();
6985 * v = body(v, t, a...);
6986 * }
6987 * return v;
6988 * }
6989 * }</pre></blockquote>
6990 *
6991 * @apiNote Example:
6992 * <blockquote><pre>{@code
6993 * // get an iterator from a list
6994 * static List<String> reverseStep(List<String> r, String e) {
6995 * r.add(0, e);
6996 * return r;
6997 * }
6998 * static List<String> newArrayList() { return new ArrayList<>(); }
6999 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7000 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7001 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7002 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7003 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7004 * }</pre></blockquote>
7005 *
7006 * @apiNote The implementation of this method can be expressed approximately as follows:
7007 * <blockquote><pre>{@code
7008 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7009 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7010 * Class<?> returnType = body.type().returnType();
7011 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7012 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7013 * MethodHandle retv = null, step = body, startIter = iterator;
7014 * if (returnType != void.class) {
7015 * // the simple thing first: in (I V A...), drop the I to get V
7016 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7017 * // body type signature (V T A...), internal loop types (I V A...)
7018 * step = swapArguments(body, 0, 1); // swap V <-> T
7019 * }
7020 * if (startIter == null) startIter = MH_getIter;
7021 * MethodHandle[]
7022 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7023 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7024 * return loop(iterVar, bodyClause);
7025 * }
7026 * }</pre></blockquote>
7027 *
7028 * @param iterator an optional handle to return the iterator to start the loop.
7029 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7030 * See above for other constraints.
7031 * @param init optional initializer, providing the initial value of the loop variable.
7032 * May be {@code null}, implying a default initial value. See above for other constraints.
7033 * @param body body of the loop, which may not be {@code null}.
7034 * It controls the loop parameters and result type in the standard case (see above for details).
7035 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7036 * and may accept any number of additional types.
7037 * See above for other constraints.
7038 *
7039 * @return a method handle embodying the iteration loop functionality.
7040 * @throws NullPointerException if the {@code body} handle is {@code null}.
7041 * @throws IllegalArgumentException if any argument violates the above requirements.
7042 *
7043 * @since 9
7044 */
7045 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7046 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7047 Class<?> returnType = body.type().returnType();
7048 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7049 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7050 MethodHandle startIter;
7051 MethodHandle nextVal;
7052 {
7053 MethodType iteratorType;
7054 if (iterator == null) {
7055 // derive argument type from body, if available, else use Iterable
7056 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7057 iteratorType = startIter.type().changeParameterType(0, iterableType);
7058 } else {
7059 // force return type to the internal iterator class
7060 iteratorType = iterator.type().changeReturnType(Iterator.class);
7061 startIter = iterator;
7062 }
7063 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7064 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7065
7066 // perform the asType transforms under an exception transformer, as per spec.:
7067 try {
7068 startIter = startIter.asType(iteratorType);
7069 nextVal = nextRaw.asType(nextValType);
7070 } catch (WrongMethodTypeException ex) {
7071 throw new IllegalArgumentException(ex);
7072 }
7073 }
7074
7075 MethodHandle retv = null, step = body;
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
7083 MethodHandle[]
7084 iterVar = { startIter, null, hasNext, retv },
7085 bodyClause = { init, filterArgument(step, 0, nextVal) };
7086 return loop(iterVar, bodyClause);
7087 }
7088
7089 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7090 Objects.requireNonNull(body);
7091 MethodType bodyType = body.type();
7092 Class<?> returnType = bodyType.returnType();
7093 List<Class<?>> internalParamList = bodyType.parameterList();
7094 // strip leading V value if present
7095 int vsize = (returnType == void.class ? 0 : 1);
7096 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
7097 // argument list has no "V" => error
7098 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7099 throw misMatchedTypes("body function", bodyType, expected);
7100 } else if (internalParamList.size() <= vsize) {
7101 // missing T type => error
7102 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7103 throw misMatchedTypes("body function", bodyType, expected);
7104 }
7105 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7106 Class<?> iterableType = null;
7107 if (iterator != null) {
7108 // special case; if the body handle only declares V and T then
7109 // the external parameter list is obtained from iterator handle
7110 if (externalParamList.isEmpty()) {
7111 externalParamList = iterator.type().parameterList();
7112 }
7113 MethodType itype = iterator.type();
7114 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7115 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7116 }
7117 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7118 MethodType expected = methodType(itype.returnType(), externalParamList);
7119 throw misMatchedTypes("iterator parameters", itype, expected);
7120 }
7121 } else {
7122 if (externalParamList.isEmpty()) {
7123 // special case; if the iterator handle is null and the body handle
7124 // only declares V and T then the external parameter list consists
7125 // of Iterable
7126 externalParamList = Arrays.asList(Iterable.class);
7127 iterableType = Iterable.class;
7128 } else {
7129 // special case; if the iterator handle is null and the external
7130 // parameter list is not empty then the first parameter must be
7131 // assignable to Iterable
7132 iterableType = externalParamList.get(0);
7133 if (!Iterable.class.isAssignableFrom(iterableType)) {
7134 throw newIllegalArgumentException(
7135 "inferred first loop argument must inherit from Iterable: " + iterableType);
7136 }
7137 }
7138 }
7139 if (init != null) {
7140 MethodType initType = init.type();
7141 if (initType.returnType() != returnType ||
7142 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7143 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7144 }
7145 }
7146 return iterableType; // help the caller a bit
7147 }
7148
7149 /*non-public*/
7150 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7151 // there should be a better way to uncross my wires
7152 int arity = mh.type().parameterCount();
7153 int[] order = new int[arity];
7154 for (int k = 0; k < arity; k++) order[k] = k;
7155 order[i] = j; order[j] = i;
7156 Class<?>[] types = mh.type().parameterArray();
7157 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7158 MethodType swapType = methodType(mh.type().returnType(), types);
7159 return permuteArguments(mh, swapType, order);
7160 }
7161
7162 /**
7163 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7164 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7165 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7166 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7167 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7168 * {@code try-finally} handle.
7169 * <p>
7170 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7171 * The first is the exception thrown during the
7172 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7173 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7174 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7175 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7176 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7177 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7178 * <p>
7179 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7180 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7181 * two extra leading parameters:<ul>
7182 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7183 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7184 * the result from the execution of the {@code target} handle.
7185 * This parameter is not present if the {@code target} returns {@code void}.
7186 * </ul>
7187 * <p>
7188 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7189 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7190 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7191 * the cleanup.
7192 * <blockquote><pre>{@code
7193 * V target(A..., B...);
7194 * V cleanup(Throwable, V, A...);
7195 * V adapter(A... a, B... b) {
7196 * V result = (zero value for V);
7197 * Throwable throwable = null;
7198 * try {
7199 * result = target(a..., b...);
7200 * } catch (Throwable t) {
7201 * throwable = t;
7202 * throw t;
7203 * } finally {
7204 * result = cleanup(throwable, result, a...);
7205 * }
7206 * return result;
7207 * }
7208 * }</pre></blockquote>
7209 * <p>
7210 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7211 * be modified by execution of the target, and so are passed unchanged
7212 * from the caller to the cleanup, if it is invoked.
7213 * <p>
7214 * The target and cleanup must return the same type, even if the cleanup
7215 * always throws.
7216 * To create such a throwing cleanup, compose the cleanup logic
7217 * with {@link #throwException throwException},
7218 * in order to create a method handle of the correct return type.
7219 * <p>
7220 * Note that {@code tryFinally} never converts exceptions into normal returns.
7221 * In rare cases where exceptions must be converted in that way, first wrap
7222 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7223 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7224 * <p>
7225 * It is recommended that the first parameter type of {@code cleanup} be
7226 * declared {@code Throwable} rather than a narrower subtype. This ensures
7227 * {@code cleanup} will always be invoked with whatever exception that
7228 * {@code target} throws. Declaring a narrower type may result in a
7229 * {@code ClassCastException} being thrown by the {@code try-finally}
7230 * handle if the type of the exception thrown by {@code target} is not
7231 * assignable to the first parameter type of {@code cleanup}. Note that
7232 * various exception types of {@code VirtualMachineError},
7233 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7234 * thrown by almost any kind of Java code, and a finally clause that
7235 * catches (say) only {@code IOException} would mask any of the others
7236 * behind a {@code ClassCastException}.
7237 *
7238 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7239 * @param cleanup the handle that is invoked in the finally block.
7240 *
7241 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7242 * @throws NullPointerException if any argument is null
7243 * @throws IllegalArgumentException if {@code cleanup} does not accept
7244 * the required leading arguments, or if the method handle types do
7245 * not match in their return types and their
7246 * corresponding trailing parameters
7247 *
7248 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7249 * @since 9
7250 */
7251 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7252 List<Class<?>> targetParamTypes = target.type().parameterList();
7253 Class<?> rtype = target.type().returnType();
7254
7255 tryFinallyChecks(target, cleanup);
7256
7257 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7258 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7259 // target parameter list.
7260 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
7261
7262 // Ensure that the intrinsic type checks the instance thrown by the
7263 // target against the first parameter of cleanup
7264 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7265
7266 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7267 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7268 }
7269
7270 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7271 Class<?> rtype = target.type().returnType();
7272 if (rtype != cleanup.type().returnType()) {
7273 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7274 }
7275 MethodType cleanupType = cleanup.type();
7276 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7277 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7278 }
7279 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7280 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7281 }
7282 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7283 // target parameter list.
7284 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7285 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7286 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7287 cleanup.type(), target.type());
7288 }
7289 }
7290
7291 }