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