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