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.JavaLangAccess;
29 import jdk.internal.access.SharedSecrets;
30 import jdk.internal.module.IllegalAccessLogger;
31 import jdk.internal.org.objectweb.asm.ClassReader;
32 import jdk.internal.reflect.CallerSensitive;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.vm.annotation.ForceInline;
35 import sun.invoke.util.ValueConversions;
36 import sun.invoke.util.VerifyAccess;
37 import sun.invoke.util.Wrapper;
38 import sun.reflect.misc.ReflectUtil;
39 import sun.security.util.SecurityConstants;
40
41 import java.lang.invoke.LambdaForm.BasicType;
42 import java.lang.reflect.Constructor;
43 import java.lang.reflect.Field;
44 import java.lang.reflect.Member;
45 import java.lang.reflect.Method;
46 import java.lang.reflect.Modifier;
47 import java.lang.reflect.ReflectPermission;
48 import java.nio.ByteOrder;
49 import java.security.ProtectionDomain;
50 import java.util.ArrayList;
51 import java.util.Arrays;
52 import java.util.BitSet;
53 import java.util.Iterator;
54 import java.util.List;
55 import java.util.Objects;
56 import java.util.Set;
57 import java.util.concurrent.ConcurrentHashMap;
58 import java.util.stream.Collectors;
59 import java.util.stream.Stream;
60
61 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
62 import static java.lang.invoke.MethodHandleNatives.Constants.*;
63 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
64 import static java.lang.invoke.MethodType.methodType;
65
66 /**
67 * This class consists exclusively of static methods that operate on or return
68 * method handles. They fall into several categories:
69 * <ul>
70 * <li>Lookup methods which help create method handles for methods and fields.
71 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
72 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
73 * </ul>
74 * A lookup, combinator, or factory method will fail and throw an
75 * {@code IllegalArgumentException} if the created method handle's type
76 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
77 *
78 * @author John Rose, JSR 292 EG
79 * @since 1.7
80 */
81 public class MethodHandles {
82
83 private MethodHandles() { } // do not instantiate
84
85 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
86
87 // See IMPL_LOOKUP below.
88
89 //// Method handle creation from ordinary methods.
90
91 /**
92 * Returns a {@link Lookup lookup object} with
93 * full capabilities to emulate all supported bytecode behaviors of the caller.
94 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
95 * Factory methods on the lookup object can create
96 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
97 * for any member that the caller has access to via bytecodes,
98 * including protected and private fields and methods.
99 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
100 * Do not store it in place where untrusted code can access it.
101 * <p>
102 * This method is caller sensitive, which means that it may return different
103 * values to different callers.
104 * @return a lookup object for the caller of this method, with private access
105 */
106 @CallerSensitive
107 @ForceInline // to ensure Reflection.getCallerClass optimization
108 public static Lookup lookup() {
109 return new Lookup(Reflection.getCallerClass());
110 }
111
112 /**
113 * This reflected$lookup method is the alternate implementation of
114 * the lookup method when being invoked by reflection.
115 */
116 @CallerSensitive
117 private static Lookup reflected$lookup() {
118 Class<?> caller = Reflection.getCallerClass();
119 if (caller.getClassLoader() == null) {
120 throw newIllegalArgumentException("illegal lookupClass: "+caller);
121 }
122 return new Lookup(caller);
123 }
124
125 /**
126 * Returns a {@link Lookup lookup object} which is trusted minimally.
127 * The lookup has the {@code UNCONDITIONAL} mode.
128 * It can only be used to create method handles to public members of
129 * public classes in packages that are exported unconditionally.
130 * <p>
131 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
132 * of this lookup object will be {@link java.lang.Object}.
133 *
134 * @apiNote The use of Object is conventional, and because the lookup modes are
135 * limited, there is no special access provided to the internals of Object, its package
136 * or its module. This public lookup object or other lookup object with
137 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
138 * is not used to determine the lookup context.
139 *
140 * <p style="font-size:smaller;">
141 * <em>Discussion:</em>
142 * The lookup class can be changed to any other class {@code C} using an expression of the form
143 * {@link Lookup#in publicLookup().in(C.class)}.
144 * A public lookup object is always subject to
145 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
146 * Also, it cannot access
147 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
148 * @return a lookup object which is trusted minimally
149 *
150 * @revised 9
151 * @spec JPMS
152 */
153 public static Lookup publicLookup() {
154 return Lookup.PUBLIC_LOOKUP;
155 }
156
157 /**
158 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
159 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc"> private access</a>.
160 * The returned lookup object can provide access to classes in modules and packages,
161 * and members of those classes, outside the normal rules of Java access control,
162 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
163 * <p>
164 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
165 * allowed to do deep reflection on module {@code M2} and package of the target class
166 * if and only if all of the following conditions are {@code true}:
167 * <ul>
168 * <li>If there is a security manager, its {@code checkPermission} method is
169 * called to check {@code ReflectPermission("suppressAccessChecks")} and
170 * that must return normally.
171 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
172 * (This is because otherwise there would be no way to ensure the original lookup
173 * creator was a member of any particular module, and so any subsequent checks
174 * for readability and qualified exports would become ineffective.)
175 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
176 * (This is because an application intending to share intra-module access
177 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
178 * deep reflection to its own module.)
179 * <li>The target class must be a proper class, not a primitive or array class.
180 * (Thus, {@code M2} is well-defined.)
181 * <li>If the caller module {@code M1} differs from
182 * the target module {@code M2} then both of the following must be true:
183 * <ul>
184 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
185 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
186 * containing the target class to at least {@code M1}.</li>
187 * </ul>
188 * </ul>
189 * <p>
190 * If any of the above checks is violated, this method fails with an
191 * exception.
192 * <p>
193 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
194 * returns a {@code Lookup} on {@code targetClass} with full capabilities and
195 * {@code null} previous lookup class.
196 * <p>
197 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
198 * returns a {@code Lookup} on {@code targetClass} that records
199 * the lookup class of the caller as the new previous lookup class and
200 * drops {@code MODULE} access from the full capabilities mode.
201 *
202 * @param targetClass the target class
203 * @param caller the caller lookup object
204 * @return a lookup object for the target class, with private access
205 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
206 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
207 * @throws SecurityException if denied by the security manager
208 * @throws IllegalAccessException if any of the other access checks specified above fails
209 * @since 9
210 * @spec JPMS
211 * @see Lookup#dropLookupMode
212 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
213 */
214 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
215 if (caller.allowedModes == Lookup.TRUSTED) {
216 return new Lookup(targetClass);
217 }
218
219 SecurityManager sm = System.getSecurityManager();
220 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
221 if (targetClass.isPrimitive())
222 throw new IllegalArgumentException(targetClass + " is a primitive class");
223 if (targetClass.isArray())
224 throw new IllegalArgumentException(targetClass + " is an array class");
225 // Ensure that we can reason accurately about private and module access.
226 if ((caller.lookupModes() & Lookup.PRIVATE) == 0)
227 throw new IllegalAccessException("caller does not have PRIVATE lookup mode");
228 if ((caller.lookupModes() & Lookup.MODULE) == 0)
229 throw new IllegalAccessException("caller does not have MODULE lookup mode");
230
231 // previous lookup class is never set if it has MODULE access
232 assert caller.previousLookupClass() == null;
233
234 Class<?> callerClass = caller.lookupClass();
235 Module callerModule = callerClass.getModule(); // M1
236 Module targetModule = targetClass.getModule(); // M2
237 Class<?> newPreviousClass = null;
238 int newModes = Lookup.FULL_POWER_MODES;
239
240 if (targetModule != callerModule) {
241 if (!callerModule.canRead(targetModule))
242 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
243 if (targetModule.isNamed()) {
244 String pn = targetClass.getPackageName();
245 assert !pn.isEmpty() : "unnamed package cannot be in named module";
246 if (!targetModule.isOpen(pn, callerModule))
247 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
248 }
249
250 // M2 != M1, set previous lookup class to M1 and drop MODULE access
251 newPreviousClass = callerClass;
252 newModes &= ~Lookup.MODULE;
253 }
254
255 if (!callerModule.isNamed() && targetModule.isNamed()) {
256 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
257 if (logger != null) {
258 logger.logIfOpenedForIllegalAccess(caller, targetClass);
259 }
260 }
261 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
262 }
263
264 /**
265 * Performs an unchecked "crack" of a
266 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
267 * The result is as if the user had obtained a lookup object capable enough
268 * to crack the target method handle, called
269 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
270 * on the target to obtain its symbolic reference, and then called
271 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
272 * to resolve the symbolic reference to a member.
273 * <p>
274 * If there is a security manager, its {@code checkPermission} method
275 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
276 * @param <T> the desired type of the result, either {@link Member} or a subtype
277 * @param target a direct method handle to crack into symbolic reference components
278 * @param expected a class object representing the desired result type {@code T}
279 * @return a reference to the method, constructor, or field object
280 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
281 * @throws NullPointerException if either argument is {@code null}
282 * @throws IllegalArgumentException if the target is not a direct method handle
283 * @throws ClassCastException if the member is not of the expected type
284 * @since 1.8
285 */
286 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
287 SecurityManager smgr = System.getSecurityManager();
288 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
289 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
290 return lookup.revealDirect(target).reflectAs(expected, lookup);
291 }
292 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
293 private static final java.security.Permission ACCESS_PERMISSION =
294 new ReflectPermission("suppressAccessChecks");
295
296 /**
297 * A <em>lookup object</em> is a factory for creating method handles,
298 * when the creation requires access checking.
299 * Method handles do not perform
300 * access checks when they are called, but rather when they are created.
301 * Therefore, method handle access
302 * restrictions must be enforced when a method handle is created.
303 * The caller class against which those restrictions are enforced
304 * is known as the {@linkplain #lookupClass() lookup class}.
305 * <p>
306 * A lookup class which needs to create method handles will call
307 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
308 * When the {@code Lookup} factory object is created, the identity of the lookup class is
309 * determined, and securely stored in the {@code Lookup} object.
310 * The lookup class (or its delegates) may then use factory methods
311 * on the {@code Lookup} object to create method handles for access-checked members.
312 * This includes all methods, constructors, and fields which are allowed to the lookup class,
313 * even private ones.
314 *
315 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
316 * The factory methods on a {@code Lookup} object correspond to all major
317 * use cases for methods, constructors, and fields.
318 * Each method handle created by a factory method is the functional
319 * equivalent of a particular <em>bytecode behavior</em>.
320 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
321 * Here is a summary of the correspondence between these factory methods and
322 * the behavior of the resulting method handles:
323 * <table class="striped">
324 * <caption style="display:none">lookup method behaviors</caption>
325 * <thead>
326 * <tr>
327 * <th scope="col"><a id="equiv"></a>lookup expression</th>
328 * <th scope="col">member</th>
329 * <th scope="col">bytecode behavior</th>
330 * </tr>
331 * </thead>
332 * <tbody>
333 * <tr>
334 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
335 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
336 * </tr>
337 * <tr>
338 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
339 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
340 * </tr>
341 * <tr>
342 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
343 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
344 * </tr>
345 * <tr>
346 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
347 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
348 * </tr>
349 * <tr>
350 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
351 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
352 * </tr>
353 * <tr>
354 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
355 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
356 * </tr>
357 * <tr>
358 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
359 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
360 * </tr>
361 * <tr>
362 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
363 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
364 * </tr>
365 * <tr>
366 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
367 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
368 * </tr>
369 * <tr>
370 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
371 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
372 * </tr>
373 * <tr>
374 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
375 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
376 * </tr>
377 * <tr>
378 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
379 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
380 * </tr>
381 * <tr>
382 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
383 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
384 * </tr>
385 * <tr>
386 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
387 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
388 * </tr>
389 * </tbody>
390 * </table>
391 *
392 * Here, the type {@code C} is the class or interface being searched for a member,
393 * documented as a parameter named {@code refc} in the lookup methods.
394 * The method type {@code MT} is composed from the return type {@code T}
395 * and the sequence of argument types {@code A*}.
396 * The constructor also has a sequence of argument types {@code A*} and
397 * is deemed to return the newly-created object of type {@code C}.
398 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
399 * The formal parameter {@code this} stands for the self-reference of type {@code C};
400 * if it is present, it is always the leading argument to the method handle invocation.
401 * (In the case of some {@code protected} members, {@code this} may be
402 * restricted in type to the lookup class; see below.)
403 * The name {@code arg} stands for all the other method handle arguments.
404 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
405 * stands for a null reference if the accessed method or field is static,
406 * and {@code this} otherwise.
407 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
408 * for reflective objects corresponding to the given members declared in type {@code C}.
409 * <p>
410 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
411 * as if by {@code ldc CONSTANT_Class}.
412 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
413 * <p>
414 * In cases where the given member is of variable arity (i.e., a method or constructor)
415 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
416 * In all other cases, the returned method handle will be of fixed arity.
417 * <p style="font-size:smaller;">
418 * <em>Discussion:</em>
419 * The equivalence between looked-up method handles and underlying
420 * class members and bytecode behaviors
421 * can break down in a few ways:
422 * <ul style="font-size:smaller;">
423 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
424 * the lookup can still succeed, even when there is no equivalent
425 * Java expression or bytecoded constant.
426 * <li>Likewise, if {@code T} or {@code MT}
427 * is not symbolically accessible from the lookup class's loader,
428 * the lookup can still succeed.
429 * For example, lookups for {@code MethodHandle.invokeExact} and
430 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
431 * <li>If there is a security manager installed, it can forbid the lookup
432 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
433 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
434 * constant is not subject to security manager checks.
435 * <li>If the looked-up method has a
436 * <a href="MethodHandle.html#maxarity">very large arity</a>,
437 * the method handle creation may fail with an
438 * {@code IllegalArgumentException}, due to the method handle type having
439 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
440 * </ul>
441 *
442 * <h2><a id="access"></a>Access checking</h2>
443 * Access checks are applied in the factory methods of {@code Lookup},
444 * when a method handle is created.
445 * This is a key difference from the Core Reflection API, since
446 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
447 * performs access checking against every caller, on every call.
448 * <p>
449 * All access checks start from a {@code Lookup} object, which
450 * compares its recorded lookup class against all requests to
451 * create method handles.
452 * A single {@code Lookup} object can be used to create any number
453 * of access-checked method handles, all checked against a single
454 * lookup class.
455 * <p>
456 * A {@code Lookup} object can be shared with other trusted code,
457 * such as a metaobject protocol.
458 * A shared {@code Lookup} object delegates the capability
459 * to create method handles on private members of the lookup class.
460 * Even if privileged code uses the {@code Lookup} object,
461 * the access checking is confined to the privileges of the
462 * original lookup class.
463 * <p>
464 * A lookup can fail, because
465 * the containing class is not accessible to the lookup class, or
466 * because the desired class member is missing, or because the
467 * desired class member is not accessible to the lookup class, or
468 * because the lookup object is not trusted enough to access the member.
469 * In the case of a field setter function on a {@code final} field,
470 * finality enforcement is treated as a kind of access control,
471 * and the lookup will fail, except in special cases of
472 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
473 * In any of these cases, a {@code ReflectiveOperationException} will be
474 * thrown from the attempted lookup. The exact class will be one of
475 * the following:
476 * <ul>
477 * <li>NoSuchMethodException — if a method is requested but does not exist
478 * <li>NoSuchFieldException — if a field is requested but does not exist
479 * <li>IllegalAccessException — if the member exists but an access check fails
480 * </ul>
481 * <p>
482 * In general, the conditions under which a method handle may be
483 * looked up for a method {@code M} are no more restrictive than the conditions
484 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
485 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
486 * a method handle lookup will generally raise a corresponding
487 * checked exception, such as {@code NoSuchMethodException}.
488 * And the effect of invoking the method handle resulting from the lookup
489 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
490 * to executing the compiled, verified, and resolved call to {@code M}.
491 * The same point is true of fields and constructors.
492 * <p style="font-size:smaller;">
493 * <em>Discussion:</em>
494 * Access checks only apply to named and reflected methods,
495 * constructors, and fields.
496 * Other method handle creation methods, such as
497 * {@link MethodHandle#asType MethodHandle.asType},
498 * do not require any access checks, and are used
499 * independently of any {@code Lookup} object.
500 * <p>
501 * If the desired member is {@code protected}, the usual JVM rules apply,
502 * including the requirement that the lookup class must either be in the
503 * same package as the desired member, or must inherit that member.
504 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
505 * In addition, if the desired member is a non-static field or method
506 * in a different package, the resulting method handle may only be applied
507 * to objects of the lookup class or one of its subclasses.
508 * This requirement is enforced by narrowing the type of the leading
509 * {@code this} parameter from {@code C}
510 * (which will necessarily be a superclass of the lookup class)
511 * to the lookup class itself.
512 * <p>
513 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
514 * that the receiver argument must match both the resolved method <em>and</em>
515 * the current class. Again, this requirement is enforced by narrowing the
516 * type of the leading parameter to the resulting method handle.
517 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
518 * <p>
519 * The JVM represents constructors and static initializer blocks as internal methods
520 * with special names ({@code "<init>"} and {@code "<clinit>"}).
521 * The internal syntax of invocation instructions allows them to refer to such internal
522 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
523 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
524 * <p>
525 * If the relationship between nested types is expressed directly through the
526 * {@code NestHost} and {@code NestMembers} attributes
527 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
528 * then the associated {@code Lookup} object provides direct access to
529 * the lookup class and all of its nestmates
530 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
531 * Otherwise, access between nested classes is obtained by the Java compiler creating
532 * a wrapper method to access a private method of another class in the same nest.
533 * For example, a nested class {@code C.D}
534 * can access private members within other related classes such as
535 * {@code C}, {@code C.D.E}, or {@code C.B},
536 * but the Java compiler may need to generate wrapper methods in
537 * those related classes. In such cases, a {@code Lookup} object on
538 * {@code C.E} would be unable to access those private members.
539 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
540 * which can transform a lookup on {@code C.E} into one on any of those other
541 * classes, without special elevation of privilege.
542 * <p>
543 * The accesses permitted to a given lookup object may be limited,
544 * according to its set of {@link #lookupModes lookupModes},
545 * to a subset of members normally accessible to the lookup class.
546 * For example, the {@link MethodHandles#publicLookup publicLookup}
547 * method produces a lookup object which is only allowed to access
548 * public members in public classes of exported packages.
549 * The caller sensitive method {@link MethodHandles#lookup lookup}
550 * produces a lookup object with full capabilities relative to
551 * its caller class, to emulate all supported bytecode behaviors.
552 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
553 * with fewer access modes than the original lookup object.
554 *
555 * <p style="font-size:smaller;">
556 * <a id="privacc"></a>
557 * <em>Discussion of private access:</em>
558 * We say that a lookup has <em>private access</em>
559 * if its {@linkplain #lookupModes lookup modes}
560 * include the possibility of accessing {@code private} members
561 * (which includes the private members of nestmates).
562 * As documented in the relevant methods elsewhere,
563 * only lookups with private access possess the following capabilities:
564 * <ul style="font-size:smaller;">
565 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
566 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
567 * such as {@code Class.forName}
568 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
569 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
570 * for classes accessible to the lookup class
571 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
572 * within the same package member
573 * </ul>
574 * <p style="font-size:smaller;">
575 * Each of these permissions is a consequence of the fact that a lookup object
576 * with private access can be securely traced back to an originating class,
577 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
578 * can be reliably determined and emulated by method handles.
579 *
580 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
581 * When a lookup class in one module {@code M1} accesses a class in another module
582 * {@code M2}, extra access checking is performed beyond the access mode bits.
583 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
584 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
585 * and when the type is in a package of {@code M2} that is exported to
586 * at least {@code M1}.
587 * <p>
588 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
589 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
590 * MethodHandles.privateLookupIn} methods.
591 * Teleporting across modules will always record the original lookup class as
592 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
593 * and drops {@link Lookup#MODULE MODULE} access.
594 * If the target class is in the same module as the lookup class {@code C},
595 * then the target class becomes the new lookup class
596 * and there is no change to the previous lookup class.
597 * If the target class is in a different module from {@code M1} ({@code C}'s module),
598 * {@code C} becomes the new previous lookup class
599 * and the target class becomes the new lookup class.
600 * In that case, if there was already a previous lookup class in {@code M0},
601 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
602 * drops all privileges.
603 * For example,
604 * <blockquote><pre>
605 * {@code
606 * Lookup lookup = MethodHandles.lookup(); // in class C
607 * Lookup lookup2 = lookup.in(D.class);
608 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
609 * }</pre></blockquote>
610 * <p>
611 * The {@link #lookup()} factory method produces a {@code Lookup} object
612 * with {@code null} previous lookup class.
613 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
614 * to class {@code D} without elevation of privileges.
615 * If {@code C} and {@code D} are in the same module,
616 * {@code lookup2} records {@code D} as the new lookup class and keeps the
617 * same previous lookup class as the original {@code lookup}, or
618 * {@code null} if not present.
619 * <p>
620 * When a {@code Lookup} teleports from a class
621 * in one nest to another nest, {@code PRIVATE} access is dropped.
622 * When a {@code Lookup} teleports from a class in one package to
623 * another package, {@code PACKAGE} access is dropped.
624 * When a {@code Lookup} teleports from a class in one module to another module,
625 * {@code MODULE} access is dropped.
626 * Teleporting across modules drops the ability to access non-exported classes
627 * in both the module of the new lookup class and the module of the old lookup class
628 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
629 * A {@code Lookup} can teleport back and forth to a class in the module of
630 * the lookup class and the module of the previous class lookup.
631 * Teleporting across modules can only decrease access but cannot increase it.
632 * Teleporting to some third module drops all accesses.
633 * <p>
634 * In the above example, if {@code C} and {@code D} are in different modules,
635 * {@code lookup2} records {@code D} as its lookup class and
636 * {@code C} as its previous lookup class and {@code lookup2} has only
637 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
638 * {@code C}'s module and {@code D}'s module.
639 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
640 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
641 * class {@code D} is recorded as its previous lookup class.
642 * <p>
643 * Teleporting across modules restricts access to the public types that
644 * both the lookup class and the previous lookup class can equally access
645 * (see below).
646 * <p>
647 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
648 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
649 * and create a new {@code Lookup} with <a href="#privcc">private access</a>
650 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
651 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
652 * to call {@code privateLookupIn}.
653 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
654 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
655 * produces a new {@code Lookup} on {@code T} with full capabilities.
656 * A {@code lookup} on {@code C} is also allowed
657 * to do deep reflection on {@code T} in another module {@code M2} if
658 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
659 * the package containing {@code T} to at least {@code M1}.
660 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
661 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
662 * The resulting {@code Lookup} can be used to do member lookup or teleport
663 * to another lookup class by calling {@link #in Lookup::in}. But
664 * it cannot be used to obtain another private {@code Lookup} by calling
665 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
666 * because it has no {@code MODULE} access.
667 *
668 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
669 *
670 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
671 * allows cross-module access. The access checking is performed with respect
672 * to both the lookup class and the previous lookup class if present.
673 * <p>
674 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
675 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
676 * exported unconditionally}.
677 * <p>
678 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
679 * the lookup with {@link #PUBLIC} mode can access all public types in modules
680 * that are readable to {@code M1} and the type is in a package that is exported
681 * at least to {@code M1}.
682 * <p>
683 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
684 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
685 * the intersection of all public types that are accessible to {@code M1}
686 * with all public types that are accessible to {@code M0}. {@code M0}
687 * reads {@code M1} and hence the set of accessible types includes:
688 *
689 * <table class="striped">
690 * <caption style="display:none">
691 * Public types in the following packages are accessible to the
692 * lookup class and the previous lookup class.
693 * </caption>
694 * <thead>
695 * <tr>
696 * <th scope="col">Equally accessible types to {@code M0} and {@code M1}</th>
697 * </tr>
698 * </thead>
699 * <tbody>
700 * <tr>
701 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M1}</th>
702 * </tr>
703 * <tr>
704 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</th>
705 * </tr>
706 * <tr>
707 * <th scope="row" style="text-align:left">unconditional-exported packages from a third module {@code M2}
708 * if both {@code M0} and {@code M1} read {@code M2}</th>
709 * </tr>
710 * <tr>
711 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M1} to {@code M0}</th>
712 * </tr>
713 * <tr>
714 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M0} to {@code M1}
715 * if {@code M1} reads {@code M0}</th>
716 * </tr>
717 * <tr>
718 * <th scope="row" style="text-align:left">qualified-exported packages from a third module {@code M2} to
719 * both {@code M0} and {@code M1} if both {@code M0} and {@code M1} read {@code M2}</th>
720 * </tr>
721 * </tbody>
722 * </table>
723 *
724 * <h2><a id="access-modes"></a>Access modes</h2>
725 *
726 * The table below shows the access modes of a {@code Lookup} produced by
727 * any of the following factory or transformation methods:
728 * <ul>
729 * <li>{@link #lookup() MethodHandles.lookup()}</li>
730 * <li>{@link #publicLookup() MethodHandles.publicLookup()}</li>
731 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn}</li>
732 * <li>{@link Lookup#in}</li>
733 * <li>{@link Lookup#dropLookupMode(int)}</li>
734 * </ul>
735 *
736 * <table class="striped">
737 * <caption style="display:none">
738 * Access mode summary
739 * </caption>
740 * <thead>
741 * <tr>
742 * <th scope="col">Lookup object</th>
743 * <th style="text-align:center">protected</th>
744 * <th style="text-align:center">private</th>
745 * <th style="text-align:center">package</th>
746 * <th style="text-align:center">module</th>
747 * <th style="text-align:center">public</th>
748 * </tr>
749 * </thead>
750 * <tbody>
751 * <tr>
752 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
753 * <td style="text-align:center">PRO</td>
754 * <td style="text-align:center">PRI</td>
755 * <td style="text-align:center">PAC</td>
756 * <td style="text-align:center">MOD</td>
757 * <td style="text-align:center">1R</td>
758 * </tr>
759 * <tr>
760 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
761 * <td></td>
762 * <td></td>
763 * <td style="text-align:center">PAC</td>
764 * <td style="text-align:center">MOD</td>
765 * <td style="text-align:center">1R</td>
766 * </tr>
767 * <tr>
768 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
769 * <td></td>
770 * <td></td>
771 * <td></td>
772 * <td style="text-align:center">MOD</td>
773 * <td style="text-align:center">1R</td>
774 * </tr>
775 * <tr>
776 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
777 * <td></td>
778 * <td></td>
779 * <td></td>
780 * <td></td>
781 * <td style="text-align:center">2R</td>
782 * </tr>
783 * <tr>
784 * <td>{@code CL.in(D).in(C)} hop back to module</td>
785 * <td></td>
786 * <td></td>
787 * <td></td>
788 * <td></td>
789 * <td style="text-align:center">2R</td>
790 * </tr>
791 * <tr>
792 * <td>{@code PRI1 = privateLookupIn(C1,CL)}</td>
793 * <td style="text-align:center">PRO</td>
794 * <td style="text-align:center">PRI</td>
795 * <td style="text-align:center">PAC</td>
796 * <td style="text-align:center">MOD</td>
797 * <td style="text-align:center">1R</td>
798 * </tr>
799 * <tr>
800 * <td>{@code PRI1a = privateLookupIn(C,PRI1)}</td>
801 * <td style="text-align:center">PRO</td>
802 * <td style="text-align:center">PRI</td>
803 * <td style="text-align:center">PAC</td>
804 * <td style="text-align:center">MOD</td>
805 * <td style="text-align:center">1R</td>
806 * </tr>
807 * <tr>
808 * <td>{@code PRI1.in(C1)} same package</td>
809 * <td></td>
810 * <td></td>
811 * <td style="text-align:center">PAC</td>
812 * <td style="text-align:center">MOD</td>
813 * <td style="text-align:center">1R</td>
814 * </tr>
815 * <tr>
816 * <td>{@code PRI1.in(C1)} different package</td>
817 * <td></td>
818 * <td></td>
819 * <td></td>
820 * <td style="text-align:center">MOD</td>
821 * <td style="text-align:center">1R</td>
822 * </tr>
823 * <tr>
824 * <td>{@code PRI1.in(D)} different module</td>
825 * <td></td>
826 * <td></td>
827 * <td></td>
828 * <td></td>
829 * <td style="text-align:center">2R</td>
830 * </tr>
831 * <tr>
832 * <td>{@code PRI1.dropLookupMode(PROTECTED)}</td>
833 * <td></td>
834 * <td style="text-align:center">PRI</td>
835 * <td style="text-align:center">PAC</td>
836 * <td style="text-align:center">MOD</td>
837 * <td style="text-align:center">1R</td>
838 * </tr>
839 * <tr>
840 * <td>{@code PRI1.dropLookupMode(PRIVATE)}</td>
841 * <td></td>
842 * <td></td>
843 * <td style="text-align:center">PAC</td>
844 * <td style="text-align:center">MOD</td>
845 * <td style="text-align:center">1R</td>
846 * </tr>
847 * <tr>
848 * <td>{@code PRI1.dropLookupMode(PACKAGE)}</td>
849 * <td></td>
850 * <td></td>
851 * <td></td>
852 * <td style="text-align:center">MOD</td>
853 * <td style="text-align:center">1R</td>
854 * </tr>
855 * <tr>
856 * <td>{@code PRI1.dropLookupMode(MODULE)}</td>
857 * <td></td>
858 * <td></td>
859 * <td></td>
860 * <td></td>
861 * <td style="text-align:center">1R</td>
862 * </tr>
863 * <tr>
864 * <td>{@code PRI1.dropLookupMode(PUBLIC)}</td>
865 * <td></td>
866 * <td></td>
867 * <td></td>
868 * <td></td>
869 * <td style="text-align:center">none</td>
870 * <tr>
871 * <td>{@code PRI2 = privateLookupIn(D,CL)}</td>
872 * <td style="text-align:center">PRO</td>
873 * <td style="text-align:center">PRI</td>
874 * <td style="text-align:center">PAC</td>
875 * <td></td>
876 * <td style="text-align:center">2R</td>
877 * </tr>
878 * <tr>
879 * <td>{@code privateLookupIn(D,PRI1)}</td>
880 * <td style="text-align:center">PRO</td>
881 * <td style="text-align:center">PRI</td>
882 * <td style="text-align:center">PAC</td>
883 * <td></td>
884 * <td style="text-align:center">2R</td>
885 * </tr>
886 * <tr>
887 * <td>{@code privateLookupIn(C,PRI2)} fails</td>
888 * <td></td>
889 * <td></td>
890 * <td></td>
891 * <td></td>
892 * <td style="text-align:center">IAE</td>
893 * </tr>
894 * <tr>
895 * <td>{@code PRI2.in(D2)} same package</td>
896 * <td></td>
897 * <td></td>
898 * <td style="text-align:center">PAC</td>
899 * <td></td>
900 * <td style="text-align:center">2R</td>
901 * </tr>
902 * <tr>
903 * <td>{@code PRI2.in(D2)} different package</td>
904 * <td></td>
905 * <td></td>
906 * <td></td>
907 * <td></td>
908 * <td style="text-align:center">2R</td>
909 * </tr>
910 * <tr>
911 * <td>{@code PRI2.in(C1)} hop back to module</td>
912 * <td></td>
913 * <td></td>
914 * <td></td>
915 * <td></td>
916 * <td style="text-align:center">2R</td>
917 * </tr>
918 * <tr>
919 * <td>{@code PRI2.in(E)} hop to third module</td>
920 * <td></td>
921 * <td></td>
922 * <td></td>
923 * <td></td>
924 * <td style="text-align:center">none</td>
925 * </tr>
926 * <tr>
927 * <td>{@code PRI2.dropLookupMode(PROTECTED)}</td>
928 * <td></td>
929 * <td style="text-align:center">PRI</td>
930 * <td style="text-align:center">PAC</td>
931 * <td></td>
932 * <td style="text-align:center">2R</td>
933 * </tr>
934 * <tr>
935 * <td>{@code PRI2.dropLookupMode(PRIVATE)}</td>
936 * <td></td>
937 * <td></td>
938 * <td style="text-align:center">PAC</td>
939 * <td></td>
940 * <td style="text-align:center">2R</td>
941 * </tr>
942 * <tr>
943 * <td>{@code PRI2.dropLookupMode(PACKAGE)}</td>
944 * <td></td>
945 * <td></td>
946 * <td></td>
947 * <td></td>
948 * <td style="text-align:center">2R</td>
949 * </tr>
950 * <tr>
951 * <td>{@code PRI2.dropLookupMode(MODULE)}</td>
952 * <td></td>
953 * <td></td>
954 * <td></td>
955 * <td></td>
956 * <td style="text-align:center">2R</td>
957 * </tr>
958 * <tr>
959 * <td>{@code PRI2.dropLookupMode(PUBLIC)}</td>
960 * <td></td>
961 * <td></td>
962 * <td></td>
963 * <td></td>
964 * <td style="text-align:center">none</td>
965 * </tr>
966 * <tr>
967 * <td>{@code CL.dropLookupMode(PROTECTED)}</td>
968 * <td></td>
969 * <td style="text-align:center">PRI</td>
970 * <td style="text-align:center">PAC</td>
971 * <td style="text-align:center">MOD</td>
972 * <td style="text-align:center">1R</td>
973 * </tr>
974 * <tr>
975 * <td>{@code CL.dropLookupMode(PRIVATE)}</td>
976 * <td></td>
977 * <td></td>
978 * <td style="text-align:center">PAC</td>
979 * <td style="text-align:center">MOD</td>
980 * <td style="text-align:center">1R</td>
981 * </tr>
982 * <tr>
983 * <td>{@code CL.dropLookupMode(PACKAGE)}</td>
984 * <td></td>
985 * <td></td>
986 * <td></td>
987 * <td style="text-align:center">MOD</td>
988 * <td style="text-align:center">1R</td>
989 * </tr>
990 * <tr>
991 * <td>{@code CL.dropLookupMode(MODULE)}</td>
992 * <td></td>
993 * <td></td>
994 * <td></td>
995 * <td></td>
996 * <td style="text-align:center">1R</td>
997 * </tr>
998 * <tr>
999 * <td>{@code CL.dropLookupMode(PUBLIC)}</td>
1000 * <td></td>
1001 * <td></td>
1002 * <td></td>
1003 * <td></td>
1004 * <td style="text-align:center">none</td>
1005 * </tr>
1006 * <tr>
1007 * <td>{@code PUB = publicLookup()}</td>
1008 * <td></td>
1009 * <td></td>
1010 * <td></td>
1011 * <td></td>
1012 * <td style="text-align:center">U</td>
1013 * </tr>
1014 * <tr>
1015 * <td>{@code PUB.in(D)} different module</td>
1016 * <td></td>
1017 * <td></td>
1018 * <td></td>
1019 * <td></td>
1020 * <td style="text-align:center">U</td>
1021 * </tr>
1022 * <tr>
1023 * <td>{@code PUB.in(D).in(E)} third module</td>
1024 * <td></td>
1025 * <td></td>
1026 * <td></td>
1027 * <td></td>
1028 * <td style="text-align:center">U</td>
1029 * </tr>
1030 * <tr>
1031 * <td>{@code PUB.dropLookupMode(UNCONDITIONAL)}</td>
1032 * <td></td>
1033 * <td></td>
1034 * <td></td>
1035 * <td></td>
1036 * <td style="text-align:center">none</td>
1037 * </tr>
1038 * <tr>
1039 * <td>{@code privateLookupIn(C1,PUB)} fails</td>
1040 * <td></td>
1041 * <td></td>
1042 * <td></td>
1043 * <td></td>
1044 * <td style="text-align:center">IAE</td>
1045 * </tr>
1046 * <tr>
1047 * <td>{@code ANY.in(X)}, for inaccessible {@code X}</td>
1048 * <td></td>
1049 * <td></td>
1050 * <td></td>
1051 * <td></td>
1052 * <td style="text-align:center">none</td>
1053 * </tr>
1054 * </tbody>
1055 * </table>
1056 *
1057 * <p>
1058 * Notes:
1059 * <ul>
1060 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1061 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1062 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1063 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1064 * <li>{@code PRO} indicates {@link #PROTECTED} bit set,
1065 * {@code PRI} indicates {@link #PRIVATE} bit set,
1066 * {@code PAC} indicates {@link #PACKAGE} bit set,
1067 * {@code MOD} indicates {@link #MODULE} bit set,
1068 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1069 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1070 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1071 * <li>Public access comes in three kinds:
1072 * <ul>
1073 * <li>unconditional ({@code U}): the lookup assumes readability.
1074 * The lookup has {@code null} previous lookup class.
1075 * <li>one-module-reads ({@code 1R}): the module access checking is
1076 * performed with respect to the lookup class. The lookup has {@code null}
1077 * previous lookup class.
1078 * <li>two-module-reads ({@code 2R}): the module access checking is
1079 * performed with respect to the lookup class and the previous lookup class.
1080 * The lookup has a non-null previous lookup class which is in a
1081 * different module from the current lookup class.
1082 * </ul>
1083 * <li>Any attempt to reach a third module loses all access.</li>
1084 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1085 * all access modes are dropped.</li>
1086 * </ul>
1087 *
1088 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1089 * Although bytecode instructions can only refer to classes in
1090 * a related class loader, this API can search for methods in any
1091 * class, as long as a reference to its {@code Class} object is
1092 * available. Such cross-loader references are also possible with the
1093 * Core Reflection API, and are impossible to bytecode instructions
1094 * such as {@code invokestatic} or {@code getfield}.
1095 * There is a {@linkplain java.lang.SecurityManager security manager API}
1096 * to allow applications to check such cross-loader references.
1097 * These checks apply to both the {@code MethodHandles.Lookup} API
1098 * and the Core Reflection API
1099 * (as found on {@link java.lang.Class Class}).
1100 * <p>
1101 * If a security manager is present, member and class lookups are
1102 * subject to additional checks.
1103 * From one to three calls are made to the security manager.
1104 * Any of these calls can refuse access by throwing a
1105 * {@link java.lang.SecurityException SecurityException}.
1106 * Define {@code smgr} as the security manager,
1107 * {@code lookc} as the lookup class of the current lookup object,
1108 * {@code refc} as the containing class in which the member
1109 * is being sought, and {@code defc} as the class in which the
1110 * member is actually defined.
1111 * (If a class or other type is being accessed,
1112 * the {@code refc} and {@code defc} values are the class itself.)
1113 * The value {@code lookc} is defined as <em>not present</em>
1114 * if the current lookup object does not have
1115 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1116 * The calls are made according to the following rules:
1117 * <ul>
1118 * <li><b>Step 1:</b>
1119 * If {@code lookc} is not present, or if its class loader is not
1120 * the same as or an ancestor of the class loader of {@code refc},
1121 * then {@link SecurityManager#checkPackageAccess
1122 * smgr.checkPackageAccess(refcPkg)} is called,
1123 * where {@code refcPkg} is the package of {@code refc}.
1124 * <li><b>Step 2a:</b>
1125 * If the retrieved member is not public and
1126 * {@code lookc} is not present, then
1127 * {@link SecurityManager#checkPermission smgr.checkPermission}
1128 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1129 * <li><b>Step 2b:</b>
1130 * If the retrieved class has a {@code null} class loader,
1131 * and {@code lookc} is not present, then
1132 * {@link SecurityManager#checkPermission smgr.checkPermission}
1133 * with {@code RuntimePermission("getClassLoader")} is called.
1134 * <li><b>Step 3:</b>
1135 * If the retrieved member is not public,
1136 * and if {@code lookc} is not present,
1137 * and if {@code defc} and {@code refc} are different,
1138 * then {@link SecurityManager#checkPackageAccess
1139 * smgr.checkPackageAccess(defcPkg)} is called,
1140 * where {@code defcPkg} is the package of {@code defc}.
1141 * </ul>
1142 * Security checks are performed after other access checks have passed.
1143 * Therefore, the above rules presuppose a member or class that is public,
1144 * or else that is being accessed from a lookup class that has
1145 * rights to access the member or class.
1146 * <p>
1147 * If a security manager is present and the current lookup object does not have
1148 * <a href="MethodHandles.Lookup.html#privacc">private access</a>, then
1149 * {@link #defineClass(byte[]) defineClass} and
1150 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass}
1151 * call {@link SecurityManager#checkPermission smgr.checkPermission}
1152 * with {@code RuntimePermission("defineClass")} is called.
1153 *
1154 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1155 * A small number of Java methods have a special property called caller sensitivity.
1156 * A <em>caller-sensitive</em> method can behave differently depending on the
1157 * identity of its immediate caller.
1158 * <p>
1159 * If a method handle for a caller-sensitive method is requested,
1160 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1161 * but they take account of the lookup class in a special way.
1162 * The resulting method handle behaves as if it were called
1163 * from an instruction contained in the lookup class,
1164 * so that the caller-sensitive method detects the lookup class.
1165 * (By contrast, the invoker of the method handle is disregarded.)
1166 * Thus, in the case of caller-sensitive methods,
1167 * different lookup classes may give rise to
1168 * differently behaving method handles.
1169 * <p>
1170 * In cases where the lookup object is
1171 * {@link MethodHandles#publicLookup() publicLookup()},
1172 * or some other lookup object without
1173 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
1174 * the lookup class is disregarded.
1175 * In such cases, no caller-sensitive method handle can be created,
1176 * access is forbidden, and the lookup fails with an
1177 * {@code IllegalAccessException}.
1178 * <p style="font-size:smaller;">
1179 * <em>Discussion:</em>
1180 * For example, the caller-sensitive method
1181 * {@link java.lang.Class#forName(String) Class.forName(x)}
1182 * can return varying classes or throw varying exceptions,
1183 * depending on the class loader of the class that calls it.
1184 * A public lookup of {@code Class.forName} will fail, because
1185 * there is no reasonable way to determine its bytecode behavior.
1186 * <p style="font-size:smaller;">
1187 * If an application caches method handles for broad sharing,
1188 * it should use {@code publicLookup()} to create them.
1189 * If there is a lookup of {@code Class.forName}, it will fail,
1190 * and the application must take appropriate action in that case.
1191 * It may be that a later lookup, perhaps during the invocation of a
1192 * bootstrap method, can incorporate the specific identity
1193 * of the caller, making the method accessible.
1194 * <p style="font-size:smaller;">
1195 * The function {@code MethodHandles.lookup} is caller sensitive
1196 * so that there can be a secure foundation for lookups.
1197 * Nearly all other methods in the JSR 292 API rely on lookup
1198 * objects to check access requests.
1199 *
1200 * @revised 9
1201 */
1202 public static final
1203 class Lookup {
1204 /** The class on behalf of whom the lookup is being performed. */
1205 private final Class<?> lookupClass;
1206
1207 /** previous lookup class */
1208 private final Class<?> prevLookupClass;
1209
1210 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1211 private final int allowedModes;
1212
1213 static {
1214 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1215 }
1216
1217 /** A single-bit mask representing {@code public} access,
1218 * which may contribute to the result of {@link #lookupModes lookupModes}.
1219 * The value, {@code 0x01}, happens to be the same as the value of the
1220 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1221 * <p>
1222 * A {@code Lookup} with this lookup mode performs cross-module access check
1223 * with respect to the {@linkplain #lookupClass() lookup class} and
1224 * {@linkplain #previousLookupClass() previous lookup class} if present.
1225 */
1226 public static final int PUBLIC = Modifier.PUBLIC;
1227
1228 /** A single-bit mask representing {@code private} access,
1229 * which may contribute to the result of {@link #lookupModes lookupModes}.
1230 * The value, {@code 0x02}, happens to be the same as the value of the
1231 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1232 */
1233 public static final int PRIVATE = Modifier.PRIVATE;
1234
1235 /** A single-bit mask representing {@code protected} access,
1236 * which may contribute to the result of {@link #lookupModes lookupModes}.
1237 * The value, {@code 0x04}, happens to be the same as the value of the
1238 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1239 */
1240 public static final int PROTECTED = Modifier.PROTECTED;
1241
1242 /** A single-bit mask representing {@code package} access (default access),
1243 * which may contribute to the result of {@link #lookupModes lookupModes}.
1244 * The value is {@code 0x08}, which does not correspond meaningfully to
1245 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1246 */
1247 public static final int PACKAGE = Modifier.STATIC;
1248
1249 /** A single-bit mask representing {@code module} access,
1250 * which may contribute to the result of {@link #lookupModes lookupModes}.
1251 * The value is {@code 0x10}, which does not correspond meaningfully to
1252 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1253 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1254 * with this lookup mode can access all public types in the module of the
1255 * lookup class and public types in packages exported by other modules
1256 * to the module of the lookup class.
1257 * <p>
1258 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1259 * previous lookup class} is always {@code null}.
1260 *
1261 * @since 9
1262 * @spec JPMS
1263 */
1264 public static final int MODULE = PACKAGE << 1;
1265
1266 /** A single-bit mask representing {@code unconditional} access
1267 * which may contribute to the result of {@link #lookupModes lookupModes}.
1268 * The value is {@code 0x20}, which does not correspond meaningfully to
1269 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1270 * A {@code Lookup} with this lookup mode assumes {@linkplain
1271 * java.lang.Module#canRead(java.lang.Module) readability}.
1272 * This lookup mode can access all public members of public types
1273 * of all modules when the type is in a package that is {@link
1274 * java.lang.Module#isExported(String) exported unconditionally}.
1275 *
1276 * <p>
1277 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1278 * previous lookup class} is always {@code null}.
1279 *
1280 * @since 9
1281 * @spec JPMS
1282 * @see #publicLookup()
1283 */
1284 public static final int UNCONDITIONAL = PACKAGE << 2;
1285
1286 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
1287 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
1288 private static final int TRUSTED = -1;
1289
1290 /*
1291 * Adjust PUBLIC => PUBLIC|MODULE|UNCONDITIONAL
1292 * Adjust 0 => PACKAGE
1293 */
1294 private static int fixmods(int mods) {
1295 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
1296 if (Modifier.isPublic(mods))
1297 mods |= UNCONDITIONAL;
1298 return (mods != 0) ? mods : PACKAGE;
1299 }
1300
1301 /** Tells which class is performing the lookup. It is this class against
1302 * which checks are performed for visibility and access permissions.
1303 * <p>
1304 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1305 * access checks are performed against both the lookup class and the previous lookup class.
1306 * <p>
1307 * The class implies a maximum level of access permission,
1308 * but the permissions may be additionally limited by the bitmask
1309 * {@link #lookupModes lookupModes}, which controls whether non-public members
1310 * can be accessed.
1311 * @return the lookup class, on behalf of which this lookup object finds members
1312 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1313 */
1314 public Class<?> lookupClass() {
1315 return lookupClass;
1316 }
1317
1318 /** Reports a lookup class in another module that this lookup object
1319 * was previously teleported from, or {@code null}.
1320 * <p>
1321 * A {@code Lookup} object produced by the factory methods, such as the
1322 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1323 * has {@code null} previous lookup class.
1324 * A {@code Lookup} object has a non-null previous lookup class
1325 * when this lookup was teleported from an old lookup class
1326 * in one module to a new lookup class in another module.
1327 *
1328 * @return the lookup class in another module that this lookup object was
1329 * previously teleported from, or {@code null}
1330 * @since 14
1331 * @see #in(Class)
1332 * @see MethodHandles#privateLookupIn(Class, Lookup)
1333 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1334 */
1335 public Class<?> previousLookupClass() {
1336 return prevLookupClass;
1337 }
1338
1339 // This is just for calling out to MethodHandleImpl.
1340 private Class<?> lookupClassOrNull() {
1341 if (allowedModes == TRUSTED) {
1342 return null;
1343 }
1344 if (allowedModes == UNCONDITIONAL) {
1345 // use Object as the caller to pass to VM doing resolution
1346 return Object.class;
1347 }
1348 return lookupClass;
1349 }
1350
1351 /** Tells which access-protection classes of members this lookup object can produce.
1352 * The result is a bit-mask of the bits
1353 * {@linkplain #PUBLIC PUBLIC (0x01)},
1354 * {@linkplain #PRIVATE PRIVATE (0x02)},
1355 * {@linkplain #PROTECTED PROTECTED (0x04)},
1356 * {@linkplain #PACKAGE PACKAGE (0x08)},
1357 * {@linkplain #MODULE MODULE (0x10)},
1358 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
1359 * <p>
1360 * A freshly-created lookup object
1361 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1362 * all possible bits set, except {@code UNCONDITIONAL}.
1363 * A lookup object on a new lookup class
1364 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1365 * may have some mode bits set to zero.
1366 * Mode bits can also be
1367 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1368 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1369 * The purpose of this is to restrict access via the new lookup object,
1370 * so that it can access only names which can be reached by the original
1371 * lookup object, and also by the new lookup class.
1372 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1373 * @see #in
1374 * @see #dropLookupMode
1375 *
1376 * @revised 9
1377 * @spec JPMS
1378 */
1379 public int lookupModes() {
1380 return allowedModes & ALL_MODES;
1381 }
1382
1383 /** Embody the current class (the lookupClass) as a lookup class
1384 * for method handle creation.
1385 * Must be called by from a method in this package,
1386 * which in turn is called by a method not in this package.
1387 */
1388 Lookup(Class<?> lookupClass) {
1389 this(lookupClass, null, FULL_POWER_MODES);
1390 }
1391
1392 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1393 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1394 && prevLookupClass.getModule() != lookupClass.getModule());
1395 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1396 this.lookupClass = lookupClass;
1397 this.prevLookupClass = prevLookupClass;
1398 this.allowedModes = allowedModes;
1399 assert !lookupClass.isPrimitive() && !lookupClass.isArray();
1400 }
1401
1402 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1403 // make sure we haven't accidentally picked up a privileged class:
1404 checkUnprivilegedlookupClass(lookupClass);
1405 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1406 }
1407
1408 /**
1409 * Creates a lookup on the specified new lookup class.
1410 * The resulting object will report the specified
1411 * class as its own {@link #lookupClass() lookupClass}.
1412 *
1413 * <p>
1414 * However, the resulting {@code Lookup} object is guaranteed
1415 * to have no more access capabilities than the original.
1416 * In particular, access capabilities can be lost as follows:<ul>
1417 * <li>If the new lookup class is in a different module from the old one,
1418 * i.e. {@link #MODULE MODULE} access is lost.
1419 * <li>If the new lookup class is in a different package
1420 * than the old one, protected and default (package) members will not be accessible,
1421 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1422 * <li>If the new lookup class is not within the same package member
1423 * as the old one, private members will not be accessible, and protected members
1424 * will not be accessible by virtue of inheritance,
1425 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1426 * (Protected members may continue to be accessible because of package sharing.)
1427 * <li>If the new lookup class is not
1428 * {@linkplain #accessClass(Class) accessible} to this lookup,
1429 * then no members, not even public members, will be accessible
1430 * i.e. all access modes are lost.
1431 * <li>If the new lookup class, the old lookup class and the previous lookup class
1432 * are all in different modules i.e. teleporting to a third module,
1433 * all access modes are lost.
1434 * </ul>
1435 * <p>
1436 * The new previous lookup class is chosen as follows:
1437 * <ul>
1438 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1439 * the new previous lookup class is {@code null}.
1440 * <li>If the new lookup class is in the same module as the old lookup class,
1441 * the new previous lookup class is the old previous lookup class.
1442 * <li>If the new lookup class is in a different module from the old lookup class,
1443 * the new previous lookup class is the the old lookup class.
1444 *</ul>
1445 * <p>
1446 * The resulting lookup's capabilities for loading classes
1447 * (used during {@link #findClass} invocations)
1448 * are determined by the lookup class' loader,
1449 * which may change due to this operation.
1450 * <p>
1451 * @param requestedLookupClass the desired lookup class for the new lookup object
1452 * @return a lookup object which reports the desired lookup class, or the same object
1453 * if there is no change
1454 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1455 * @throws NullPointerException if the argument is null
1456 *
1457 * @revised 9
1458 * @spec JPMS
1459 * @see #accessClass(Class)
1460 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1461 */
1462 public Lookup in(Class<?> requestedLookupClass) {
1463 Objects.requireNonNull(requestedLookupClass);
1464 if (requestedLookupClass.isPrimitive())
1465 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1466 if (requestedLookupClass.isArray())
1467 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1468
1469 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1470 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1471 if (requestedLookupClass == this.lookupClass)
1472 return this; // keep same capabilities
1473 int newModes = (allowedModes & FULL_POWER_MODES);
1474 Module fromModule = this.lookupClass.getModule();
1475 Module targetModule = requestedLookupClass.getModule();
1476 Class<?> plc = this.previousLookupClass();
1477 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1478 assert plc == null;
1479 newModes = UNCONDITIONAL;
1480 } else if (fromModule != targetModule) {
1481 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1482 // allow hopping back and forth between fromModule and plc's module
1483 // but not the third module
1484 newModes = 0;
1485 }
1486 // drop MODULE access
1487 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1488 // teleport from this lookup class
1489 plc = this.lookupClass;
1490 }
1491 if ((newModes & PACKAGE) != 0
1492 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1493 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1494 }
1495 // Allow nestmate lookups to be created without special privilege:
1496 if ((newModes & PRIVATE) != 0
1497 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1498 newModes &= ~(PRIVATE|PROTECTED);
1499 }
1500 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1501 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1502 // The requested class it not accessible from the lookup class.
1503 // No permissions.
1504 newModes = 0;
1505 }
1506 return newLookup(requestedLookupClass, plc, newModes);
1507 }
1508
1509 /**
1510 * Creates a lookup on the same lookup class which this lookup object
1511 * finds members, but with a lookup mode that has lost the given lookup mode.
1512 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1513 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
1514 * {@link #PROTECTED PROTECTED} is always dropped and
1515 * so the resulting lookup mode will never have this access capability.
1516 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
1517 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
1518 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
1519 * is dropped then the resulting lookup has no access. If {@code UNCONDITIONAL}
1520 * is dropped then the resulting lookup has no access.
1521 *
1522 * @apiNote
1523 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1524 * delegate non-public access within the package of the lookup class without
1525 * conferring private access. A lookup with {@code MODULE} but not
1526 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1527 * the module of the lookup class without conferring package access.
1528 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1529 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1530 * to public classes accessible to both the module of the lookup class
1531 * and the module of the previous lookup class.
1532 *
1533 * @param modeToDrop the lookup mode to drop
1534 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1535 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1536 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
1537 * @see MethodHandles#privateLookupIn
1538 * @since 9
1539 */
1540 public Lookup dropLookupMode(int modeToDrop) {
1541 int oldModes = lookupModes();
1542 int newModes = oldModes & ~(modeToDrop | PROTECTED);
1543 switch (modeToDrop) {
1544 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1545 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1546 case PACKAGE: newModes &= ~(PRIVATE); break;
1547 case PROTECTED:
1548 case PRIVATE:
1549 case UNCONDITIONAL: break;
1550 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1551 }
1552 if (newModes == oldModes) return this; // return self if no change
1553 return newLookup(lookupClass(), previousLookupClass(), newModes);
1554 }
1555
1556 /**
1557 * Defines a class to the same class loader and in the same runtime package and
1558 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1559 * {@linkplain #lookupClass() lookup class}.
1560 *
1561 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1562 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1563 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1564 * that the lookup object was created by a caller in the runtime package (or derived
1565 * from a lookup originally created by suitably privileged code to a target class in
1566 * the runtime package). </p>
1567 *
1568 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1569 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1570 * same package as the lookup class. </p>
1571 *
1572 * <p> This method does not run the class initializer. The class initializer may
1573 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1574 * Specification</em>. </p>
1575 *
1576 * <p> If there is a security manager, its {@code checkPermission} method is first called
1577 * to check {@code RuntimePermission("defineClass")}. </p>
1578 *
1579 * @param bytes the class bytes
1580 * @return the {@code Class} object for the class
1581 * @throws IllegalArgumentException the bytes are for a class in a different package
1582 * to the lookup class
1583 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1584 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1585 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
1586 * @throws SecurityException if denied by the security manager
1587 * @throws NullPointerException if {@code bytes} is {@code null}
1588 * @since 9
1589 * @spec JPMS
1590 * @see Lookup#privateLookupIn
1591 * @see Lookup#dropLookupMode
1592 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1593 */
1594 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1595 SecurityManager sm = System.getSecurityManager();
1596 if (sm != null)
1597 sm.checkPermission(new RuntimePermission("defineClass"));
1598 if ((lookupModes() & PACKAGE) == 0)
1599 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1600 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
1601 return makeClassDefiner(bytes.clone()).defineClass(false);
1602 }
1603
1604 private void checkDefineClassPermission() {
1605 SecurityManager sm = System.getSecurityManager();
1606 if (sm == null) return;
1607 if (allowedModes == TRUSTED) return;
1608
1609 if (!hasPrivateAccess()) {
1610 sm.checkPermission(new RuntimePermission("defineClass"));
1611 }
1612 }
1613
1614 /**
1615 * Creates a {@code Lookup} on a <em>hidden class</em> defined to
1616 * the same class loader and in the same runtime package and
1617 * {@linkplain java.security.ProtectionDomain protection domain} as this
1618 * lookup's {@linkplain #lookupClass() lookup class}.
1619 *
1620 * If {@code options} has {@link ClassOption#NESTMATE NESTMATE} class
1621 * option, then the hidden class is added as a member into
1622 * {@linkplain Class#getNestHost() the nest} of this lookup's lookup class.
1623 *
1624 * If {@code options} has {@link ClassOption#WEAK WEAK}, then
1625 * the hidden class is weakly referenced from its defining class loader
1626 * and may be unloaded while its defining class loader is strongly reachable.
1627 *
1628 * The hidden class is initialized if the {@code initialize} parameter is
1629 * {@code true}.
1630 *
1631 * <p> A {@link Class#isHiddenClass() <em>hidden</em>} class has the
1632 * following additional properties:
1633 * <ul>
1634 * <li>Naming:
1635 * The name of a hidden class returned by {@link Class#getName()} is
1636 * defined by the JVM of this form:
1637 * {@code <fully-qualified binary name> + '/' + <suffix>}<br>
1638 * where {@code <fully-qualified binary name>} is the class name
1639 * from the class bytes and {@code <suffix>} must be an unique unqualified
1640 * name (see JVMS 4.2.2)
1641 * <li>Class resolution:
1642 * A hidden class cannot be referenced in other classes and cannot be
1643 * named as a field type, a method parameter type and a method return type.
1644 * It is not discoverable by its class loader for example via
1645 * {@link Class#forName(String, boolean, ClassLoader)},
1646 * {@link ClassLoader#loadClass(String, boolean)} and also bytecode linkage.
1647 * <li>Class retransformation:
1648 * A hidden class is not {@linkplain java.lang.instrument.Instrumentation#isModifiableClass(Class)
1649 * modifiable} by Java agents or tool agents using
1650 * the <a href="{@docRoot}/../specs/jvmti.html">JVM Tool Interface</a>.
1651 * <li>Serialization:
1652 * The default serialization mechanism records the name of a class in
1653 * its serialized form and finds the class by name during deserialization.
1654 * A <em>serializable</em> hidden class requires a custom serialization
1655 * mechanism in order to ensure that instances are properly serialized
1656 * and deserialized.
1657 * </ul>
1658 *
1659 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must
1660 * have {@code PRIVATE} and {@code MODULE} access to create a hidden class
1661 * in the module of this lookup class.
1662 *
1663 * <p> The {@code bytes} parameter is the class bytes of a valid class file
1664 * (as defined by the <em>The Java Virtual Machine Specification</em>)
1665 * with a class name in the same package as the lookup class.
1666 *
1667 * @param bytes the class bytes
1668 * @param initialize if {@code true} the class will be initialized.
1669 * @param options {@linkplain ClassOption class options}
1670 * @return the {@code Lookup} object on the hidden class
1671 *
1672 * @throws IllegalArgumentException the bytes are for a class in a different package
1673 * to the lookup class
1674 * @throws IllegalAccessException if this lookup does not have {@code PRIVATE} and {@code MODULE} access
1675 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1676 * verified ({@code VerifyError}), is already defined,
1677 * or another linkage error occurs
1678 * @throws SecurityException if a security manager is present and it
1679 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1680 * @throws NullPointerException if {@code bytes} is {@code null}
1681 *
1682 * @since 14
1683 * @see Class#isHiddenClass()
1684 * @jvms 4.2.2 Unqualified Names
1685 * @jls 12.3 Linking of Classes and Interfaces
1686 * @jls 12.4 Initialization of Classes and Interfaces
1687 */
1688 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
1689 throws IllegalAccessException
1690 {
1691 Objects.requireNonNull(bytes);
1692
1693 checkDefineClassPermission();
1694 if ((lookupModes() & (PRIVATE|MODULE)) != (PRIVATE|MODULE)){
1695 throw new IllegalAccessException(this + " does not have PRIVATE or MODULE access");
1696 }
1697
1698 Set<ClassOption> opts = (options != null && options.length > 0) ? Set.of(options) : Set.of();
1699 Class<?> c = makeHiddenClassDefiner(bytes.clone(), opts).defineClass(initialize, null);
1700 return new Lookup(c, null, FULL_POWER_MODES);
1701 }
1702
1703 /**
1704 * Creates a {@code Lookup} on a <em>hidden class</em> with {@code classData}
1705 * defined to the same class loader and in the same runtime package
1706 * and {@linkplain java.security.ProtectionDomain protection domain} as
1707 * this lookup's {@linkplain #lookupClass() lookup class} with
1708 * the given class options.
1709 *
1710 * <p> This method is equivalent to calling
1711 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
1712 * as if the hidden class has a private static final unnamed field
1713 * pre-initialized with the given {@code classData}.
1714 * The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData} method
1715 * can be used to retrieve the {@code classData}.
1716 *
1717 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must
1718 * have {@code PRIVATE} and {@code MODULE} access in order to create a
1719 * hidden class in the module of this lookup class.
1720 *
1721 * @param bytes the class bytes
1722 * @param classData pre-initialized class data
1723 * @param initialize if {@code true} the class will be initialized.
1724 * @param options {@linkplain ClassOption class options}
1725 * @return the {@code Lookup} object on the hidden class
1726 *
1727 * @throws IllegalArgumentException the bytes are for a class in a different package
1728 * to the lookup class
1729 * @throws IllegalAccessException if this lookup does not have {@code PRIVATE} and {@code MODULE} access
1730 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1731 * verified ({@code VerifyError}), is already defined,
1732 * or another linkage error occurs
1733 * @throws SecurityException if a security manager is present and it
1734 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1735 * @throws NullPointerException if {@code bytes} is {@code null}
1736 *
1737 * @since 14
1738 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1739 * @see Class#isHiddenClass()
1740 */
1741 /* package-private */ Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
1742 throws IllegalAccessException
1743 {
1744 Objects.requireNonNull(bytes);
1745 Objects.requireNonNull(classData);
1746
1747 checkDefineClassPermission();
1748 if ((lookupModes() & (PRIVATE|MODULE)) != (PRIVATE|MODULE)){
1749 throw new IllegalAccessException(this + " does not have PRIVATE or MODULE access");
1750 }
1751
1752 Set<ClassOption> opts = (options != null && options.length > 0) ? Set.of(options) : Set.of();
1753 Class<?> c = makeHiddenClassDefiner(bytes.clone(), opts).defineClass(initialize, classData);
1754 return new Lookup(c, null, FULL_POWER_MODES);
1755 }
1756
1757 private ClassDefiner makeClassDefiner(byte[] bytes) {
1758 return new ClassDefiner(this, bytes, Set.of(), 0);
1759 }
1760
1761 /**
1762 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
1763 * from the given bytes and options.
1764 *
1765 * @param bytes class bytes
1766 * @param options class options
1767 * @return ClassDefiner that defines a hidden class of the given bytes and options
1768 */
1769 ClassDefiner makeHiddenClassDefiner(byte[] bytes, Set<ClassOption> options) {
1770 return new ClassDefiner(this, bytes, options, HIDDEN_CLASS);
1771 }
1772
1773 /**
1774 * This method is only called by MethodHandleImpl.BindCaller.makeInjectedInvoker.
1775 *
1776 * @param name the name of the class and the name in the class bytes is ignored.
1777 * @param bytes class bytes
1778 * @return ClassDefiner that defines a hidden class of the given bytes
1779 */
1780 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes) {
1781 return new ClassDefiner(this, name, bytes, HIDDEN_CLASS);
1782 }
1783
1784 static class ClassDefiner {
1785 private final Lookup lookup;
1786 private final String name;
1787 private final byte[] bytes;
1788 private final int classFlags;
1789
1790 // caller should make a defensive copy of the arguments if needed
1791 // before calling this constructor
1792 private ClassDefiner(Lookup lookup, byte[] bytes, Set<ClassOption> options, int flags) {
1793 this.lookup = lookup;
1794 this.bytes = bytes;
1795 this.classFlags = flags | ClassOption.optionsToFlag(options);
1796 this.name = className(bytes);
1797
1798 int index = name.lastIndexOf('.');
1799 String pn = (index == -1) ? "" : name.substring(0, index);
1800 if (!pn.equals(lookup.lookupClass().getPackageName())) {
1801 throw newIllegalArgumentException(name + " not in same package as lookup class: " +
1802 lookup.lookupClass().getName());
1803 }
1804 }
1805
1806 // skip package name check
1807 private ClassDefiner(Lookup lookup, String name, byte[] bytes, int flags) {
1808 this.lookup = lookup;
1809 this.bytes = bytes;
1810 this.classFlags = flags;
1811 this.name = name;
1812 }
1813
1814 String className() {
1815 return name;
1816 }
1817
1818 Class<?> defineClass(boolean initialize) {
1819 return defineClass(initialize, null);
1820 }
1821
1822 /**
1823 * Defines the class of the given bytes and the given classData.
1824 * If {@code initialize} parameter is true, then the class will be initialized.
1825 *
1826 * @param initialize true if the class to be initialized
1827 * @param classData classData or null
1828 * @return the class
1829 *
1830 * @throws LinkageError linkage error
1831 */
1832 Class<?> defineClass(boolean initialize, Object classData) {
1833 Class<?> lookupClass = lookup.lookupClass();
1834 ClassLoader loader = lookupClass.getClassLoader();
1835 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
1836 Class<?> c = JLA.defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
1837 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
1838 return c;
1839 }
1840
1841 private boolean isNestmate() {
1842 return (classFlags & NESTMATE_CLASS) != 0;
1843 }
1844
1845 private static String className(byte[] bytes) {
1846 try {
1847 ClassReader reader = new ClassReader(bytes);
1848 String name = reader.getClassName();
1849 return name.replace('/', '.');
1850 } catch (IllegalArgumentException e) {
1851 throw e;
1852 } catch (RuntimeException e) {
1853 // ASM exceptions are poorly specified
1854 ClassFormatError cfe = new ClassFormatError();
1855 cfe.initCause(e);
1856 throw cfe;
1857 }
1858 }
1859 }
1860
1861 private ProtectionDomain lookupClassProtectionDomain() {
1862 ProtectionDomain pd = cachedProtectionDomain;
1863 if (pd == null) {
1864 cachedProtectionDomain = pd = JLA.protectionDomain(lookupClass);
1865 }
1866 return pd;
1867 }
1868
1869 // cached protection domain
1870 private volatile ProtectionDomain cachedProtectionDomain;
1871
1872 // Make sure outer class is initialized first.
1873 static { IMPL_NAMES.getClass(); }
1874
1875 /** Package-private version of lookup which is trusted. */
1876 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
1877
1878 /** Version of lookup which is trusted minimally.
1879 * It can only be used to create method handles to publicly accessible
1880 * members in packages that are exported unconditionally.
1881 */
1882 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
1883
1884 static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
1885
1886 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1887 String name = lookupClass.getName();
1888 if (name.startsWith("java.lang.invoke."))
1889 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1890 }
1891
1892 /**
1893 * Displays the name of the class from which lookups are to be made.
1894 * followed with "/" and the name of the {@linkplain #previousLookupClass()
1895 * previous lookup class} if present.
1896 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1897 * If there are restrictions on the access permitted to this lookup,
1898 * this is indicated by adding a suffix to the class name, consisting
1899 * of a slash and a keyword. The keyword represents the strongest
1900 * allowed access, and is chosen as follows:
1901 * <ul>
1902 * <li>If no access is allowed, the suffix is "/noaccess".
1903 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
1904 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1905 * <li>If only public and module access are allowed, the suffix is "/module".
1906 * <li>If public and package access are allowed, the suffix is "/package".
1907 * <li>If public, package, and private access are allowed, the suffix is "/private".
1908 * </ul>
1909 * If none of the above cases apply, it is the case that full access
1910 * (public, module, package, private, and protected) is allowed.
1911 * In this case, no suffix is added.
1912 * This is true only of an object obtained originally from
1913 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1914 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1915 * always have restricted access, and will display a suffix.
1916 * <p>
1917 * (It may seem strange that protected access should be
1918 * stronger than private access. Viewed independently from
1919 * package access, protected access is the first to be lost,
1920 * because it requires a direct subclass relationship between
1921 * caller and callee.)
1922 * @see #in
1923 *
1924 * @revised 9
1925 * @spec JPMS
1926 */
1927 @Override
1928 public String toString() {
1929 String cname = lookupClass.getName();
1930 if (prevLookupClass != null)
1931 cname += "/" + prevLookupClass.getName();
1932 switch (allowedModes) {
1933 case 0: // no privileges
1934 return cname + "/noaccess";
1935 case UNCONDITIONAL:
1936 return cname + "/publicLookup";
1937 case PUBLIC:
1938 return cname + "/public";
1939 case PUBLIC|MODULE:
1940 return cname + "/module";
1941 case PUBLIC|PACKAGE:
1942 case PUBLIC|MODULE|PACKAGE:
1943 return cname + "/package";
1944 case PUBLIC|PACKAGE|PRIVATE:
1945 case PUBLIC|MODULE|PACKAGE|PRIVATE:
1946 return cname + "/private";
1947 case FULL_POWER_MODES:
1948 case FULL_POWER_MODES & ~(MODULE):
1949 return cname;
1950 case TRUSTED:
1951 return "/trusted"; // internal only; not exported
1952 default: // Should not happen, but it's a bitfield...
1953 cname = cname + "/" + Integer.toHexString(allowedModes);
1954 assert(false) : cname;
1955 return cname;
1956 }
1957 }
1958
1959 /**
1960 * Produces a method handle for a static method.
1961 * The type of the method handle will be that of the method.
1962 * (Since static methods do not take receivers, there is no
1963 * additional receiver argument inserted into the method handle type,
1964 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1965 * The method and all its argument types must be accessible to the lookup object.
1966 * <p>
1967 * The returned method handle will have
1968 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1969 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1970 * <p>
1971 * If the returned method handle is invoked, the method's class will
1972 * be initialized, if it has not already been initialized.
1973 * <p><b>Example:</b>
1974 * <blockquote><pre>{@code
1975 import static java.lang.invoke.MethodHandles.*;
1976 import static java.lang.invoke.MethodType.*;
1977 ...
1978 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1979 "asList", methodType(List.class, Object[].class));
1980 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1981 * }</pre></blockquote>
1982 * @param refc the class from which the method is accessed
1983 * @param name the name of the method
1984 * @param type the type of the method
1985 * @return the desired method handle
1986 * @throws NoSuchMethodException if the method does not exist
1987 * @throws IllegalAccessException if access checking fails,
1988 * or if the method is not {@code static},
1989 * or if the method's variable arity modifier bit
1990 * is set and {@code asVarargsCollector} fails
1991 * @throws SecurityException if a security manager is present and it
1992 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1993 * @throws NullPointerException if any argument is null
1994 */
1995 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1996 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1997 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1998 }
1999
2000 /**
2001 * Produces a method handle for a virtual method.
2002 * The type of the method handle will be that of the method,
2003 * with the receiver type (usually {@code refc}) prepended.
2004 * The method and all its argument types must be accessible to the lookup object.
2005 * <p>
2006 * When called, the handle will treat the first argument as a receiver
2007 * and, for non-private methods, dispatch on the receiver's type to determine which method
2008 * implementation to enter.
2009 * For private methods the named method in {@code refc} will be invoked on the receiver.
2010 * (The dispatching action is identical with that performed by an
2011 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2012 * <p>
2013 * The first argument will be of type {@code refc} if the lookup
2014 * class has full privileges to access the member. Otherwise
2015 * the member must be {@code protected} and the first argument
2016 * will be restricted in type to the lookup class.
2017 * <p>
2018 * The returned method handle will have
2019 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2020 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2021 * <p>
2022 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2023 * instructions and method handles produced by {@code findVirtual},
2024 * if the class is {@code MethodHandle} and the name string is
2025 * {@code invokeExact} or {@code invoke}, the resulting
2026 * method handle is equivalent to one produced by
2027 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2028 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2029 * with the same {@code type} argument.
2030 * <p>
2031 * If the class is {@code VarHandle} and the name string corresponds to
2032 * the name of a signature-polymorphic access mode method, the resulting
2033 * method handle is equivalent to one produced by
2034 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2035 * the access mode corresponding to the name string and with the same
2036 * {@code type} arguments.
2037 * <p>
2038 * <b>Example:</b>
2039 * <blockquote><pre>{@code
2040 import static java.lang.invoke.MethodHandles.*;
2041 import static java.lang.invoke.MethodType.*;
2042 ...
2043 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2044 "concat", methodType(String.class, String.class));
2045 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2046 "hashCode", methodType(int.class));
2047 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2048 "hashCode", methodType(int.class));
2049 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2050 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2051 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2052 // interface method:
2053 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2054 "subSequence", methodType(CharSequence.class, int.class, int.class));
2055 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2056 // constructor "internal method" must be accessed differently:
2057 MethodType MT_newString = methodType(void.class); //()V for new String()
2058 try { assertEquals("impossible", lookup()
2059 .findVirtual(String.class, "<init>", MT_newString));
2060 } catch (NoSuchMethodException ex) { } // OK
2061 MethodHandle MH_newString = publicLookup()
2062 .findConstructor(String.class, MT_newString);
2063 assertEquals("", (String) MH_newString.invokeExact());
2064 * }</pre></blockquote>
2065 *
2066 * @param refc the class or interface from which the method is accessed
2067 * @param name the name of the method
2068 * @param type the type of the method, with the receiver argument omitted
2069 * @return the desired method handle
2070 * @throws NoSuchMethodException if the method does not exist
2071 * @throws IllegalAccessException if access checking fails,
2072 * or if the method is {@code static},
2073 * or if the method's variable arity modifier bit
2074 * is set and {@code asVarargsCollector} fails
2075 * @throws SecurityException if a security manager is present and it
2076 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2077 * @throws NullPointerException if any argument is null
2078 */
2079 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2080 if (refc == MethodHandle.class) {
2081 MethodHandle mh = findVirtualForMH(name, type);
2082 if (mh != null) return mh;
2083 } else if (refc == VarHandle.class) {
2084 MethodHandle mh = findVirtualForVH(name, type);
2085 if (mh != null) return mh;
2086 }
2087 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2088 MemberName method = resolveOrFail(refKind, refc, name, type);
2089 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
2090 }
2091 private MethodHandle findVirtualForMH(String name, MethodType type) {
2092 // these names require special lookups because of the implicit MethodType argument
2093 if ("invoke".equals(name))
2094 return invoker(type);
2095 if ("invokeExact".equals(name))
2096 return exactInvoker(type);
2097 assert(!MemberName.isMethodHandleInvokeName(name));
2098 return null;
2099 }
2100 private MethodHandle findVirtualForVH(String name, MethodType type) {
2101 try {
2102 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2103 } catch (IllegalArgumentException e) {
2104 return null;
2105 }
2106 }
2107
2108 /**
2109 * Produces a method handle which creates an object and initializes it, using
2110 * the constructor of the specified type.
2111 * The parameter types of the method handle will be those of the constructor,
2112 * while the return type will be a reference to the constructor's class.
2113 * The constructor and all its argument types must be accessible to the lookup object.
2114 * <p>
2115 * The requested type must have a return type of {@code void}.
2116 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2117 * <p>
2118 * The returned method handle will have
2119 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2120 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2121 * <p>
2122 * If the returned method handle is invoked, the constructor's class will
2123 * be initialized, if it has not already been initialized.
2124 * <p><b>Example:</b>
2125 * <blockquote><pre>{@code
2126 import static java.lang.invoke.MethodHandles.*;
2127 import static java.lang.invoke.MethodType.*;
2128 ...
2129 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2130 ArrayList.class, methodType(void.class, Collection.class));
2131 Collection orig = Arrays.asList("x", "y");
2132 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2133 assert(orig != copy);
2134 assertEquals(orig, copy);
2135 // a variable-arity constructor:
2136 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2137 ProcessBuilder.class, methodType(void.class, String[].class));
2138 ProcessBuilder pb = (ProcessBuilder)
2139 MH_newProcessBuilder.invoke("x", "y", "z");
2140 assertEquals("[x, y, z]", pb.command().toString());
2141 * }</pre></blockquote>
2142 * @param refc the class or interface from which the method is accessed
2143 * @param type the type of the method, with the receiver argument omitted, and a void return type
2144 * @return the desired method handle
2145 * @throws NoSuchMethodException if the constructor does not exist
2146 * @throws IllegalAccessException if access checking fails
2147 * or if the method's variable arity modifier bit
2148 * is set and {@code asVarargsCollector} fails
2149 * @throws SecurityException if a security manager is present and it
2150 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2151 * @throws NullPointerException if any argument is null
2152 */
2153 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2154 if (refc.isArray()) {
2155 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2156 }
2157 String name = "<init>";
2158 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2159 return getDirectConstructor(refc, ctor);
2160 }
2161
2162 /**
2163 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
2164 * initializer of the class is not run.
2165 * <p>
2166 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
2167 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
2168 * load the requested class, and then determines whether the class is accessible to this lookup object.
2169 *
2170 * @param targetName the fully qualified name of the class to be looked up.
2171 * @return the requested class.
2172 * @throws SecurityException if a security manager is present and it
2173 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2174 * @throws LinkageError if the linkage fails
2175 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2176 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2177 * modes.
2178 * @throws SecurityException if a security manager is present and it
2179 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2180 * @since 9
2181 */
2182 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2183 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2184 return accessClass(targetClass);
2185 }
2186
2187 /**
2188 * Determines if a class can be accessed from the lookup context defined by
2189 * this {@code Lookup} object. The static initializer of the class is not run.
2190 * <p>
2191 * If the {@code targetClass} is in the same module as the lookup class,
2192 * the lookup class is {@code LC} in module {@code M1} and
2193 * the previous lookup class is in module {@code M0} or
2194 * {@code null} if not present,
2195 * {@code targetClass} is accessible if and only if one of the following is true:
2196 * <ul>
2197 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2198 * {@code LC} or other class in the same nest of {@code LC}.</li>
2199 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2200 * in the same runtime package of {@code LC}.</li>
2201 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2202 * a public type in {@code M1}.</li>
2203 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2204 * a public type in a package exported by {@code M1} to at least {@code M0}
2205 * if the previous lookup class is present; otherwise, {@code targetClass}
2206 * is a public type in a package exported by {@code M1} unconditionally.</li>
2207 * </ul>
2208 *
2209 * <p>
2210 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2211 * can access public types in all modules when the type is in a package
2212 * that is exported unconditionally.
2213 * <p>
2214 * Otherwise, the target class is in a different module from {@code lookupClass},
2215 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2216 * is inaccessible.
2217 * <p>
2218 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2219 * {@code M1} is the module containing {@code lookupClass} and
2220 * {@code M2} is the module containing {@code targetClass},
2221 * then {@code targetClass} is accessible if and only if
2222 * <ul>
2223 * <li>{@code M1} reads {@code M2}, and
2224 * <li>{@code targetClass} is public and in a package exported by
2225 * {@code M2} at least to {@code M1}.
2226 * </ul>
2227 * <p>
2228 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2229 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2230 * containing the previous lookup class, then {@code targetClass} is accessible
2231 * if and only if one of the following is true:
2232 * <ul>
2233 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2234 * {@linkplain Module#reads reads} {@code M0} and the type is
2235 * in a package that is exported to at least {@code M1}.
2236 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2237 * {@linkplain Module#reads reads} {@code M1} and the type is
2238 * in a package that is exported to at least {@code M0}.
2239 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2240 * and {@code M1} reads {@code M2} and the type is in a package
2241 * that is exported to at least both {@code M0} and {@code M2}.
2242 * </ul>
2243 * <p>
2244 * Otherwise, {@code targetClass} is not accessible.
2245 *
2246 * @param targetClass the class to be access-checked
2247 * @return the class that has been access-checked
2248 * @throws IllegalAccessException if the class is not accessible from the lookup class
2249 * and previous lookup class, if present, using the allowed access modes.
2250 * @throws SecurityException if a security manager is present and it
2251 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2252 * @since 9
2253 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2254 */
2255 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2256 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2257 throw new MemberName(targetClass).makeAccessException("access violation", this);
2258 }
2259 checkSecurityManager(targetClass, null);
2260 return targetClass;
2261 }
2262
2263 /**
2264 * Produces an early-bound method handle for a virtual method.
2265 * It will bypass checks for overriding methods on the receiver,
2266 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2267 * instruction from within the explicitly specified {@code specialCaller}.
2268 * The type of the method handle will be that of the method,
2269 * with a suitably restricted receiver type prepended.
2270 * (The receiver type will be {@code specialCaller} or a subtype.)
2271 * The method and all its argument types must be accessible
2272 * to the lookup object.
2273 * <p>
2274 * Before method resolution,
2275 * if the explicitly specified caller class is not identical with the
2276 * lookup class, or if this lookup object does not have
2277 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2278 * privileges, the access fails.
2279 * <p>
2280 * The returned method handle will have
2281 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2282 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2283 * <p style="font-size:smaller;">
2284 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2285 * even though the {@code invokespecial} instruction can refer to them
2286 * in special circumstances. Use {@link #findConstructor findConstructor}
2287 * to access instance initialization methods in a safe manner.)</em>
2288 * <p><b>Example:</b>
2289 * <blockquote><pre>{@code
2290 import static java.lang.invoke.MethodHandles.*;
2291 import static java.lang.invoke.MethodType.*;
2292 ...
2293 static class Listie extends ArrayList {
2294 public String toString() { return "[wee Listie]"; }
2295 static Lookup lookup() { return MethodHandles.lookup(); }
2296 }
2297 ...
2298 // no access to constructor via invokeSpecial:
2299 MethodHandle MH_newListie = Listie.lookup()
2300 .findConstructor(Listie.class, methodType(void.class));
2301 Listie l = (Listie) MH_newListie.invokeExact();
2302 try { assertEquals("impossible", Listie.lookup().findSpecial(
2303 Listie.class, "<init>", methodType(void.class), Listie.class));
2304 } catch (NoSuchMethodException ex) { } // OK
2305 // access to super and self methods via invokeSpecial:
2306 MethodHandle MH_super = Listie.lookup().findSpecial(
2307 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2308 MethodHandle MH_this = Listie.lookup().findSpecial(
2309 Listie.class, "toString" , methodType(String.class), Listie.class);
2310 MethodHandle MH_duper = Listie.lookup().findSpecial(
2311 Object.class, "toString" , methodType(String.class), Listie.class);
2312 assertEquals("[]", (String) MH_super.invokeExact(l));
2313 assertEquals(""+l, (String) MH_this.invokeExact(l));
2314 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2315 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2316 String.class, "toString", methodType(String.class), Listie.class));
2317 } catch (IllegalAccessException ex) { } // OK
2318 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2319 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2320 * }</pre></blockquote>
2321 *
2322 * @param refc the class or interface from which the method is accessed
2323 * @param name the name of the method (which must not be "<init>")
2324 * @param type the type of the method, with the receiver argument omitted
2325 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2326 * @return the desired method handle
2327 * @throws NoSuchMethodException if the method does not exist
2328 * @throws IllegalAccessException if access checking fails,
2329 * or if the method is {@code static},
2330 * or if the method's variable arity modifier bit
2331 * is set and {@code asVarargsCollector} fails
2332 * @throws SecurityException if a security manager is present and it
2333 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2334 * @throws NullPointerException if any argument is null
2335 */
2336 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2337 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2338 checkSpecialCaller(specialCaller, refc);
2339 Lookup specialLookup = this.in(specialCaller);
2340 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2341 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
2342 }
2343
2344 /**
2345 * Produces a method handle giving read access to a non-static field.
2346 * The type of the method handle will have a return type of the field's
2347 * value type.
2348 * The method handle's single argument will be the instance containing
2349 * the field.
2350 * Access checking is performed immediately on behalf of the lookup class.
2351 * @param refc the class or interface from which the method is accessed
2352 * @param name the field's name
2353 * @param type the field's type
2354 * @return a method handle which can load values from the field
2355 * @throws NoSuchFieldException if the field does not exist
2356 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2357 * @throws SecurityException if a security manager is present and it
2358 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2359 * @throws NullPointerException if any argument is null
2360 * @see #findVarHandle(Class, String, Class)
2361 */
2362 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2363 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2364 return getDirectField(REF_getField, refc, field);
2365 }
2366
2367 /**
2368 * Produces a method handle giving write access to a non-static field.
2369 * The type of the method handle will have a void return type.
2370 * The method handle will take two arguments, the instance containing
2371 * the field, and the value to be stored.
2372 * The second argument will be of the field's value type.
2373 * Access checking is performed immediately on behalf of the lookup class.
2374 * @param refc the class or interface from which the method is accessed
2375 * @param name the field's name
2376 * @param type the field's type
2377 * @return a method handle which can store values into the field
2378 * @throws NoSuchFieldException if the field does not exist
2379 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2380 * or {@code final}
2381 * @throws SecurityException if a security manager is present and it
2382 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2383 * @throws NullPointerException if any argument is null
2384 * @see #findVarHandle(Class, String, Class)
2385 */
2386 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2387 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2388 return getDirectField(REF_putField, refc, field);
2389 }
2390
2391 /**
2392 * Produces a VarHandle giving access to a non-static field {@code name}
2393 * of type {@code type} declared in a class of type {@code recv}.
2394 * The VarHandle's variable type is {@code type} and it has one
2395 * coordinate type, {@code recv}.
2396 * <p>
2397 * Access checking is performed immediately on behalf of the lookup
2398 * class.
2399 * <p>
2400 * Certain access modes of the returned VarHandle are unsupported under
2401 * the following conditions:
2402 * <ul>
2403 * <li>if the field is declared {@code final}, then the write, atomic
2404 * update, numeric atomic update, and bitwise atomic update access
2405 * modes are unsupported.
2406 * <li>if the field type is anything other than {@code byte},
2407 * {@code short}, {@code char}, {@code int}, {@code long},
2408 * {@code float}, or {@code double} then numeric atomic update
2409 * access modes are unsupported.
2410 * <li>if the field type is anything other than {@code boolean},
2411 * {@code byte}, {@code short}, {@code char}, {@code int} or
2412 * {@code long} then bitwise atomic update access modes are
2413 * unsupported.
2414 * </ul>
2415 * <p>
2416 * If the field is declared {@code volatile} then the returned VarHandle
2417 * will override access to the field (effectively ignore the
2418 * {@code volatile} declaration) in accordance to its specified
2419 * access modes.
2420 * <p>
2421 * If the field type is {@code float} or {@code double} then numeric
2422 * and atomic update access modes compare values using their bitwise
2423 * representation (see {@link Float#floatToRawIntBits} and
2424 * {@link Double#doubleToRawLongBits}, respectively).
2425 * @apiNote
2426 * Bitwise comparison of {@code float} values or {@code double} values,
2427 * as performed by the numeric and atomic update access modes, differ
2428 * from the primitive {@code ==} operator and the {@link Float#equals}
2429 * and {@link Double#equals} methods, specifically with respect to
2430 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2431 * Care should be taken when performing a compare and set or a compare
2432 * and exchange operation with such values since the operation may
2433 * unexpectedly fail.
2434 * There are many possible NaN values that are considered to be
2435 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2436 * provided by Java can distinguish between them. Operation failure can
2437 * occur if the expected or witness value is a NaN value and it is
2438 * transformed (perhaps in a platform specific manner) into another NaN
2439 * value, and thus has a different bitwise representation (see
2440 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2441 * details).
2442 * The values {@code -0.0} and {@code +0.0} have different bitwise
2443 * representations but are considered equal when using the primitive
2444 * {@code ==} operator. Operation failure can occur if, for example, a
2445 * numeric algorithm computes an expected value to be say {@code -0.0}
2446 * and previously computed the witness value to be say {@code +0.0}.
2447 * @param recv the receiver class, of type {@code R}, that declares the
2448 * non-static field
2449 * @param name the field's name
2450 * @param type the field's type, of type {@code T}
2451 * @return a VarHandle giving access to non-static fields.
2452 * @throws NoSuchFieldException if the field does not exist
2453 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2454 * @throws SecurityException if a security manager is present and it
2455 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2456 * @throws NullPointerException if any argument is null
2457 * @since 9
2458 */
2459 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2460 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
2461 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
2462 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
2463 }
2464
2465 /**
2466 * Produces a method handle giving read access to a static field.
2467 * The type of the method handle will have a return type of the field's
2468 * value type.
2469 * The method handle will take no arguments.
2470 * Access checking is performed immediately on behalf of the lookup class.
2471 * <p>
2472 * If the returned method handle is invoked, the field's class will
2473 * be initialized, if it has not already been initialized.
2474 * @param refc the class or interface from which the method is accessed
2475 * @param name the field's name
2476 * @param type the field's type
2477 * @return a method handle which can load values from the field
2478 * @throws NoSuchFieldException if the field does not exist
2479 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2480 * @throws SecurityException if a security manager is present and it
2481 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2482 * @throws NullPointerException if any argument is null
2483 */
2484 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2485 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
2486 return getDirectField(REF_getStatic, refc, field);
2487 }
2488
2489 /**
2490 * Produces a method handle giving write access to a static field.
2491 * The type of the method handle will have a void return type.
2492 * The method handle will take a single
2493 * argument, of the field's value type, the value to be stored.
2494 * Access checking is performed immediately on behalf of the lookup class.
2495 * <p>
2496 * If the returned method handle is invoked, the field's class will
2497 * be initialized, if it has not already been initialized.
2498 * @param refc the class or interface from which the method is accessed
2499 * @param name the field's name
2500 * @param type the field's type
2501 * @return a method handle which can store values into the field
2502 * @throws NoSuchFieldException if the field does not exist
2503 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2504 * or is {@code final}
2505 * @throws SecurityException if a security manager is present and it
2506 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2507 * @throws NullPointerException if any argument is null
2508 */
2509 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2510 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
2511 return getDirectField(REF_putStatic, refc, field);
2512 }
2513
2514 /**
2515 * Produces a VarHandle giving access to a static field {@code name} of
2516 * type {@code type} declared in a class of type {@code decl}.
2517 * The VarHandle's variable type is {@code type} and it has no
2518 * coordinate types.
2519 * <p>
2520 * Access checking is performed immediately on behalf of the lookup
2521 * class.
2522 * <p>
2523 * If the returned VarHandle is operated on, the declaring class will be
2524 * initialized, if it has not already been initialized.
2525 * <p>
2526 * Certain access modes of the returned VarHandle are unsupported under
2527 * the following conditions:
2528 * <ul>
2529 * <li>if the field is declared {@code final}, then the write, atomic
2530 * update, numeric atomic update, and bitwise atomic update access
2531 * modes are unsupported.
2532 * <li>if the field type is anything other than {@code byte},
2533 * {@code short}, {@code char}, {@code int}, {@code long},
2534 * {@code float}, or {@code double}, then numeric atomic update
2535 * access modes are unsupported.
2536 * <li>if the field type is anything other than {@code boolean},
2537 * {@code byte}, {@code short}, {@code char}, {@code int} or
2538 * {@code long} then bitwise atomic update access modes are
2539 * unsupported.
2540 * </ul>
2541 * <p>
2542 * If the field is declared {@code volatile} then the returned VarHandle
2543 * will override access to the field (effectively ignore the
2544 * {@code volatile} declaration) in accordance to its specified
2545 * access modes.
2546 * <p>
2547 * If the field type is {@code float} or {@code double} then numeric
2548 * and atomic update access modes compare values using their bitwise
2549 * representation (see {@link Float#floatToRawIntBits} and
2550 * {@link Double#doubleToRawLongBits}, respectively).
2551 * @apiNote
2552 * Bitwise comparison of {@code float} values or {@code double} values,
2553 * as performed by the numeric and atomic update access modes, differ
2554 * from the primitive {@code ==} operator and the {@link Float#equals}
2555 * and {@link Double#equals} methods, specifically with respect to
2556 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2557 * Care should be taken when performing a compare and set or a compare
2558 * and exchange operation with such values since the operation may
2559 * unexpectedly fail.
2560 * There are many possible NaN values that are considered to be
2561 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2562 * provided by Java can distinguish between them. Operation failure can
2563 * occur if the expected or witness value is a NaN value and it is
2564 * transformed (perhaps in a platform specific manner) into another NaN
2565 * value, and thus has a different bitwise representation (see
2566 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2567 * details).
2568 * The values {@code -0.0} and {@code +0.0} have different bitwise
2569 * representations but are considered equal when using the primitive
2570 * {@code ==} operator. Operation failure can occur if, for example, a
2571 * numeric algorithm computes an expected value to be say {@code -0.0}
2572 * and previously computed the witness value to be say {@code +0.0}.
2573 * @param decl the class that declares the static field
2574 * @param name the field's name
2575 * @param type the field's type, of type {@code T}
2576 * @return a VarHandle giving access to a static field
2577 * @throws NoSuchFieldException if the field does not exist
2578 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2579 * @throws SecurityException if a security manager is present and it
2580 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2581 * @throws NullPointerException if any argument is null
2582 * @since 9
2583 */
2584 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2585 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
2586 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
2587 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
2588 }
2589
2590 /**
2591 * Produces an early-bound method handle for a non-static method.
2592 * The receiver must have a supertype {@code defc} in which a method
2593 * of the given name and type is accessible to the lookup class.
2594 * The method and all its argument types must be accessible to the lookup object.
2595 * The type of the method handle will be that of the method,
2596 * without any insertion of an additional receiver parameter.
2597 * The given receiver will be bound into the method handle,
2598 * so that every call to the method handle will invoke the
2599 * requested method on the given receiver.
2600 * <p>
2601 * The returned method handle will have
2602 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2603 * the method's variable arity modifier bit ({@code 0x0080}) is set
2604 * <em>and</em> the trailing array argument is not the only argument.
2605 * (If the trailing array argument is the only argument,
2606 * the given receiver value will be bound to it.)
2607 * <p>
2608 * This is almost equivalent to the following code, with some differences noted below:
2609 * <blockquote><pre>{@code
2610 import static java.lang.invoke.MethodHandles.*;
2611 import static java.lang.invoke.MethodType.*;
2612 ...
2613 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
2614 MethodHandle mh1 = mh0.bindTo(receiver);
2615 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
2616 return mh1;
2617 * }</pre></blockquote>
2618 * where {@code defc} is either {@code receiver.getClass()} or a super
2619 * type of that class, in which the requested method is accessible
2620 * to the lookup class.
2621 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
2622 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
2623 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
2624 * the receiver is restricted by {@code findVirtual} to the lookup class.)
2625 * @param receiver the object from which the method is accessed
2626 * @param name the name of the method
2627 * @param type the type of the method, with the receiver argument omitted
2628 * @return the desired method handle
2629 * @throws NoSuchMethodException if the method does not exist
2630 * @throws IllegalAccessException if access checking fails
2631 * or if the method's variable arity modifier bit
2632 * is set and {@code asVarargsCollector} fails
2633 * @throws SecurityException if a security manager is present and it
2634 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2635 * @throws NullPointerException if any argument is null
2636 * @see MethodHandle#bindTo
2637 * @see #findVirtual
2638 */
2639 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2640 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2641 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2642 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
2643 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2644 throw new IllegalAccessException("The restricted defining class " +
2645 mh.type().leadingReferenceParameter().getName() +
2646 " is not assignable from receiver class " +
2647 receiver.getClass().getName());
2648 }
2649 return mh.bindArgumentL(0, receiver).setVarargs(method);
2650 }
2651
2652 /**
2653 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2654 * to <i>m</i>, if the lookup class has permission.
2655 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2656 * If <i>m</i> is virtual, overriding is respected on every call.
2657 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2658 * The type of the method handle will be that of the method,
2659 * with the receiver type prepended (but only if it is non-static).
2660 * If the method's {@code accessible} flag is not set,
2661 * access checking is performed immediately on behalf of the lookup class.
2662 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2663 * <p>
2664 * The returned method handle will have
2665 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2666 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2667 * <p>
2668 * If <i>m</i> is static, and
2669 * if the returned method handle is invoked, the method's class will
2670 * be initialized, if it has not already been initialized.
2671 * @param m the reflected method
2672 * @return a method handle which can invoke the reflected method
2673 * @throws IllegalAccessException if access checking fails
2674 * or if the method's variable arity modifier bit
2675 * is set and {@code asVarargsCollector} fails
2676 * @throws NullPointerException if the argument is null
2677 */
2678 public MethodHandle unreflect(Method m) throws IllegalAccessException {
2679 if (m.getDeclaringClass() == MethodHandle.class) {
2680 MethodHandle mh = unreflectForMH(m);
2681 if (mh != null) return mh;
2682 }
2683 if (m.getDeclaringClass() == VarHandle.class) {
2684 MethodHandle mh = unreflectForVH(m);
2685 if (mh != null) return mh;
2686 }
2687 MemberName method = new MemberName(m);
2688 byte refKind = method.getReferenceKind();
2689 if (refKind == REF_invokeSpecial)
2690 refKind = REF_invokeVirtual;
2691 assert(method.isMethod());
2692 @SuppressWarnings("deprecation")
2693 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
2694 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
2695 }
2696 private MethodHandle unreflectForMH(Method m) {
2697 // these names require special lookups because they throw UnsupportedOperationException
2698 if (MemberName.isMethodHandleInvokeName(m.getName()))
2699 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
2700 return null;
2701 }
2702 private MethodHandle unreflectForVH(Method m) {
2703 // these names require special lookups because they throw UnsupportedOperationException
2704 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
2705 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
2706 return null;
2707 }
2708
2709 /**
2710 * Produces a method handle for a reflected method.
2711 * It will bypass checks for overriding methods on the receiver,
2712 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2713 * instruction from within the explicitly specified {@code specialCaller}.
2714 * The type of the method handle will be that of the method,
2715 * with a suitably restricted receiver type prepended.
2716 * (The receiver type will be {@code specialCaller} or a subtype.)
2717 * If the method's {@code accessible} flag is not set,
2718 * access checking is performed immediately on behalf of the lookup class,
2719 * as if {@code invokespecial} instruction were being linked.
2720 * <p>
2721 * Before method resolution,
2722 * if the explicitly specified caller class is not identical with the
2723 * lookup class, or if this lookup object does not have
2724 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2725 * privileges, the access fails.
2726 * <p>
2727 * The returned method handle will have
2728 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2729 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2730 * @param m the reflected method
2731 * @param specialCaller the class nominally calling the method
2732 * @return a method handle which can invoke the reflected method
2733 * @throws IllegalAccessException if access checking fails,
2734 * or if the method is {@code static},
2735 * or if the method's variable arity modifier bit
2736 * is set and {@code asVarargsCollector} fails
2737 * @throws NullPointerException if any argument is null
2738 */
2739 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
2740 checkSpecialCaller(specialCaller, m.getDeclaringClass());
2741 Lookup specialLookup = this.in(specialCaller);
2742 MemberName method = new MemberName(m, true);
2743 assert(method.isMethod());
2744 // ignore m.isAccessible: this is a new kind of access
2745 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
2746 }
2747
2748 /**
2749 * Produces a method handle for a reflected constructor.
2750 * The type of the method handle will be that of the constructor,
2751 * with the return type changed to the declaring class.
2752 * The method handle will perform a {@code newInstance} operation,
2753 * creating a new instance of the constructor's class on the
2754 * arguments passed to the method handle.
2755 * <p>
2756 * If the constructor's {@code accessible} flag is not set,
2757 * access checking is performed immediately on behalf of the lookup class.
2758 * <p>
2759 * The returned method handle will have
2760 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2761 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2762 * <p>
2763 * If the returned method handle is invoked, the constructor's class will
2764 * be initialized, if it has not already been initialized.
2765 * @param c the reflected constructor
2766 * @return a method handle which can invoke the reflected constructor
2767 * @throws IllegalAccessException if access checking fails
2768 * or if the method's variable arity modifier bit
2769 * is set and {@code asVarargsCollector} fails
2770 * @throws NullPointerException if the argument is null
2771 */
2772 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
2773 MemberName ctor = new MemberName(c);
2774 assert(ctor.isConstructor());
2775 @SuppressWarnings("deprecation")
2776 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
2777 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
2778 }
2779
2780 /**
2781 * Produces a method handle giving read access to a reflected field.
2782 * The type of the method handle will have a return type of the field's
2783 * value type.
2784 * If the field is {@code static}, the method handle will take no arguments.
2785 * Otherwise, its single argument will be the instance containing
2786 * the field.
2787 * If the {@code Field} object's {@code accessible} flag is not set,
2788 * access checking is performed immediately on behalf of the lookup class.
2789 * <p>
2790 * If the field is static, and
2791 * if the returned method handle is invoked, the field's class will
2792 * be initialized, if it has not already been initialized.
2793 * @param f the reflected field
2794 * @return a method handle which can load values from the reflected field
2795 * @throws IllegalAccessException if access checking fails
2796 * @throws NullPointerException if the argument is null
2797 */
2798 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
2799 return unreflectField(f, false);
2800 }
2801
2802 /**
2803 * Produces a method handle giving write access to a reflected field.
2804 * The type of the method handle will have a void return type.
2805 * If the field is {@code static}, the method handle will take a single
2806 * argument, of the field's value type, the value to be stored.
2807 * Otherwise, the two arguments will be the instance containing
2808 * the field, and the value to be stored.
2809 * If the {@code Field} object's {@code accessible} flag is not set,
2810 * access checking is performed immediately on behalf of the lookup class.
2811 * <p>
2812 * If the field is {@code final}, write access will not be
2813 * allowed and access checking will fail, except under certain
2814 * narrow circumstances documented for {@link Field#set Field.set}.
2815 * A method handle is returned only if a corresponding call to
2816 * the {@code Field} object's {@code set} method could return
2817 * normally. In particular, fields which are both {@code static}
2818 * and {@code final} may never be set.
2819 * <p>
2820 * If the field is {@code static}, and
2821 * if the returned method handle is invoked, the field's class will
2822 * be initialized, if it has not already been initialized.
2823 * @param f the reflected field
2824 * @return a method handle which can store values into the reflected field
2825 * @throws IllegalAccessException if access checking fails,
2826 * or if the field is {@code final} and write access
2827 * is not enabled on the {@code Field} object
2828 * @throws NullPointerException if the argument is null
2829 */
2830 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
2831 return unreflectField(f, true);
2832 }
2833
2834 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
2835 MemberName field = new MemberName(f, isSetter);
2836 if (isSetter && field.isStatic() && field.isFinal())
2837 throw field.makeAccessException("static final field has no write access", this);
2838 assert(isSetter
2839 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
2840 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
2841 @SuppressWarnings("deprecation")
2842 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
2843 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
2844 }
2845
2846 /**
2847 * Produces a VarHandle giving access to a reflected field {@code f}
2848 * of type {@code T} declared in a class of type {@code R}.
2849 * The VarHandle's variable type is {@code T}.
2850 * If the field is non-static the VarHandle has one coordinate type,
2851 * {@code R}. Otherwise, the field is static, and the VarHandle has no
2852 * coordinate types.
2853 * <p>
2854 * Access checking is performed immediately on behalf of the lookup
2855 * class, regardless of the value of the field's {@code accessible}
2856 * flag.
2857 * <p>
2858 * If the field is static, and if the returned VarHandle is operated
2859 * on, the field's declaring class will be initialized, if it has not
2860 * already been initialized.
2861 * <p>
2862 * Certain access modes of the returned VarHandle are unsupported under
2863 * the following conditions:
2864 * <ul>
2865 * <li>if the field is declared {@code final}, then the write, atomic
2866 * update, numeric atomic update, and bitwise atomic update access
2867 * modes are unsupported.
2868 * <li>if the field type is anything other than {@code byte},
2869 * {@code short}, {@code char}, {@code int}, {@code long},
2870 * {@code float}, or {@code double} then numeric atomic update
2871 * access modes are unsupported.
2872 * <li>if the field type is anything other than {@code boolean},
2873 * {@code byte}, {@code short}, {@code char}, {@code int} or
2874 * {@code long} then bitwise atomic update access modes are
2875 * unsupported.
2876 * </ul>
2877 * <p>
2878 * If the field is declared {@code volatile} then the returned VarHandle
2879 * will override access to the field (effectively ignore the
2880 * {@code volatile} declaration) in accordance to its specified
2881 * access modes.
2882 * <p>
2883 * If the field type is {@code float} or {@code double} then numeric
2884 * and atomic update access modes compare values using their bitwise
2885 * representation (see {@link Float#floatToRawIntBits} and
2886 * {@link Double#doubleToRawLongBits}, respectively).
2887 * @apiNote
2888 * Bitwise comparison of {@code float} values or {@code double} values,
2889 * as performed by the numeric and atomic update access modes, differ
2890 * from the primitive {@code ==} operator and the {@link Float#equals}
2891 * and {@link Double#equals} methods, specifically with respect to
2892 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2893 * Care should be taken when performing a compare and set or a compare
2894 * and exchange operation with such values since the operation may
2895 * unexpectedly fail.
2896 * There are many possible NaN values that are considered to be
2897 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2898 * provided by Java can distinguish between them. Operation failure can
2899 * occur if the expected or witness value is a NaN value and it is
2900 * transformed (perhaps in a platform specific manner) into another NaN
2901 * value, and thus has a different bitwise representation (see
2902 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2903 * details).
2904 * The values {@code -0.0} and {@code +0.0} have different bitwise
2905 * representations but are considered equal when using the primitive
2906 * {@code ==} operator. Operation failure can occur if, for example, a
2907 * numeric algorithm computes an expected value to be say {@code -0.0}
2908 * and previously computed the witness value to be say {@code +0.0}.
2909 * @param f the reflected field, with a field of type {@code T}, and
2910 * a declaring class of type {@code R}
2911 * @return a VarHandle giving access to non-static fields or a static
2912 * field
2913 * @throws IllegalAccessException if access checking fails
2914 * @throws NullPointerException if the argument is null
2915 * @since 9
2916 */
2917 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
2918 MemberName getField = new MemberName(f, false);
2919 MemberName putField = new MemberName(f, true);
2920 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
2921 f.getDeclaringClass(), getField, putField);
2922 }
2923
2924 /**
2925 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2926 * created by this lookup object or a similar one.
2927 * Security and access checks are performed to ensure that this lookup object
2928 * is capable of reproducing the target method handle.
2929 * This means that the cracking may fail if target is a direct method handle
2930 * but was created by an unrelated lookup object.
2931 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
2932 * and was created by a lookup object for a different class.
2933 * @param target a direct method handle to crack into symbolic reference components
2934 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
2935 * @throws SecurityException if a security manager is present and it
2936 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2937 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
2938 * @throws NullPointerException if the target is {@code null}
2939 * @see MethodHandleInfo
2940 * @since 1.8
2941 */
2942 public MethodHandleInfo revealDirect(MethodHandle target) {
2943 MemberName member = target.internalMemberName();
2944 if (member == null || (!member.isResolved() &&
2945 !member.isMethodHandleInvoke() &&
2946 !member.isVarHandleMethodInvoke()))
2947 throw newIllegalArgumentException("not a direct method handle");
2948 Class<?> defc = member.getDeclaringClass();
2949 byte refKind = member.getReferenceKind();
2950 assert(MethodHandleNatives.refKindIsValid(refKind));
2951 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2952 // Devirtualized method invocation is usually formally virtual.
2953 // To avoid creating extra MemberName objects for this common case,
2954 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2955 refKind = REF_invokeVirtual;
2956 if (refKind == REF_invokeVirtual && defc.isInterface())
2957 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2958 refKind = REF_invokeInterface;
2959 // Check SM permissions and member access before cracking.
2960 try {
2961 checkAccess(refKind, defc, member);
2962 checkSecurityManager(defc, member);
2963 } catch (IllegalAccessException ex) {
2964 throw new IllegalArgumentException(ex);
2965 }
2966 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2967 Class<?> callerClass = target.internalCallerClass();
2968 if (!hasPrivateAccess() || callerClass != lookupClass())
2969 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2970 }
2971 // Produce the handle to the results.
2972 return new InfoFromMemberName(this, member, refKind);
2973 }
2974
2975 /// Helper methods, all package-private.
2976
2977 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2978 checkSymbolicClass(refc); // do this before attempting to resolve
2979 Objects.requireNonNull(name);
2980 Objects.requireNonNull(type);
2981 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2982 NoSuchFieldException.class);
2983 }
2984
2985 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2986 checkSymbolicClass(refc); // do this before attempting to resolve
2987 Objects.requireNonNull(name);
2988 Objects.requireNonNull(type);
2989 checkMethodName(refKind, name); // NPE check on name
2990 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2991 NoSuchMethodException.class);
2992 }
2993
2994 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2995 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2996 Objects.requireNonNull(member.getName());
2997 Objects.requireNonNull(member.getType());
2998 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2999 ReflectiveOperationException.class);
3000 }
3001
3002 MemberName resolveOrNull(byte refKind, MemberName member) {
3003 // do this before attempting to resolve
3004 if (!isClassAccessible(member.getDeclaringClass())) {
3005 return null;
3006 }
3007 Objects.requireNonNull(member.getName());
3008 Objects.requireNonNull(member.getType());
3009 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
3010 }
3011
3012 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3013 if (!isClassAccessible(refc)) {
3014 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3015 }
3016 }
3017
3018 boolean isClassAccessible(Class<?> refc) {
3019 Objects.requireNonNull(refc);
3020 Class<?> caller = lookupClassOrNull();
3021 return caller == null || VerifyAccess.isClassAccessible(refc, caller, prevLookupClass, allowedModes);
3022 }
3023
3024 /** Check name for an illegal leading "<" character. */
3025 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3026 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3027 throw new NoSuchMethodException("illegal method name: "+name);
3028 }
3029
3030
3031 /**
3032 * Find my trustable caller class if m is a caller sensitive method.
3033 * If this lookup object has private access, then the caller class is the lookupClass.
3034 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3035 */
3036 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
3037 Class<?> callerClass = null;
3038 if (MethodHandleNatives.isCallerSensitive(m)) {
3039 // Only lookups with private access are allowed to resolve caller-sensitive methods
3040 if (hasPrivateAccess()) {
3041 callerClass = lookupClass;
3042 } else {
3043 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3044 }
3045 }
3046 return callerClass;
3047 }
3048
3049 /**
3050 * Returns {@code true} if this lookup has {@code PRIVATE} access.
3051 * @return {@code true} if this lookup has {@code PRIVATE} access.
3052 * @since 9
3053 */
3054 public boolean hasPrivateAccess() {
3055 return (allowedModes & PRIVATE) != 0;
3056 }
3057
3058 /**
3059 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3060 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3061 * If this lookup object has private access, then the caller class is the lookupClass.
3062 */
3063 void checkSecurityManager(Class<?> refc, MemberName m) {
3064 SecurityManager smgr = System.getSecurityManager();
3065 if (smgr == null) return;
3066 if (allowedModes == TRUSTED) return;
3067
3068 // Step 1:
3069 boolean fullPowerLookup = hasPrivateAccess();
3070 if (!fullPowerLookup ||
3071 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3072 ReflectUtil.checkPackageAccess(refc);
3073 }
3074
3075 if (m == null) { // findClass or accessClass
3076 // Step 2b:
3077 if (!fullPowerLookup) {
3078 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3079 }
3080 return;
3081 }
3082
3083 // Step 2a:
3084 if (m.isPublic()) return;
3085 if (!fullPowerLookup) {
3086 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3087 }
3088
3089 // Step 3:
3090 Class<?> defc = m.getDeclaringClass();
3091 if (!fullPowerLookup && defc != refc) {
3092 ReflectUtil.checkPackageAccess(defc);
3093 }
3094 }
3095
3096 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3097 boolean wantStatic = (refKind == REF_invokeStatic);
3098 String message;
3099 if (m.isConstructor())
3100 message = "expected a method, not a constructor";
3101 else if (!m.isMethod())
3102 message = "expected a method";
3103 else if (wantStatic != m.isStatic())
3104 message = wantStatic ? "expected a static method" : "expected a non-static method";
3105 else
3106 { checkAccess(refKind, refc, m); return; }
3107 throw m.makeAccessException(message, this);
3108 }
3109
3110 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3111 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3112 String message;
3113 if (wantStatic != m.isStatic())
3114 message = wantStatic ? "expected a static field" : "expected a non-static field";
3115 else
3116 { checkAccess(refKind, refc, m); return; }
3117 throw m.makeAccessException(message, this);
3118 }
3119
3120 /** Check public/protected/private bits on the symbolic reference class and its member. */
3121 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3122 assert(m.referenceKindIsConsistentWith(refKind) &&
3123 MethodHandleNatives.refKindIsValid(refKind) &&
3124 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3125 int allowedModes = this.allowedModes;
3126 if (allowedModes == TRUSTED) return;
3127 int mods = m.getModifiers();
3128 if (Modifier.isProtected(mods) &&
3129 refKind == REF_invokeVirtual &&
3130 m.getDeclaringClass() == Object.class &&
3131 m.getName().equals("clone") &&
3132 refc.isArray()) {
3133 // The JVM does this hack also.
3134 // (See ClassVerifier::verify_invoke_instructions
3135 // and LinkResolver::check_method_accessability.)
3136 // Because the JVM does not allow separate methods on array types,
3137 // there is no separate method for int[].clone.
3138 // All arrays simply inherit Object.clone.
3139 // But for access checking logic, we make Object.clone
3140 // (normally protected) appear to be public.
3141 // Later on, when the DirectMethodHandle is created,
3142 // its leading argument will be restricted to the
3143 // requested array type.
3144 // N.B. The return type is not adjusted, because
3145 // that is *not* the bytecode behavior.
3146 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3147 }
3148 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3149 // cannot "new" a protected ctor in a different package
3150 mods ^= Modifier.PROTECTED;
3151 }
3152 if (Modifier.isFinal(mods) &&
3153 MethodHandleNatives.refKindIsSetter(refKind))
3154 throw m.makeAccessException("unexpected set of a final field", this);
3155 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3156 if ((requestedModes & allowedModes) != 0) {
3157 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3158 mods, lookupClass(), previousLookupClass(), allowedModes))
3159 return;
3160 } else {
3161 // Protected members can also be checked as if they were package-private.
3162 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3163 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3164 return;
3165 }
3166 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3167 }
3168
3169 String accessFailedMessage(Class<?> refc, MemberName m) {
3170 Class<?> defc = m.getDeclaringClass();
3171 int mods = m.getModifiers();
3172 // check the class first:
3173 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3174 (defc == refc ||
3175 Modifier.isPublic(refc.getModifiers())));
3176 if (!classOK && (allowedModes & PACKAGE) != 0) {
3177 // ignore previous lookup class to check if default package access
3178 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3179 (defc == refc ||
3180 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3181 }
3182 if (!classOK)
3183 return "class is not public";
3184 if (Modifier.isPublic(mods))
3185 return "access to public member failed"; // (how?, module not readable?)
3186 if (Modifier.isPrivate(mods))
3187 return "member is private";
3188 if (Modifier.isProtected(mods))
3189 return "member is protected";
3190 return "member is private to package";
3191 }
3192
3193 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3194 int allowedModes = this.allowedModes;
3195 if (allowedModes == TRUSTED) return;
3196 if (!hasPrivateAccess()
3197 || (specialCaller != lookupClass()
3198 // ensure non-abstract methods in superinterfaces can be special-invoked
3199 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3200 throw new MemberName(specialCaller).
3201 makeAccessException("no private access for invokespecial", this);
3202 }
3203
3204 private boolean restrictProtectedReceiver(MemberName method) {
3205 // The accessing class only has the right to use a protected member
3206 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3207 if (!method.isProtected() || method.isStatic()
3208 || allowedModes == TRUSTED
3209 || method.getDeclaringClass() == lookupClass()
3210 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3211 return false;
3212 return true;
3213 }
3214 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3215 assert(!method.isStatic());
3216 // receiver type of mh is too wide; narrow to caller
3217 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3218 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3219 }
3220 MethodType rawType = mh.type();
3221 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3222 MethodType narrowType = rawType.changeParameterType(0, caller);
3223 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3224 assert(mh.viewAsTypeChecks(narrowType, true));
3225 return mh.copyWith(narrowType, mh.form);
3226 }
3227
3228 /** Check access and get the requested method. */
3229 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
3230 final boolean doRestrict = true;
3231 final boolean checkSecurity = true;
3232 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
3233 }
3234 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3235 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
3236 final boolean doRestrict = false;
3237 final boolean checkSecurity = true;
3238 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
3239 }
3240 /** Check access and get the requested method, eliding security manager checks. */
3241 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
3242 final boolean doRestrict = true;
3243 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3244 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
3245 }
3246 /** Common code for all methods; do not call directly except from immediately above. */
3247 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3248 boolean checkSecurity,
3249 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
3250
3251 checkMethod(refKind, refc, method);
3252 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3253 if (checkSecurity)
3254 checkSecurityManager(refc, method);
3255 assert(!method.isMethodHandleInvoke());
3256
3257 if (refKind == REF_invokeSpecial &&
3258 refc != lookupClass() &&
3259 !refc.isInterface() &&
3260 refc != lookupClass().getSuperclass() &&
3261 refc.isAssignableFrom(lookupClass())) {
3262 assert(!method.getName().equals("<init>")); // not this code path
3263
3264 // Per JVMS 6.5, desc. of invokespecial instruction:
3265 // If the method is in a superclass of the LC,
3266 // and if our original search was above LC.super,
3267 // repeat the search (symbolic lookup) from LC.super
3268 // and continue with the direct superclass of that class,
3269 // and so forth, until a match is found or no further superclasses exist.
3270 // FIXME: MemberName.resolve should handle this instead.
3271 Class<?> refcAsSuper = lookupClass();
3272 MemberName m2;
3273 do {
3274 refcAsSuper = refcAsSuper.getSuperclass();
3275 m2 = new MemberName(refcAsSuper,
3276 method.getName(),
3277 method.getMethodType(),
3278 REF_invokeSpecial);
3279 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
3280 } while (m2 == null && // no method is found yet
3281 refc != refcAsSuper); // search up to refc
3282 if (m2 == null) throw new InternalError(method.toString());
3283 method = m2;
3284 refc = refcAsSuper;
3285 // redo basic checks
3286 checkMethod(refKind, refc, method);
3287 }
3288
3289 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3290 MethodHandle mh = dmh;
3291 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3292 if ((doRestrict && refKind == REF_invokeSpecial) ||
3293 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
3294 mh = restrictReceiver(method, dmh, lookupClass());
3295 }
3296 mh = maybeBindCaller(method, mh, boundCallerClass);
3297 mh = mh.setVarargs(method);
3298 return mh;
3299 }
3300 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
3301 Class<?> boundCallerClass)
3302 throws IllegalAccessException {
3303 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3304 return mh;
3305 Class<?> hostClass = lookupClass;
3306 if (!hasPrivateAccess()) // caller must have private access
3307 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
3308 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
3309 // Note: caller will apply varargs after this step happens.
3310 return cbmh;
3311 }
3312 /** Check access and get the requested field. */
3313 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3314 final boolean checkSecurity = true;
3315 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3316 }
3317 /** Check access and get the requested field, eliding security manager checks. */
3318 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3319 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3320 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3321 }
3322 /** Common code for all fields; do not call directly except from immediately above. */
3323 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
3324 boolean checkSecurity) throws IllegalAccessException {
3325 checkField(refKind, refc, field);
3326 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3327 if (checkSecurity)
3328 checkSecurityManager(refc, field);
3329 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3330 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3331 restrictProtectedReceiver(field));
3332 if (doRestrict)
3333 return restrictReceiver(field, dmh, lookupClass());
3334 return dmh;
3335 }
3336 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3337 Class<?> refc, MemberName getField, MemberName putField)
3338 throws IllegalAccessException {
3339 final boolean checkSecurity = true;
3340 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3341 }
3342 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
3343 Class<?> refc, MemberName getField, MemberName putField)
3344 throws IllegalAccessException {
3345 final boolean checkSecurity = false;
3346 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3347 }
3348 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3349 Class<?> refc, MemberName getField, MemberName putField,
3350 boolean checkSecurity) throws IllegalAccessException {
3351 assert getField.isStatic() == putField.isStatic();
3352 assert getField.isGetter() && putField.isSetter();
3353 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3354 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3355
3356 checkField(getRefKind, refc, getField);
3357 if (checkSecurity)
3358 checkSecurityManager(refc, getField);
3359
3360 if (!putField.isFinal()) {
3361 // A VarHandle does not support updates to final fields, any
3362 // such VarHandle to a final field will be read-only and
3363 // therefore the following write-based accessibility checks are
3364 // only required for non-final fields
3365 checkField(putRefKind, refc, putField);
3366 if (checkSecurity)
3367 checkSecurityManager(refc, putField);
3368 }
3369
3370 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3371 restrictProtectedReceiver(getField));
3372 if (doRestrict) {
3373 assert !getField.isStatic();
3374 // receiver type of VarHandle is too wide; narrow to caller
3375 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3376 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3377 }
3378 refc = lookupClass();
3379 }
3380 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
3381 }
3382 /** Check access and get the requested constructor. */
3383 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3384 final boolean checkSecurity = true;
3385 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3386 }
3387 /** Check access and get the requested constructor, eliding security manager checks. */
3388 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3389 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3390 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3391 }
3392 /** Common code for all constructors; do not call directly except from immediately above. */
3393 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
3394 boolean checkSecurity) throws IllegalAccessException {
3395 assert(ctor.isConstructor());
3396 checkAccess(REF_newInvokeSpecial, refc, ctor);
3397 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3398 if (checkSecurity)
3399 checkSecurityManager(refc, ctor);
3400 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3401 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3402 }
3403
3404 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3405 */
3406 /*non-public*/
3407 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
3408 throws ReflectiveOperationException {
3409 if (!(type instanceof Class || type instanceof MethodType))
3410 throw new InternalError("unresolved MemberName");
3411 MemberName member = new MemberName(refKind, defc, name, type);
3412 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3413 if (mh != null) {
3414 checkSymbolicClass(defc);
3415 return mh;
3416 }
3417 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3418 // Treat MethodHandle.invoke and invokeExact specially.
3419 mh = findVirtualForMH(member.getName(), member.getMethodType());
3420 if (mh != null) {
3421 return mh;
3422 }
3423 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3424 // Treat signature-polymorphic methods on VarHandle specially.
3425 mh = findVirtualForVH(member.getName(), member.getMethodType());
3426 if (mh != null) {
3427 return mh;
3428 }
3429 }
3430 MemberName resolved = resolveOrFail(refKind, member);
3431 mh = getDirectMethodForConstant(refKind, defc, resolved);
3432 if (mh instanceof DirectMethodHandle
3433 && canBeCached(refKind, defc, resolved)) {
3434 MemberName key = mh.internalMemberName();
3435 if (key != null) {
3436 key = key.asNormalOriginal();
3437 }
3438 if (member.equals(key)) { // better safe than sorry
3439 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
3440 }
3441 }
3442 return mh;
3443 }
3444 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
3445 if (refKind == REF_invokeSpecial) {
3446 return false;
3447 }
3448 if (!Modifier.isPublic(defc.getModifiers()) ||
3449 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
3450 !member.isPublic() ||
3451 member.isCallerSensitive()) {
3452 return false;
3453 }
3454 ClassLoader loader = defc.getClassLoader();
3455 if (loader != null) {
3456 ClassLoader sysl = ClassLoader.getSystemClassLoader();
3457 boolean found = false;
3458 while (sysl != null) {
3459 if (loader == sysl) { found = true; break; }
3460 sysl = sysl.getParent();
3461 }
3462 if (!found) {
3463 return false;
3464 }
3465 }
3466 try {
3467 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
3468 new MemberName(refKind, defc, member.getName(), member.getType()));
3469 if (resolved2 == null) {
3470 return false;
3471 }
3472 checkSecurityManager(defc, resolved2);
3473 } catch (SecurityException ex) {
3474 return false;
3475 }
3476 return true;
3477 }
3478 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
3479 throws ReflectiveOperationException {
3480 if (MethodHandleNatives.refKindIsField(refKind)) {
3481 return getDirectFieldNoSecurityManager(refKind, defc, member);
3482 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
3483 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
3484 } else if (refKind == REF_newInvokeSpecial) {
3485 return getDirectConstructorNoSecurityManager(defc, member);
3486 }
3487 // oops
3488 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
3489 }
3490
3491 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
3492
3493 /**
3494 * The set of class options that specify whether a hidden class created by
3495 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
3496 * Lookup::defineHiddenMethod} method is dynamically added as
3497 * a new member to the nest of a lookup class and whether a hidden class
3498 * is weakly referenced by its defining class loader.
3499 *
3500 * @since 14
3501 */
3502 public enum ClassOption {
3503 /**
3504 * This class option specifies the hidden class be added to
3505 * {@linkplain Class#getNestHost nest} of a lookup class as
3506 * a nestmate.
3507 *
3508 * <p> A hidden nestmate class has access to the private members of all
3509 * classes and interfaces in the same nest.
3510 *
3511 * @see Class#getNestHost()
3512 */
3513 NESTMATE(NESTMATE_CLASS),
3514
3515 /**
3516 * This class option specifies the hidden class be weakly
3517 * referenced by its defining class loader such that it
3518 * may be unloaded while its defining class loader is
3519 * <a href="../ref/package.html#reachability">strongly reachable</a>.
3520 *
3521 * @jls 12.7 Unloading of Classes and Interfaces
3522 */
3523 WEAK(WEAK_CLASS);
3524
3525 /* the flag value is used by VM at define class time */
3526 private final int flag;
3527 ClassOption(int flag) {
3528 this.flag = flag;
3529 }
3530
3531 static int optionsToFlag(Set<ClassOption> options) {
3532 int flags = 0;
3533 for (ClassOption cp : options) {
3534 flags |= cp.flag;
3535 }
3536 return flags;
3537 }
3538 }
3539 }
3540
3541 /**
3542 * Produces a method handle constructing arrays of a desired type,
3543 * as if by the {@code anewarray} bytecode.
3544 * The return type of the method handle will be the array type.
3545 * The type of its sole argument will be {@code int}, which specifies the size of the array.
3546 *
3547 * <p> If the returned method handle is invoked with a negative
3548 * array size, a {@code NegativeArraySizeException} will be thrown.
3549 *
3550 * @param arrayClass an array type
3551 * @return a method handle which can create arrays of the given type
3552 * @throws NullPointerException if the argument is {@code null}
3553 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
3554 * @see java.lang.reflect.Array#newInstance(Class, int)
3555 * @jvms 6.5 {@code anewarray} Instruction
3556 * @since 9
3557 */
3558 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
3559 if (!arrayClass.isArray()) {
3560 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
3561 }
3562 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
3563 bindTo(arrayClass.getComponentType());
3564 return ani.asType(ani.type().changeReturnType(arrayClass));
3565 }
3566
3567 /**
3568 * Produces a method handle returning the length of an array,
3569 * as if by the {@code arraylength} bytecode.
3570 * The type of the method handle will have {@code int} as return type,
3571 * and its sole argument will be the array type.
3572 *
3573 * <p> If the returned method handle is invoked with a {@code null}
3574 * array reference, a {@code NullPointerException} will be thrown.
3575 *
3576 * @param arrayClass an array type
3577 * @return a method handle which can retrieve the length of an array of the given array type
3578 * @throws NullPointerException if the argument is {@code null}
3579 * @throws IllegalArgumentException if arrayClass is not an array type
3580 * @jvms 6.5 {@code arraylength} Instruction
3581 * @since 9
3582 */
3583 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
3584 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
3585 }
3586
3587 /**
3588 * Produces a method handle giving read access to elements of an array,
3589 * as if by the {@code aaload} bytecode.
3590 * The type of the method handle will have a return type of the array's
3591 * element type. Its first argument will be the array type,
3592 * and the second will be {@code int}.
3593 *
3594 * <p> When the returned method handle is invoked,
3595 * the array reference and array index are checked.
3596 * A {@code NullPointerException} will be thrown if the array reference
3597 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3598 * thrown if the index is negative or if it is greater than or equal to
3599 * the length of the array.
3600 *
3601 * @param arrayClass an array type
3602 * @return a method handle which can load values from the given array type
3603 * @throws NullPointerException if the argument is null
3604 * @throws IllegalArgumentException if arrayClass is not an array type
3605 * @jvms 6.5 {@code aaload} Instruction
3606 */
3607 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
3608 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
3609 }
3610
3611 /**
3612 * Produces a method handle giving write access to elements of an array,
3613 * as if by the {@code astore} bytecode.
3614 * The type of the method handle will have a void return type.
3615 * Its last argument will be the array's element type.
3616 * The first and second arguments will be the array type and int.
3617 *
3618 * <p> When the returned method handle is invoked,
3619 * the array reference and array index are checked.
3620 * A {@code NullPointerException} will be thrown if the array reference
3621 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3622 * thrown if the index is negative or if it is greater than or equal to
3623 * the length of the array.
3624 *
3625 * @param arrayClass the class of an array
3626 * @return a method handle which can store values into the array type
3627 * @throws NullPointerException if the argument is null
3628 * @throws IllegalArgumentException if arrayClass is not an array type
3629 * @jvms 6.5 {@code aastore} Instruction
3630 */
3631 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
3632 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
3633 }
3634
3635 /**
3636 * Produces a VarHandle giving access to elements of an array of type
3637 * {@code arrayClass}. The VarHandle's variable type is the component type
3638 * of {@code arrayClass} and the list of coordinate types is
3639 * {@code (arrayClass, int)}, where the {@code int} coordinate type
3640 * corresponds to an argument that is an index into an array.
3641 * <p>
3642 * Certain access modes of the returned VarHandle are unsupported under
3643 * the following conditions:
3644 * <ul>
3645 * <li>if the component type is anything other than {@code byte},
3646 * {@code short}, {@code char}, {@code int}, {@code long},
3647 * {@code float}, or {@code double} then numeric atomic update access
3648 * modes are unsupported.
3649 * <li>if the field type is anything other than {@code boolean},
3650 * {@code byte}, {@code short}, {@code char}, {@code int} or
3651 * {@code long} then bitwise atomic update access modes are
3652 * unsupported.
3653 * </ul>
3654 * <p>
3655 * If the component type is {@code float} or {@code double} then numeric
3656 * and atomic update access modes compare values using their bitwise
3657 * representation (see {@link Float#floatToRawIntBits} and
3658 * {@link Double#doubleToRawLongBits}, respectively).
3659 *
3660 * <p> When the returned {@code VarHandle} is invoked,
3661 * the array reference and array index are checked.
3662 * A {@code NullPointerException} will be thrown if the array reference
3663 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3664 * thrown if the index is negative or if it is greater than or equal to
3665 * the length of the array.
3666 *
3667 * @apiNote
3668 * Bitwise comparison of {@code float} values or {@code double} values,
3669 * as performed by the numeric and atomic update access modes, differ
3670 * from the primitive {@code ==} operator and the {@link Float#equals}
3671 * and {@link Double#equals} methods, specifically with respect to
3672 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3673 * Care should be taken when performing a compare and set or a compare
3674 * and exchange operation with such values since the operation may
3675 * unexpectedly fail.
3676 * There are many possible NaN values that are considered to be
3677 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3678 * provided by Java can distinguish between them. Operation failure can
3679 * occur if the expected or witness value is a NaN value and it is
3680 * transformed (perhaps in a platform specific manner) into another NaN
3681 * value, and thus has a different bitwise representation (see
3682 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3683 * details).
3684 * The values {@code -0.0} and {@code +0.0} have different bitwise
3685 * representations but are considered equal when using the primitive
3686 * {@code ==} operator. Operation failure can occur if, for example, a
3687 * numeric algorithm computes an expected value to be say {@code -0.0}
3688 * and previously computed the witness value to be say {@code +0.0}.
3689 * @param arrayClass the class of an array, of type {@code T[]}
3690 * @return a VarHandle giving access to elements of an array
3691 * @throws NullPointerException if the arrayClass is null
3692 * @throws IllegalArgumentException if arrayClass is not an array type
3693 * @since 9
3694 */
3695 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
3696 return VarHandles.makeArrayElementHandle(arrayClass);
3697 }
3698
3699 /**
3700 * Produces a VarHandle giving access to elements of a {@code byte[]} array
3701 * viewed as if it were a different primitive array type, such as
3702 * {@code int[]} or {@code long[]}.
3703 * The VarHandle's variable type is the component type of
3704 * {@code viewArrayClass} and the list of coordinate types is
3705 * {@code (byte[], int)}, where the {@code int} coordinate type
3706 * corresponds to an argument that is an index into a {@code byte[]} array.
3707 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
3708 * array, composing bytes to or from a value of the component type of
3709 * {@code viewArrayClass} according to the given endianness.
3710 * <p>
3711 * The supported component types (variables types) are {@code short},
3712 * {@code char}, {@code int}, {@code long}, {@code float} and
3713 * {@code double}.
3714 * <p>
3715 * Access of bytes at a given index will result in an
3716 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3717 * or greater than the {@code byte[]} array length minus the size (in bytes)
3718 * of {@code T}.
3719 * <p>
3720 * Access of bytes at an index may be aligned or misaligned for {@code T},
3721 * with respect to the underlying memory address, {@code A} say, associated
3722 * with the array and index.
3723 * If access is misaligned then access for anything other than the
3724 * {@code get} and {@code set} access modes will result in an
3725 * {@code IllegalStateException}. In such cases atomic access is only
3726 * guaranteed with respect to the largest power of two that divides the GCD
3727 * of {@code A} and the size (in bytes) of {@code T}.
3728 * If access is aligned then following access modes are supported and are
3729 * guaranteed to support atomic access:
3730 * <ul>
3731 * <li>read write access modes for all {@code T}, with the exception of
3732 * access modes {@code get} and {@code set} for {@code long} and
3733 * {@code double} on 32-bit platforms.
3734 * <li>atomic update access modes for {@code int}, {@code long},
3735 * {@code float} or {@code double}.
3736 * (Future major platform releases of the JDK may support additional
3737 * types for certain currently unsupported access modes.)
3738 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3739 * (Future major platform releases of the JDK may support additional
3740 * numeric types for certain currently unsupported access modes.)
3741 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3742 * (Future major platform releases of the JDK may support additional
3743 * numeric types for certain currently unsupported access modes.)
3744 * </ul>
3745 * <p>
3746 * Misaligned access, and therefore atomicity guarantees, may be determined
3747 * for {@code byte[]} arrays without operating on a specific array. Given
3748 * an {@code index}, {@code T} and it's corresponding boxed type,
3749 * {@code T_BOX}, misalignment may be determined as follows:
3750 * <pre>{@code
3751 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3752 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
3753 * alignmentOffset(0, sizeOfT);
3754 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
3755 * boolean isMisaligned = misalignedAtIndex != 0;
3756 * }</pre>
3757 * <p>
3758 * If the variable type is {@code float} or {@code double} then atomic
3759 * update access modes compare values using their bitwise representation
3760 * (see {@link Float#floatToRawIntBits} and
3761 * {@link Double#doubleToRawLongBits}, respectively).
3762 * @param viewArrayClass the view array class, with a component type of
3763 * type {@code T}
3764 * @param byteOrder the endianness of the view array elements, as
3765 * stored in the underlying {@code byte} array
3766 * @return a VarHandle giving access to elements of a {@code byte[]} array
3767 * viewed as if elements corresponding to the components type of the view
3768 * array class
3769 * @throws NullPointerException if viewArrayClass or byteOrder is null
3770 * @throws IllegalArgumentException if viewArrayClass is not an array type
3771 * @throws UnsupportedOperationException if the component type of
3772 * viewArrayClass is not supported as a variable type
3773 * @since 9
3774 */
3775 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
3776 ByteOrder byteOrder) throws IllegalArgumentException {
3777 Objects.requireNonNull(byteOrder);
3778 return VarHandles.byteArrayViewHandle(viewArrayClass,
3779 byteOrder == ByteOrder.BIG_ENDIAN);
3780 }
3781
3782 /**
3783 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
3784 * viewed as if it were an array of elements of a different primitive
3785 * component type to that of {@code byte}, such as {@code int[]} or
3786 * {@code long[]}.
3787 * The VarHandle's variable type is the component type of
3788 * {@code viewArrayClass} and the list of coordinate types is
3789 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
3790 * corresponds to an argument that is an index into a {@code byte[]} array.
3791 * The returned VarHandle accesses bytes at an index in a
3792 * {@code ByteBuffer}, composing bytes to or from a value of the component
3793 * type of {@code viewArrayClass} according to the given endianness.
3794 * <p>
3795 * The supported component types (variables types) are {@code short},
3796 * {@code char}, {@code int}, {@code long}, {@code float} and
3797 * {@code double}.
3798 * <p>
3799 * Access will result in a {@code ReadOnlyBufferException} for anything
3800 * other than the read access modes if the {@code ByteBuffer} is read-only.
3801 * <p>
3802 * Access of bytes at a given index will result in an
3803 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3804 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
3805 * {@code T}.
3806 * <p>
3807 * Access of bytes at an index may be aligned or misaligned for {@code T},
3808 * with respect to the underlying memory address, {@code A} say, associated
3809 * with the {@code ByteBuffer} and index.
3810 * If access is misaligned then access for anything other than the
3811 * {@code get} and {@code set} access modes will result in an
3812 * {@code IllegalStateException}. In such cases atomic access is only
3813 * guaranteed with respect to the largest power of two that divides the GCD
3814 * of {@code A} and the size (in bytes) of {@code T}.
3815 * If access is aligned then following access modes are supported and are
3816 * guaranteed to support atomic access:
3817 * <ul>
3818 * <li>read write access modes for all {@code T}, with the exception of
3819 * access modes {@code get} and {@code set} for {@code long} and
3820 * {@code double} on 32-bit platforms.
3821 * <li>atomic update access modes for {@code int}, {@code long},
3822 * {@code float} or {@code double}.
3823 * (Future major platform releases of the JDK may support additional
3824 * types for certain currently unsupported access modes.)
3825 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3826 * (Future major platform releases of the JDK may support additional
3827 * numeric types for certain currently unsupported access modes.)
3828 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3829 * (Future major platform releases of the JDK may support additional
3830 * numeric types for certain currently unsupported access modes.)
3831 * </ul>
3832 * <p>
3833 * Misaligned access, and therefore atomicity guarantees, may be determined
3834 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
3835 * {@code index}, {@code T} and it's corresponding boxed type,
3836 * {@code T_BOX}, as follows:
3837 * <pre>{@code
3838 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3839 * ByteBuffer bb = ...
3840 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
3841 * boolean isMisaligned = misalignedAtIndex != 0;
3842 * }</pre>
3843 * <p>
3844 * If the variable type is {@code float} or {@code double} then atomic
3845 * update access modes compare values using their bitwise representation
3846 * (see {@link Float#floatToRawIntBits} and
3847 * {@link Double#doubleToRawLongBits}, respectively).
3848 * @param viewArrayClass the view array class, with a component type of
3849 * type {@code T}
3850 * @param byteOrder the endianness of the view array elements, as
3851 * stored in the underlying {@code ByteBuffer} (Note this overrides the
3852 * endianness of a {@code ByteBuffer})
3853 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
3854 * viewed as if elements corresponding to the components type of the view
3855 * array class
3856 * @throws NullPointerException if viewArrayClass or byteOrder is null
3857 * @throws IllegalArgumentException if viewArrayClass is not an array type
3858 * @throws UnsupportedOperationException if the component type of
3859 * viewArrayClass is not supported as a variable type
3860 * @since 9
3861 */
3862 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
3863 ByteOrder byteOrder) throws IllegalArgumentException {
3864 Objects.requireNonNull(byteOrder);
3865 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
3866 byteOrder == ByteOrder.BIG_ENDIAN);
3867 }
3868
3869
3870 /// method handle invocation (reflective style)
3871
3872 /**
3873 * Produces a method handle which will invoke any method handle of the
3874 * given {@code type}, with a given number of trailing arguments replaced by
3875 * a single trailing {@code Object[]} array.
3876 * The resulting invoker will be a method handle with the following
3877 * arguments:
3878 * <ul>
3879 * <li>a single {@code MethodHandle} target
3880 * <li>zero or more leading values (counted by {@code leadingArgCount})
3881 * <li>an {@code Object[]} array containing trailing arguments
3882 * </ul>
3883 * <p>
3884 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
3885 * the indicated {@code type}.
3886 * That is, if the target is exactly of the given {@code type}, it will behave
3887 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
3888 * is used to convert the target to the required {@code type}.
3889 * <p>
3890 * The type of the returned invoker will not be the given {@code type}, but rather
3891 * will have all parameters except the first {@code leadingArgCount}
3892 * replaced by a single array of type {@code Object[]}, which will be
3893 * the final parameter.
3894 * <p>
3895 * Before invoking its target, the invoker will spread the final array, apply
3896 * reference casts as necessary, and unbox and widen primitive arguments.
3897 * If, when the invoker is called, the supplied array argument does
3898 * not have the correct number of elements, the invoker will throw
3899 * an {@link IllegalArgumentException} instead of invoking the target.
3900 * <p>
3901 * This method is equivalent to the following code (though it may be more efficient):
3902 * <blockquote><pre>{@code
3903 MethodHandle invoker = MethodHandles.invoker(type);
3904 int spreadArgCount = type.parameterCount() - leadingArgCount;
3905 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
3906 return invoker;
3907 * }</pre></blockquote>
3908 * This method throws no reflective or security exceptions.
3909 * @param type the desired target type
3910 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
3911 * @return a method handle suitable for invoking any method handle of the given type
3912 * @throws NullPointerException if {@code type} is null
3913 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
3914 * the range from 0 to {@code type.parameterCount()} inclusive,
3915 * or if the resulting method handle's type would have
3916 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3917 */
3918 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
3919 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
3920 throw newIllegalArgumentException("bad argument count", leadingArgCount);
3921 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
3922 return type.invokers().spreadInvoker(leadingArgCount);
3923 }
3924
3925 /**
3926 * Produces a special <em>invoker method handle</em> which can be used to
3927 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
3928 * The resulting invoker will have a type which is
3929 * exactly equal to the desired type, except that it will accept
3930 * an additional leading argument of type {@code MethodHandle}.
3931 * <p>
3932 * This method is equivalent to the following code (though it may be more efficient):
3933 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
3934 *
3935 * <p style="font-size:smaller;">
3936 * <em>Discussion:</em>
3937 * Invoker method handles can be useful when working with variable method handles
3938 * of unknown types.
3939 * For example, to emulate an {@code invokeExact} call to a variable method
3940 * handle {@code M}, extract its type {@code T},
3941 * look up the invoker method {@code X} for {@code T},
3942 * and call the invoker method, as {@code X.invoke(T, A...)}.
3943 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
3944 * is unknown.)
3945 * If spreading, collecting, or other argument transformations are required,
3946 * they can be applied once to the invoker {@code X} and reused on many {@code M}
3947 * method handle values, as long as they are compatible with the type of {@code X}.
3948 * <p style="font-size:smaller;">
3949 * <em>(Note: The invoker method is not available via the Core Reflection API.
3950 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3951 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3952 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3953 * <p>
3954 * This method throws no reflective or security exceptions.
3955 * @param type the desired target type
3956 * @return a method handle suitable for invoking any method handle of the given type
3957 * @throws IllegalArgumentException if the resulting method handle's type would have
3958 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3959 */
3960 public static MethodHandle exactInvoker(MethodType type) {
3961 return type.invokers().exactInvoker();
3962 }
3963
3964 /**
3965 * Produces a special <em>invoker method handle</em> which can be used to
3966 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
3967 * The resulting invoker will have a type which is
3968 * exactly equal to the desired type, except that it will accept
3969 * an additional leading argument of type {@code MethodHandle}.
3970 * <p>
3971 * Before invoking its target, if the target differs from the expected type,
3972 * the invoker will apply reference casts as
3973 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
3974 * Similarly, the return value will be converted as necessary.
3975 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
3976 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
3977 * <p>
3978 * This method is equivalent to the following code (though it may be more efficient):
3979 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
3980 * <p style="font-size:smaller;">
3981 * <em>Discussion:</em>
3982 * A {@linkplain MethodType#genericMethodType general method type} is one which
3983 * mentions only {@code Object} arguments and return values.
3984 * An invoker for such a type is capable of calling any method handle
3985 * of the same arity as the general type.
3986 * <p style="font-size:smaller;">
3987 * <em>(Note: The invoker method is not available via the Core Reflection API.
3988 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3989 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3990 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3991 * <p>
3992 * This method throws no reflective or security exceptions.
3993 * @param type the desired target type
3994 * @return a method handle suitable for invoking any method handle convertible to the given type
3995 * @throws IllegalArgumentException if the resulting method handle's type would have
3996 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3997 */
3998 public static MethodHandle invoker(MethodType type) {
3999 return type.invokers().genericInvoker();
4000 }
4001
4002 /**
4003 * Produces a special <em>invoker method handle</em> which can be used to
4004 * invoke a signature-polymorphic access mode method on any VarHandle whose
4005 * associated access mode type is compatible with the given type.
4006 * The resulting invoker will have a type which is exactly equal to the
4007 * desired given type, except that it will accept an additional leading
4008 * argument of type {@code VarHandle}.
4009 *
4010 * @param accessMode the VarHandle access mode
4011 * @param type the desired target type
4012 * @return a method handle suitable for invoking an access mode method of
4013 * any VarHandle whose access mode type is of the given type.
4014 * @since 9
4015 */
4016 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4017 return type.invokers().varHandleMethodExactInvoker(accessMode);
4018 }
4019
4020 /**
4021 * Produces a special <em>invoker method handle</em> which can be used to
4022 * invoke a signature-polymorphic access mode method on any VarHandle whose
4023 * associated access mode type is compatible with the given type.
4024 * The resulting invoker will have a type which is exactly equal to the
4025 * desired given type, except that it will accept an additional leading
4026 * argument of type {@code VarHandle}.
4027 * <p>
4028 * Before invoking its target, if the access mode type differs from the
4029 * desired given type, the invoker will apply reference casts as necessary
4030 * and box, unbox, or widen primitive values, as if by
4031 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4032 * converted as necessary.
4033 * <p>
4034 * This method is equivalent to the following code (though it may be more
4035 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4036 *
4037 * @param accessMode the VarHandle access mode
4038 * @param type the desired target type
4039 * @return a method handle suitable for invoking an access mode method of
4040 * any VarHandle whose access mode type is convertible to the given
4041 * type.
4042 * @since 9
4043 */
4044 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4045 return type.invokers().varHandleMethodInvoker(accessMode);
4046 }
4047
4048 /*non-public*/
4049 static MethodHandle basicInvoker(MethodType type) {
4050 return type.invokers().basicInvoker();
4051 }
4052
4053 /// method handle modification (creation from other method handles)
4054
4055 /**
4056 * Produces a method handle which adapts the type of the
4057 * given method handle to a new type by pairwise argument and return type conversion.
4058 * The original type and new type must have the same number of arguments.
4059 * The resulting method handle is guaranteed to report a type
4060 * which is equal to the desired new type.
4061 * <p>
4062 * If the original type and new type are equal, returns target.
4063 * <p>
4064 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4065 * and some additional conversions are also applied if those conversions fail.
4066 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4067 * if possible, before or instead of any conversions done by {@code asType}:
4068 * <ul>
4069 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4070 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4071 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4072 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4073 * the boolean is converted to a byte value, 1 for true, 0 for false.
4074 * (This treatment follows the usage of the bytecode verifier.)
4075 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4076 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
4077 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4078 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4079 * then a Java casting conversion (JLS 5.5) is applied.
4080 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4081 * widening and/or narrowing.)
4082 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4083 * conversion will be applied at runtime, possibly followed
4084 * by a Java casting conversion (JLS 5.5) on the primitive value,
4085 * possibly followed by a conversion from byte to boolean by testing
4086 * the low-order bit.
4087 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4088 * and if the reference is null at runtime, a zero value is introduced.
4089 * </ul>
4090 * @param target the method handle to invoke after arguments are retyped
4091 * @param newType the expected type of the new method handle
4092 * @return a method handle which delegates to the target after performing
4093 * any necessary argument conversions, and arranges for any
4094 * necessary return value conversions
4095 * @throws NullPointerException if either argument is null
4096 * @throws WrongMethodTypeException if the conversion cannot be made
4097 * @see MethodHandle#asType
4098 */
4099 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4100 explicitCastArgumentsChecks(target, newType);
4101 // use the asTypeCache when possible:
4102 MethodType oldType = target.type();
4103 if (oldType == newType) return target;
4104 if (oldType.explicitCastEquivalentToAsType(newType)) {
4105 return target.asFixedArity().asType(newType);
4106 }
4107 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4108 }
4109
4110 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4111 if (target.type().parameterCount() != newType.parameterCount()) {
4112 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4113 }
4114 }
4115
4116 /**
4117 * Produces a method handle which adapts the calling sequence of the
4118 * given method handle to a new type, by reordering the arguments.
4119 * The resulting method handle is guaranteed to report a type
4120 * which is equal to the desired new type.
4121 * <p>
4122 * The given array controls the reordering.
4123 * Call {@code #I} the number of incoming parameters (the value
4124 * {@code newType.parameterCount()}, and call {@code #O} the number
4125 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4126 * Then the length of the reordering array must be {@code #O},
4127 * and each element must be a non-negative number less than {@code #I}.
4128 * For every {@code N} less than {@code #O}, the {@code N}-th
4129 * outgoing argument will be taken from the {@code I}-th incoming
4130 * argument, where {@code I} is {@code reorder[N]}.
4131 * <p>
4132 * No argument or return value conversions are applied.
4133 * The type of each incoming argument, as determined by {@code newType},
4134 * must be identical to the type of the corresponding outgoing parameter
4135 * or parameters in the target method handle.
4136 * The return type of {@code newType} must be identical to the return
4137 * type of the original target.
4138 * <p>
4139 * The reordering array need not specify an actual permutation.
4140 * An incoming argument will be duplicated if its index appears
4141 * more than once in the array, and an incoming argument will be dropped
4142 * if its index does not appear in the array.
4143 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4144 * incoming arguments which are not mentioned in the reordering array
4145 * may be of any type, as determined only by {@code newType}.
4146 * <blockquote><pre>{@code
4147 import static java.lang.invoke.MethodHandles.*;
4148 import static java.lang.invoke.MethodType.*;
4149 ...
4150 MethodType intfn1 = methodType(int.class, int.class);
4151 MethodType intfn2 = methodType(int.class, int.class, int.class);
4152 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4153 assert(sub.type().equals(intfn2));
4154 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4155 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4156 assert((int)rsub.invokeExact(1, 100) == 99);
4157 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4158 assert(add.type().equals(intfn2));
4159 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4160 assert(twice.type().equals(intfn1));
4161 assert((int)twice.invokeExact(21) == 42);
4162 * }</pre></blockquote>
4163 * <p>
4164 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4165 * variable-arity method handle}, even if the original target method handle was.
4166 * @param target the method handle to invoke after arguments are reordered
4167 * @param newType the expected type of the new method handle
4168 * @param reorder an index array which controls the reordering
4169 * @return a method handle which delegates to the target after it
4170 * drops unused arguments and moves and/or duplicates the other arguments
4171 * @throws NullPointerException if any argument is null
4172 * @throws IllegalArgumentException if the index array length is not equal to
4173 * the arity of the target, or if any index array element
4174 * not a valid index for a parameter of {@code newType},
4175 * or if two corresponding parameter types in
4176 * {@code target.type()} and {@code newType} are not identical,
4177 */
4178 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4179 reorder = reorder.clone(); // get a private copy
4180 MethodType oldType = target.type();
4181 permuteArgumentChecks(reorder, newType, oldType);
4182 // first detect dropped arguments and handle them separately
4183 int[] originalReorder = reorder;
4184 BoundMethodHandle result = target.rebind();
4185 LambdaForm form = result.form;
4186 int newArity = newType.parameterCount();
4187 // Normalize the reordering into a real permutation,
4188 // by removing duplicates and adding dropped elements.
4189 // This somewhat improves lambda form caching, as well
4190 // as simplifying the transform by breaking it up into steps.
4191 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4192 if (ddIdx > 0) {
4193 // We found a duplicated entry at reorder[ddIdx].
4194 // Example: (x,y,z)->asList(x,y,z)
4195 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4196 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4197 // The starred element corresponds to the argument
4198 // deleted by the dupArgumentForm transform.
4199 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4200 boolean killFirst = false;
4201 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4202 // Set killFirst if the dup is larger than an intervening position.
4203 // This will remove at least one inversion from the permutation.
4204 if (dupVal > val) killFirst = true;
4205 }
4206 if (!killFirst) {
4207 srcPos = dstPos;
4208 dstPos = ddIdx;
4209 }
4210 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4211 assert (reorder[srcPos] == reorder[dstPos]);
4212 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4213 // contract the reordering by removing the element at dstPos
4214 int tailPos = dstPos + 1;
4215 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4216 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4217 } else {
4218 int dropVal = ~ddIdx, insPos = 0;
4219 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4220 // Find first element of reorder larger than dropVal.
4221 // This is where we will insert the dropVal.
4222 insPos += 1;
4223 }
4224 Class<?> ptype = newType.parameterType(dropVal);
4225 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4226 oldType = oldType.insertParameterTypes(insPos, ptype);
4227 // expand the reordering by inserting an element at insPos
4228 int tailPos = insPos + 1;
4229 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4230 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4231 reorder[insPos] = dropVal;
4232 }
4233 assert (permuteArgumentChecks(reorder, newType, oldType));
4234 }
4235 assert (reorder.length == newArity); // a perfect permutation
4236 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4237 form = form.editor().permuteArgumentsForm(1, reorder);
4238 if (newType == result.type() && form == result.internalForm())
4239 return result;
4240 return result.copyWith(newType, form);
4241 }
4242
4243 /**
4244 * Return an indication of any duplicate or omission in reorder.
4245 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4246 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4247 * Otherwise, return zero.
4248 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4249 */
4250 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4251 final int BIT_LIMIT = 63; // max number of bits in bit mask
4252 if (newArity < BIT_LIMIT) {
4253 long mask = 0;
4254 for (int i = 0; i < reorder.length; i++) {
4255 int arg = reorder[i];
4256 if (arg >= newArity) {
4257 return reorder.length;
4258 }
4259 long bit = 1L << arg;
4260 if ((mask & bit) != 0) {
4261 return i; // >0 indicates a dup
4262 }
4263 mask |= bit;
4264 }
4265 if (mask == (1L << newArity) - 1) {
4266 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4267 return 0;
4268 }
4269 // find first zero
4270 long zeroBit = Long.lowestOneBit(~mask);
4271 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4272 assert(zeroPos <= newArity);
4273 if (zeroPos == newArity) {
4274 return 0;
4275 }
4276 return ~zeroPos;
4277 } else {
4278 // same algorithm, different bit set
4279 BitSet mask = new BitSet(newArity);
4280 for (int i = 0; i < reorder.length; i++) {
4281 int arg = reorder[i];
4282 if (arg >= newArity) {
4283 return reorder.length;
4284 }
4285 if (mask.get(arg)) {
4286 return i; // >0 indicates a dup
4287 }
4288 mask.set(arg);
4289 }
4290 int zeroPos = mask.nextClearBit(0);
4291 assert(zeroPos <= newArity);
4292 if (zeroPos == newArity) {
4293 return 0;
4294 }
4295 return ~zeroPos;
4296 }
4297 }
4298
4299 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4300 if (newType.returnType() != oldType.returnType())
4301 throw newIllegalArgumentException("return types do not match",
4302 oldType, newType);
4303 if (reorder.length == oldType.parameterCount()) {
4304 int limit = newType.parameterCount();
4305 boolean bad = false;
4306 for (int j = 0; j < reorder.length; j++) {
4307 int i = reorder[j];
4308 if (i < 0 || i >= limit) {
4309 bad = true; break;
4310 }
4311 Class<?> src = newType.parameterType(i);
4312 Class<?> dst = oldType.parameterType(j);
4313 if (src != dst)
4314 throw newIllegalArgumentException("parameter types do not match after reorder",
4315 oldType, newType);
4316 }
4317 if (!bad) return true;
4318 }
4319 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
4320 }
4321
4322 /**
4323 * Produces a method handle of the requested return type which returns the given
4324 * constant value every time it is invoked.
4325 * <p>
4326 * Before the method handle is returned, the passed-in value is converted to the requested type.
4327 * If the requested type is primitive, widening primitive conversions are attempted,
4328 * else reference conversions are attempted.
4329 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4330 * @param type the return type of the desired method handle
4331 * @param value the value to return
4332 * @return a method handle of the given return type and no arguments, which always returns the given value
4333 * @throws NullPointerException if the {@code type} argument is null
4334 * @throws ClassCastException if the value cannot be converted to the required return type
4335 * @throws IllegalArgumentException if the given type is {@code void.class}
4336 */
4337 public static MethodHandle constant(Class<?> type, Object value) {
4338 if (type.isPrimitive()) {
4339 if (type == void.class)
4340 throw newIllegalArgumentException("void type");
4341 Wrapper w = Wrapper.forPrimitiveType(type);
4342 value = w.convert(value, type);
4343 if (w.zero().equals(value))
4344 return zero(w, type);
4345 return insertArguments(identity(type), 0, value);
4346 } else {
4347 if (value == null)
4348 return zero(Wrapper.OBJECT, type);
4349 return identity(type).bindTo(value);
4350 }
4351 }
4352
4353 /**
4354 * Produces a method handle which returns its sole argument when invoked.
4355 * @param type the type of the sole parameter and return value of the desired method handle
4356 * @return a unary method handle which accepts and returns the given type
4357 * @throws NullPointerException if the argument is null
4358 * @throws IllegalArgumentException if the given type is {@code void.class}
4359 */
4360 public static MethodHandle identity(Class<?> type) {
4361 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4362 int pos = btw.ordinal();
4363 MethodHandle ident = IDENTITY_MHS[pos];
4364 if (ident == null) {
4365 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4366 }
4367 if (ident.type().returnType() == type)
4368 return ident;
4369 // something like identity(Foo.class); do not bother to intern these
4370 assert (btw == Wrapper.OBJECT);
4371 return makeIdentity(type);
4372 }
4373
4374 /**
4375 * Produces a constant method handle of the requested return type which
4376 * returns the default value for that type every time it is invoked.
4377 * The resulting constant method handle will have no side effects.
4378 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4379 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4380 * since {@code explicitCastArguments} converts {@code null} to default values.
4381 * @param type the expected return type of the desired method handle
4382 * @return a constant method handle that takes no arguments
4383 * and returns the default value of the given type (or void, if the type is void)
4384 * @throws NullPointerException if the argument is null
4385 * @see MethodHandles#constant
4386 * @see MethodHandles#empty
4387 * @see MethodHandles#explicitCastArguments
4388 * @since 9
4389 */
4390 public static MethodHandle zero(Class<?> type) {
4391 Objects.requireNonNull(type);
4392 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
4393 }
4394
4395 private static MethodHandle identityOrVoid(Class<?> type) {
4396 return type == void.class ? zero(type) : identity(type);
4397 }
4398
4399 /**
4400 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4401 * and returns a suitable default depending on the return type.
4402 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4403 * <p>The returned method handle is equivalent to
4404 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4405 *
4406 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4407 * {@code guardWithTest(pred, target, empty(target.type())}.
4408 * @param type the type of the desired method handle
4409 * @return a constant method handle of the given type, which returns a default value of the given return type
4410 * @throws NullPointerException if the argument is null
4411 * @see MethodHandles#zero
4412 * @see MethodHandles#constant
4413 * @since 9
4414 */
4415 public static MethodHandle empty(MethodType type) {
4416 Objects.requireNonNull(type);
4417 return dropArguments(zero(type.returnType()), 0, type.parameterList());
4418 }
4419
4420 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4421 private static MethodHandle makeIdentity(Class<?> ptype) {
4422 MethodType mtype = methodType(ptype, ptype);
4423 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4424 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4425 }
4426
4427 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
4428 int pos = btw.ordinal();
4429 MethodHandle zero = ZERO_MHS[pos];
4430 if (zero == null) {
4431 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
4432 }
4433 if (zero.type().returnType() == rtype)
4434 return zero;
4435 assert(btw == Wrapper.OBJECT);
4436 return makeZero(rtype);
4437 }
4438 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4439 private static MethodHandle makeZero(Class<?> rtype) {
4440 MethodType mtype = methodType(rtype);
4441 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
4442 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
4443 }
4444
4445 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4446 // Simulate a CAS, to avoid racy duplication of results.
4447 MethodHandle prev = cache[pos];
4448 if (prev != null) return prev;
4449 return cache[pos] = value;
4450 }
4451
4452 /**
4453 * Provides a target method handle with one or more <em>bound arguments</em>
4454 * in advance of the method handle's invocation.
4455 * The formal parameters to the target corresponding to the bound
4456 * arguments are called <em>bound parameters</em>.
4457 * Returns a new method handle which saves away the bound arguments.
4458 * When it is invoked, it receives arguments for any non-bound parameters,
4459 * binds the saved arguments to their corresponding parameters,
4460 * and calls the original target.
4461 * <p>
4462 * The type of the new method handle will drop the types for the bound
4463 * parameters from the original target type, since the new method handle
4464 * will no longer require those arguments to be supplied by its callers.
4465 * <p>
4466 * Each given argument object must match the corresponding bound parameter type.
4467 * If a bound parameter type is a primitive, the argument object
4468 * must be a wrapper, and will be unboxed to produce the primitive value.
4469 * <p>
4470 * The {@code pos} argument selects which parameters are to be bound.
4471 * It may range between zero and <i>N-L</i> (inclusively),
4472 * where <i>N</i> is the arity of the target method handle
4473 * and <i>L</i> is the length of the values array.
4474 * <p>
4475 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4476 * variable-arity method handle}, even if the original target method handle was.
4477 * @param target the method handle to invoke after the argument is inserted
4478 * @param pos where to insert the argument (zero for the first)
4479 * @param values the series of arguments to insert
4480 * @return a method handle which inserts an additional argument,
4481 * before calling the original method handle
4482 * @throws NullPointerException if the target or the {@code values} array is null
4483 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
4484 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4485 * is the length of the values array.
4486 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4487 * type.
4488 * @see MethodHandle#bindTo
4489 */
4490 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4491 int insCount = values.length;
4492 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4493 if (insCount == 0) return target;
4494 BoundMethodHandle result = target.rebind();
4495 for (int i = 0; i < insCount; i++) {
4496 Object value = values[i];
4497 Class<?> ptype = ptypes[pos+i];
4498 if (ptype.isPrimitive()) {
4499 result = insertArgumentPrimitive(result, pos, ptype, value);
4500 } else {
4501 value = ptype.cast(value); // throw CCE if needed
4502 result = result.bindArgumentL(pos, value);
4503 }
4504 }
4505 return result;
4506 }
4507
4508 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4509 Class<?> ptype, Object value) {
4510 Wrapper w = Wrapper.forPrimitiveType(ptype);
4511 // perform unboxing and/or primitive conversion
4512 value = w.convert(value, ptype);
4513 switch (w) {
4514 case INT: return result.bindArgumentI(pos, (int)value);
4515 case LONG: return result.bindArgumentJ(pos, (long)value);
4516 case FLOAT: return result.bindArgumentF(pos, (float)value);
4517 case DOUBLE: return result.bindArgumentD(pos, (double)value);
4518 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
4519 }
4520 }
4521
4522 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
4523 MethodType oldType = target.type();
4524 int outargs = oldType.parameterCount();
4525 int inargs = outargs - insCount;
4526 if (inargs < 0)
4527 throw newIllegalArgumentException("too many values to insert");
4528 if (pos < 0 || pos > inargs)
4529 throw newIllegalArgumentException("no argument type to append");
4530 return oldType.ptypes();
4531 }
4532
4533 /**
4534 * Produces a method handle which will discard some dummy arguments
4535 * before calling some other specified <i>target</i> method handle.
4536 * The type of the new method handle will be the same as the target's type,
4537 * except it will also include the dummy argument types,
4538 * at some given position.
4539 * <p>
4540 * The {@code pos} argument may range between zero and <i>N</i>,
4541 * where <i>N</i> is the arity of the target.
4542 * If {@code pos} is zero, the dummy arguments will precede
4543 * the target's real arguments; if {@code pos} is <i>N</i>
4544 * they will come after.
4545 * <p>
4546 * <b>Example:</b>
4547 * <blockquote><pre>{@code
4548 import static java.lang.invoke.MethodHandles.*;
4549 import static java.lang.invoke.MethodType.*;
4550 ...
4551 MethodHandle cat = lookup().findVirtual(String.class,
4552 "concat", methodType(String.class, String.class));
4553 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4554 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
4555 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
4556 assertEquals(bigType, d0.type());
4557 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
4558 * }</pre></blockquote>
4559 * <p>
4560 * This method is also equivalent to the following code:
4561 * <blockquote><pre>
4562 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
4563 * </pre></blockquote>
4564 * @param target the method handle to invoke after the arguments are dropped
4565 * @param pos position of first argument to drop (zero for the leftmost)
4566 * @param valueTypes the type(s) of the argument(s) to drop
4567 * @return a method handle which drops arguments of the given types,
4568 * before calling the original method handle
4569 * @throws NullPointerException if the target is null,
4570 * or if the {@code valueTypes} list or any of its elements is null
4571 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4572 * or if {@code pos} is negative or greater than the arity of the target,
4573 * or if the new method handle's type would have too many parameters
4574 */
4575 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4576 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
4577 }
4578
4579 private static List<Class<?>> copyTypes(Object[] array) {
4580 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
4581 }
4582
4583 private static MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4584 MethodType oldType = target.type(); // get NPE
4585 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
4586 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
4587 if (dropped == 0) return target;
4588 BoundMethodHandle result = target.rebind();
4589 LambdaForm lform = result.form;
4590 int insertFormArg = 1 + pos;
4591 for (Class<?> ptype : valueTypes) {
4592 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
4593 }
4594 result = result.copyWith(newType, lform);
4595 return result;
4596 }
4597
4598 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
4599 int dropped = valueTypes.size();
4600 MethodType.checkSlotCount(dropped);
4601 int outargs = oldType.parameterCount();
4602 int inargs = outargs + dropped;
4603 if (pos < 0 || pos > outargs)
4604 throw newIllegalArgumentException("no argument type to remove"
4605 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
4606 );
4607 return dropped;
4608 }
4609
4610 /**
4611 * Produces a method handle which will discard some dummy arguments
4612 * before calling some other specified <i>target</i> method handle.
4613 * The type of the new method handle will be the same as the target's type,
4614 * except it will also include the dummy argument types,
4615 * at some given position.
4616 * <p>
4617 * The {@code pos} argument may range between zero and <i>N</i>,
4618 * where <i>N</i> is the arity of the target.
4619 * If {@code pos} is zero, the dummy arguments will precede
4620 * the target's real arguments; if {@code pos} is <i>N</i>
4621 * they will come after.
4622 * @apiNote
4623 * <blockquote><pre>{@code
4624 import static java.lang.invoke.MethodHandles.*;
4625 import static java.lang.invoke.MethodType.*;
4626 ...
4627 MethodHandle cat = lookup().findVirtual(String.class,
4628 "concat", methodType(String.class, String.class));
4629 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4630 MethodHandle d0 = dropArguments(cat, 0, String.class);
4631 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
4632 MethodHandle d1 = dropArguments(cat, 1, String.class);
4633 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4634 MethodHandle d2 = dropArguments(cat, 2, String.class);
4635 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4636 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4637 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4638 * }</pre></blockquote>
4639 * <p>
4640 * This method is also equivalent to the following code:
4641 * <blockquote><pre>
4642 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4643 * </pre></blockquote>
4644 * @param target the method handle to invoke after the arguments are dropped
4645 * @param pos position of first argument to drop (zero for the leftmost)
4646 * @param valueTypes the type(s) of the argument(s) to drop
4647 * @return a method handle which drops arguments of the given types,
4648 * before calling the original method handle
4649 * @throws NullPointerException if the target is null,
4650 * or if the {@code valueTypes} array or any of its elements is null
4651 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4652 * or if {@code pos} is negative or greater than the arity of the target,
4653 * or if the new method handle's type would have
4654 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4655 */
4656 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4657 return dropArguments0(target, pos, copyTypes(valueTypes));
4658 }
4659
4660 // private version which allows caller some freedom with error handling
4661 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4662 boolean nullOnFailure) {
4663 newTypes = copyTypes(newTypes.toArray());
4664 List<Class<?>> oldTypes = target.type().parameterList();
4665 int match = oldTypes.size();
4666 if (skip != 0) {
4667 if (skip < 0 || skip > match) {
4668 throw newIllegalArgumentException("illegal skip", skip, target);
4669 }
4670 oldTypes = oldTypes.subList(skip, match);
4671 match -= skip;
4672 }
4673 List<Class<?>> addTypes = newTypes;
4674 int add = addTypes.size();
4675 if (pos != 0) {
4676 if (pos < 0 || pos > add) {
4677 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4678 }
4679 addTypes = addTypes.subList(pos, add);
4680 add -= pos;
4681 assert(addTypes.size() == add);
4682 }
4683 // Do not add types which already match the existing arguments.
4684 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4685 if (nullOnFailure) {
4686 return null;
4687 }
4688 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
4689 }
4690 addTypes = addTypes.subList(match, add);
4691 add -= match;
4692 assert(addTypes.size() == add);
4693 // newTypes: ( P*[pos], M*[match], A*[add] )
4694 // target: ( S*[skip], M*[match] )
4695 MethodHandle adapter = target;
4696 if (add > 0) {
4697 adapter = dropArguments0(adapter, skip+ match, addTypes);
4698 }
4699 // adapter: (S*[skip], M*[match], A*[add] )
4700 if (pos > 0) {
4701 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
4702 }
4703 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
4704 return adapter;
4705 }
4706
4707 /**
4708 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
4709 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
4710 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
4711 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
4712 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
4713 * {@link #dropArguments(MethodHandle, int, Class[])}.
4714 * <p>
4715 * The resulting handle will have the same return type as the target handle.
4716 * <p>
4717 * In more formal terms, assume these two type lists:<ul>
4718 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
4719 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
4720 * {@code newTypes}.
4721 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
4722 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
4723 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
4724 * sub-list.
4725 * </ul>
4726 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
4727 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
4728 * {@link #dropArguments(MethodHandle, int, Class[])}.
4729 *
4730 * @apiNote
4731 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
4732 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
4733 * <blockquote><pre>{@code
4734 import static java.lang.invoke.MethodHandles.*;
4735 import static java.lang.invoke.MethodType.*;
4736 ...
4737 ...
4738 MethodHandle h0 = constant(boolean.class, true);
4739 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
4740 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
4741 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
4742 if (h1.type().parameterCount() < h2.type().parameterCount())
4743 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
4744 else
4745 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
4746 MethodHandle h3 = guardWithTest(h0, h1, h2);
4747 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
4748 * }</pre></blockquote>
4749 * @param target the method handle to adapt
4750 * @param skip number of targets parameters to disregard (they will be unchanged)
4751 * @param newTypes the list of types to match {@code target}'s parameter type list to
4752 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
4753 * @return a possibly adapted method handle
4754 * @throws NullPointerException if either argument is null
4755 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
4756 * or if {@code skip} is negative or greater than the arity of the target,
4757 * or if {@code pos} is negative or greater than the newTypes list size,
4758 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
4759 * {@code pos}.
4760 * @since 9
4761 */
4762 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
4763 Objects.requireNonNull(target);
4764 Objects.requireNonNull(newTypes);
4765 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
4766 }
4767
4768 /**
4769 * Adapts a target method handle by pre-processing
4770 * one or more of its arguments, each with its own unary filter function,
4771 * and then calling the target with each pre-processed argument
4772 * replaced by the result of its corresponding filter function.
4773 * <p>
4774 * The pre-processing is performed by one or more method handles,
4775 * specified in the elements of the {@code filters} array.
4776 * The first element of the filter array corresponds to the {@code pos}
4777 * argument of the target, and so on in sequence.
4778 * The filter functions are invoked in left to right order.
4779 * <p>
4780 * Null arguments in the array are treated as identity functions,
4781 * and the corresponding arguments left unchanged.
4782 * (If there are no non-null elements in the array, the original target is returned.)
4783 * Each filter is applied to the corresponding argument of the adapter.
4784 * <p>
4785 * If a filter {@code F} applies to the {@code N}th argument of
4786 * the target, then {@code F} must be a method handle which
4787 * takes exactly one argument. The type of {@code F}'s sole argument
4788 * replaces the corresponding argument type of the target
4789 * in the resulting adapted method handle.
4790 * The return type of {@code F} must be identical to the corresponding
4791 * parameter type of the target.
4792 * <p>
4793 * It is an error if there are elements of {@code filters}
4794 * (null or not)
4795 * which do not correspond to argument positions in the target.
4796 * <p><b>Example:</b>
4797 * <blockquote><pre>{@code
4798 import static java.lang.invoke.MethodHandles.*;
4799 import static java.lang.invoke.MethodType.*;
4800 ...
4801 MethodHandle cat = lookup().findVirtual(String.class,
4802 "concat", methodType(String.class, String.class));
4803 MethodHandle upcase = lookup().findVirtual(String.class,
4804 "toUpperCase", methodType(String.class));
4805 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4806 MethodHandle f0 = filterArguments(cat, 0, upcase);
4807 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
4808 MethodHandle f1 = filterArguments(cat, 1, upcase);
4809 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
4810 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
4811 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
4812 * }</pre></blockquote>
4813 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4814 * denotes the return type of both the {@code target} and resulting adapter.
4815 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
4816 * of the parameters and arguments that precede and follow the filter position
4817 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
4818 * values of the filtered parameters and arguments; they also represent the
4819 * return types of the {@code filter[i]} handles. The latter accept arguments
4820 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
4821 * the resulting adapter.
4822 * <blockquote><pre>{@code
4823 * T target(P... p, A[i]... a[i], B... b);
4824 * A[i] filter[i](V[i]);
4825 * T adapter(P... p, V[i]... v[i], B... b) {
4826 * return target(p..., filter[i](v[i])..., b...);
4827 * }
4828 * }</pre></blockquote>
4829 * <p>
4830 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4831 * variable-arity method handle}, even if the original target method handle was.
4832 *
4833 * @param target the method handle to invoke after arguments are filtered
4834 * @param pos the position of the first argument to filter
4835 * @param filters method handles to call initially on filtered arguments
4836 * @return method handle which incorporates the specified argument filtering logic
4837 * @throws NullPointerException if the target is null
4838 * or if the {@code filters} array is null
4839 * @throws IllegalArgumentException if a non-null element of {@code filters}
4840 * does not match a corresponding argument type of target as described above,
4841 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
4842 * or if the resulting method handle's type would have
4843 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4844 */
4845 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
4846 // In method types arguments start at index 0, while the LF
4847 // editor have the MH receiver at position 0 - adjust appropriately.
4848 final int MH_RECEIVER_OFFSET = 1;
4849 filterArgumentsCheckArity(target, pos, filters);
4850 MethodHandle adapter = target;
4851
4852 // keep track of currently matched filters, as to optimize repeated filters
4853 int index = 0;
4854 int[] positions = new int[filters.length];
4855 MethodHandle filter = null;
4856
4857 // process filters in reverse order so that the invocation of
4858 // the resulting adapter will invoke the filters in left-to-right order
4859 for (int i = filters.length - 1; i >= 0; --i) {
4860 MethodHandle newFilter = filters[i];
4861 if (newFilter == null) continue; // ignore null elements of filters
4862
4863 // flush changes on update
4864 if (filter != newFilter) {
4865 if (filter != null) {
4866 if (index > 1) {
4867 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4868 } else {
4869 adapter = filterArgument(adapter, positions[0] - 1, filter);
4870 }
4871 }
4872 filter = newFilter;
4873 index = 0;
4874 }
4875
4876 filterArgumentChecks(target, pos + i, newFilter);
4877 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
4878 }
4879 if (index > 1) {
4880 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4881 } else if (index == 1) {
4882 adapter = filterArgument(adapter, positions[0] - 1, filter);
4883 }
4884 return adapter;
4885 }
4886
4887 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
4888 MethodType targetType = adapter.type();
4889 MethodType filterType = filter.type();
4890 BoundMethodHandle result = adapter.rebind();
4891 Class<?> newParamType = filterType.parameterType(0);
4892
4893 Class<?>[] ptypes = targetType.ptypes().clone();
4894 for (int pos : positions) {
4895 ptypes[pos - 1] = newParamType;
4896 }
4897 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
4898
4899 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
4900 return result.copyWithExtendL(newType, lform, filter);
4901 }
4902
4903 /*non-public*/
4904 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
4905 filterArgumentChecks(target, pos, filter);
4906 MethodType targetType = target.type();
4907 MethodType filterType = filter.type();
4908 BoundMethodHandle result = target.rebind();
4909 Class<?> newParamType = filterType.parameterType(0);
4910 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
4911 MethodType newType = targetType.changeParameterType(pos, newParamType);
4912 result = result.copyWithExtendL(newType, lform, filter);
4913 return result;
4914 }
4915
4916 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
4917 MethodType targetType = target.type();
4918 int maxPos = targetType.parameterCount();
4919 if (pos + filters.length > maxPos)
4920 throw newIllegalArgumentException("too many filters");
4921 }
4922
4923 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4924 MethodType targetType = target.type();
4925 MethodType filterType = filter.type();
4926 if (filterType.parameterCount() != 1
4927 || filterType.returnType() != targetType.parameterType(pos))
4928 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4929 }
4930
4931 /**
4932 * Adapts a target method handle by pre-processing
4933 * a sub-sequence of its arguments with a filter (another method handle).
4934 * The pre-processed arguments are replaced by the result (if any) of the
4935 * filter function.
4936 * The target is then called on the modified (usually shortened) argument list.
4937 * <p>
4938 * If the filter returns a value, the target must accept that value as
4939 * its argument in position {@code pos}, preceded and/or followed by
4940 * any arguments not passed to the filter.
4941 * If the filter returns void, the target must accept all arguments
4942 * not passed to the filter.
4943 * No arguments are reordered, and a result returned from the filter
4944 * replaces (in order) the whole subsequence of arguments originally
4945 * passed to the adapter.
4946 * <p>
4947 * The argument types (if any) of the filter
4948 * replace zero or one argument types of the target, at position {@code pos},
4949 * in the resulting adapted method handle.
4950 * The return type of the filter (if any) must be identical to the
4951 * argument type of the target at position {@code pos}, and that target argument
4952 * is supplied by the return value of the filter.
4953 * <p>
4954 * In all cases, {@code pos} must be greater than or equal to zero, and
4955 * {@code pos} must also be less than or equal to the target's arity.
4956 * <p><b>Example:</b>
4957 * <blockquote><pre>{@code
4958 import static java.lang.invoke.MethodHandles.*;
4959 import static java.lang.invoke.MethodType.*;
4960 ...
4961 MethodHandle deepToString = publicLookup()
4962 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
4963
4964 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
4965 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
4966
4967 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
4968 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
4969
4970 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
4971 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
4972 assertEquals("[top, [up, down], strange]",
4973 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
4974
4975 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
4976 assertEquals("[top, [up, down], [strange]]",
4977 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
4978
4979 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4980 assertEquals("[top, [[up, down, strange], charm], bottom]",
4981 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4982 * }</pre></blockquote>
4983 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4984 * represents the return type of the {@code target} and resulting adapter.
4985 * {@code V}/{@code v} stand for the return type and value of the
4986 * {@code filter}, which are also found in the signature and arguments of
4987 * the {@code target}, respectively, unless {@code V} is {@code void}.
4988 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4989 * and values preceding and following the collection position, {@code pos},
4990 * in the {@code target}'s signature. They also turn up in the resulting
4991 * adapter's signature and arguments, where they surround
4992 * {@code B}/{@code b}, which represent the parameter types and arguments
4993 * to the {@code filter} (if any).
4994 * <blockquote><pre>{@code
4995 * T target(A...,V,C...);
4996 * V filter(B...);
4997 * T adapter(A... a,B... b,C... c) {
4998 * V v = filter(b...);
4999 * return target(a...,v,c...);
5000 * }
5001 * // and if the filter has no arguments:
5002 * T target2(A...,V,C...);
5003 * V filter2();
5004 * T adapter2(A... a,C... c) {
5005 * V v = filter2();
5006 * return target2(a...,v,c...);
5007 * }
5008 * // and if the filter has a void return:
5009 * T target3(A...,C...);
5010 * void filter3(B...);
5011 * T adapter3(A... a,B... b,C... c) {
5012 * filter3(b...);
5013 * return target3(a...,c...);
5014 * }
5015 * }</pre></blockquote>
5016 * <p>
5017 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5018 * one which first "folds" the affected arguments, and then drops them, in separate
5019 * steps as follows:
5020 * <blockquote><pre>{@code
5021 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5022 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5023 * }</pre></blockquote>
5024 * If the target method handle consumes no arguments besides than the result
5025 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5026 * is equivalent to {@code filterReturnValue(coll, mh)}.
5027 * If the filter method handle {@code coll} consumes one argument and produces
5028 * a non-void result, then {@code collectArguments(mh, N, coll)}
5029 * is equivalent to {@code filterArguments(mh, N, coll)}.
5030 * Other equivalences are possible but would require argument permutation.
5031 * <p>
5032 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5033 * variable-arity method handle}, even if the original target method handle was.
5034 *
5035 * @param target the method handle to invoke after filtering the subsequence of arguments
5036 * @param pos the position of the first adapter argument to pass to the filter,
5037 * and/or the target argument which receives the result of the filter
5038 * @param filter method handle to call on the subsequence of arguments
5039 * @return method handle which incorporates the specified argument subsequence filtering logic
5040 * @throws NullPointerException if either argument is null
5041 * @throws IllegalArgumentException if the return type of {@code filter}
5042 * is non-void and is not the same as the {@code pos} argument of the target,
5043 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5044 * or if the resulting method handle's type would have
5045 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5046 * @see MethodHandles#foldArguments
5047 * @see MethodHandles#filterArguments
5048 * @see MethodHandles#filterReturnValue
5049 */
5050 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5051 MethodType newType = collectArgumentsChecks(target, pos, filter);
5052 MethodType collectorType = filter.type();
5053 BoundMethodHandle result = target.rebind();
5054 LambdaForm lform;
5055 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
5056 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
5057 if (lform != null) {
5058 return result.copyWith(newType, lform);
5059 }
5060 }
5061 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5062 return result.copyWithExtendL(newType, lform, filter);
5063 }
5064
5065 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5066 MethodType targetType = target.type();
5067 MethodType filterType = filter.type();
5068 Class<?> rtype = filterType.returnType();
5069 List<Class<?>> filterArgs = filterType.parameterList();
5070 if (rtype == void.class) {
5071 return targetType.insertParameterTypes(pos, filterArgs);
5072 }
5073 if (rtype != targetType.parameterType(pos)) {
5074 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5075 }
5076 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
5077 }
5078
5079 /**
5080 * Adapts a target method handle by post-processing
5081 * its return value (if any) with a filter (another method handle).
5082 * The result of the filter is returned from the adapter.
5083 * <p>
5084 * If the target returns a value, the filter must accept that value as
5085 * its only argument.
5086 * If the target returns void, the filter must accept no arguments.
5087 * <p>
5088 * The return type of the filter
5089 * replaces the return type of the target
5090 * in the resulting adapted method handle.
5091 * The argument type of the filter (if any) must be identical to the
5092 * return type of the target.
5093 * <p><b>Example:</b>
5094 * <blockquote><pre>{@code
5095 import static java.lang.invoke.MethodHandles.*;
5096 import static java.lang.invoke.MethodType.*;
5097 ...
5098 MethodHandle cat = lookup().findVirtual(String.class,
5099 "concat", methodType(String.class, String.class));
5100 MethodHandle length = lookup().findVirtual(String.class,
5101 "length", methodType(int.class));
5102 System.out.println((String) cat.invokeExact("x", "y")); // xy
5103 MethodHandle f0 = filterReturnValue(cat, length);
5104 System.out.println((int) f0.invokeExact("x", "y")); // 2
5105 * }</pre></blockquote>
5106 * <p>Here is pseudocode for the resulting adapter. In the code,
5107 * {@code T}/{@code t} represent the result type and value of the
5108 * {@code target}; {@code V}, the result type of the {@code filter}; and
5109 * {@code A}/{@code a}, the types and values of the parameters and arguments
5110 * of the {@code target} as well as the resulting adapter.
5111 * <blockquote><pre>{@code
5112 * T target(A...);
5113 * V filter(T);
5114 * V adapter(A... a) {
5115 * T t = target(a...);
5116 * return filter(t);
5117 * }
5118 * // and if the target has a void return:
5119 * void target2(A...);
5120 * V filter2();
5121 * V adapter2(A... a) {
5122 * target2(a...);
5123 * return filter2();
5124 * }
5125 * // and if the filter has a void return:
5126 * T target3(A...);
5127 * void filter3(V);
5128 * void adapter3(A... a) {
5129 * T t = target3(a...);
5130 * filter3(t);
5131 * }
5132 * }</pre></blockquote>
5133 * <p>
5134 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5135 * variable-arity method handle}, even if the original target method handle was.
5136 * @param target the method handle to invoke before filtering the return value
5137 * @param filter method handle to call on the return value
5138 * @return method handle which incorporates the specified return value filtering logic
5139 * @throws NullPointerException if either argument is null
5140 * @throws IllegalArgumentException if the argument list of {@code filter}
5141 * does not match the return type of target as described above
5142 */
5143 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5144 MethodType targetType = target.type();
5145 MethodType filterType = filter.type();
5146 filterReturnValueChecks(targetType, filterType);
5147 BoundMethodHandle result = target.rebind();
5148 BasicType rtype = BasicType.basicType(filterType.returnType());
5149 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5150 MethodType newType = targetType.changeReturnType(filterType.returnType());
5151 result = result.copyWithExtendL(newType, lform, filter);
5152 return result;
5153 }
5154
5155 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5156 Class<?> rtype = targetType.returnType();
5157 int filterValues = filterType.parameterCount();
5158 if (filterValues == 0
5159 ? (rtype != void.class)
5160 : (rtype != filterType.parameterType(0) || filterValues != 1))
5161 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5162 }
5163
5164 /**
5165 * Adapts a target method handle by pre-processing
5166 * some of its arguments, and then calling the target with
5167 * the result of the pre-processing, inserted into the original
5168 * sequence of arguments.
5169 * <p>
5170 * The pre-processing is performed by {@code combiner}, a second method handle.
5171 * Of the arguments passed to the adapter, the first {@code N} arguments
5172 * are copied to the combiner, which is then called.
5173 * (Here, {@code N} is defined as the parameter count of the combiner.)
5174 * After this, control passes to the target, with any result
5175 * from the combiner inserted before the original {@code N} incoming
5176 * arguments.
5177 * <p>
5178 * If the combiner returns a value, the first parameter type of the target
5179 * must be identical with the return type of the combiner, and the next
5180 * {@code N} parameter types of the target must exactly match the parameters
5181 * of the combiner.
5182 * <p>
5183 * If the combiner has a void return, no result will be inserted,
5184 * and the first {@code N} parameter types of the target
5185 * must exactly match the parameters of the combiner.
5186 * <p>
5187 * The resulting adapter is the same type as the target, except that the
5188 * first parameter type is dropped,
5189 * if it corresponds to the result of the combiner.
5190 * <p>
5191 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5192 * that either the combiner or the target does not wish to receive.
5193 * If some of the incoming arguments are destined only for the combiner,
5194 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5195 * arguments will not need to be live on the stack on entry to the
5196 * target.)
5197 * <p><b>Example:</b>
5198 * <blockquote><pre>{@code
5199 import static java.lang.invoke.MethodHandles.*;
5200 import static java.lang.invoke.MethodType.*;
5201 ...
5202 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5203 "println", methodType(void.class, String.class))
5204 .bindTo(System.out);
5205 MethodHandle cat = lookup().findVirtual(String.class,
5206 "concat", methodType(String.class, String.class));
5207 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5208 MethodHandle catTrace = foldArguments(cat, trace);
5209 // also prints "boo":
5210 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5211 * }</pre></blockquote>
5212 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5213 * represents the result type of the {@code target} and resulting adapter.
5214 * {@code V}/{@code v} represent the type and value of the parameter and argument
5215 * of {@code target} that precedes the folding position; {@code V} also is
5216 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5217 * types and values of the {@code N} parameters and arguments at the folding
5218 * position. {@code B}/{@code b} represent the types and values of the
5219 * {@code target} parameters and arguments that follow the folded parameters
5220 * and arguments.
5221 * <blockquote><pre>{@code
5222 * // there are N arguments in A...
5223 * T target(V, A[N]..., B...);
5224 * V combiner(A...);
5225 * T adapter(A... a, B... b) {
5226 * V v = combiner(a...);
5227 * return target(v, a..., b...);
5228 * }
5229 * // and if the combiner has a void return:
5230 * T target2(A[N]..., B...);
5231 * void combiner2(A...);
5232 * T adapter2(A... a, B... b) {
5233 * combiner2(a...);
5234 * return target2(a..., b...);
5235 * }
5236 * }</pre></blockquote>
5237 * <p>
5238 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5239 * variable-arity method handle}, even if the original target method handle was.
5240 * @param target the method handle to invoke after arguments are combined
5241 * @param combiner method handle to call initially on the incoming arguments
5242 * @return method handle which incorporates the specified argument folding logic
5243 * @throws NullPointerException if either argument is null
5244 * @throws IllegalArgumentException if {@code combiner}'s return type
5245 * is non-void and not the same as the first argument type of
5246 * the target, or if the initial {@code N} argument types
5247 * of the target
5248 * (skipping one matching the {@code combiner}'s return type)
5249 * are not identical with the argument types of {@code combiner}
5250 */
5251 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5252 return foldArguments(target, 0, combiner);
5253 }
5254
5255 /**
5256 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5257 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5258 * before the folded arguments.
5259 * <p>
5260 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5261 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5262 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5263 * 0.
5264 *
5265 * @apiNote Example:
5266 * <blockquote><pre>{@code
5267 import static java.lang.invoke.MethodHandles.*;
5268 import static java.lang.invoke.MethodType.*;
5269 ...
5270 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5271 "println", methodType(void.class, String.class))
5272 .bindTo(System.out);
5273 MethodHandle cat = lookup().findVirtual(String.class,
5274 "concat", methodType(String.class, String.class));
5275 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5276 MethodHandle catTrace = foldArguments(cat, 1, trace);
5277 // also prints "jum":
5278 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5279 * }</pre></blockquote>
5280 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5281 * represents the result type of the {@code target} and resulting adapter.
5282 * {@code V}/{@code v} represent the type and value of the parameter and argument
5283 * of {@code target} that precedes the folding position; {@code V} also is
5284 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5285 * types and values of the {@code N} parameters and arguments at the folding
5286 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5287 * and values of the {@code target} parameters and arguments that precede and
5288 * follow the folded parameters and arguments starting at {@code pos},
5289 * respectively.
5290 * <blockquote><pre>{@code
5291 * // there are N arguments in A...
5292 * T target(Z..., V, A[N]..., B...);
5293 * V combiner(A...);
5294 * T adapter(Z... z, A... a, B... b) {
5295 * V v = combiner(a...);
5296 * return target(z..., v, a..., b...);
5297 * }
5298 * // and if the combiner has a void return:
5299 * T target2(Z..., A[N]..., B...);
5300 * void combiner2(A...);
5301 * T adapter2(Z... z, A... a, B... b) {
5302 * combiner2(a...);
5303 * return target2(z..., a..., b...);
5304 * }
5305 * }</pre></blockquote>
5306 * <p>
5307 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5308 * variable-arity method handle}, even if the original target method handle was.
5309 *
5310 * @param target the method handle to invoke after arguments are combined
5311 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5312 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5313 * @param combiner method handle to call initially on the incoming arguments
5314 * @return method handle which incorporates the specified argument folding logic
5315 * @throws NullPointerException if either argument is null
5316 * @throws IllegalArgumentException if either of the following two conditions holds:
5317 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5318 * {@code pos} of the target signature;
5319 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5320 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5321 *
5322 * @see #foldArguments(MethodHandle, MethodHandle)
5323 * @since 9
5324 */
5325 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5326 MethodType targetType = target.type();
5327 MethodType combinerType = combiner.type();
5328 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5329 BoundMethodHandle result = target.rebind();
5330 boolean dropResult = rtype == void.class;
5331 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5332 MethodType newType = targetType;
5333 if (!dropResult) {
5334 newType = newType.dropParameterTypes(pos, pos + 1);
5335 }
5336 result = result.copyWithExtendL(newType, lform, combiner);
5337 return result;
5338 }
5339
5340 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5341 int foldArgs = combinerType.parameterCount();
5342 Class<?> rtype = combinerType.returnType();
5343 int foldVals = rtype == void.class ? 0 : 1;
5344 int afterInsertPos = foldPos + foldVals;
5345 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5346 if (ok) {
5347 for (int i = 0; i < foldArgs; i++) {
5348 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5349 ok = false;
5350 break;
5351 }
5352 }
5353 }
5354 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5355 ok = false;
5356 if (!ok)
5357 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5358 return rtype;
5359 }
5360
5361 /**
5362 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5363 * of the pre-processing replacing the argument at the given position.
5364 *
5365 * @param target the method handle to invoke after arguments are combined
5366 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5367 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5368 * @param combiner method handle to call initially on the incoming arguments
5369 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5370 * @return method handle which incorporates the specified argument folding logic
5371 * @throws NullPointerException if either argument is null
5372 * @throws IllegalArgumentException if either of the following two conditions holds:
5373 * (1) {@code combiner}'s return type is not the same as the argument type at position
5374 * {@code pos} of the target signature;
5375 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5376 * not identical with the argument types of {@code combiner}.
5377 */
5378 /*non-public*/
5379 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5380 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5381 }
5382
5383 /**
5384 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5385 * the pre-processing inserted into the original sequence of arguments at the given position.
5386 *
5387 * @param target the method handle to invoke after arguments are combined
5388 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5389 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5390 * @param combiner method handle to call initially on the incoming arguments
5391 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5392 * @return method handle which incorporates the specified argument folding logic
5393 * @throws NullPointerException if either argument is null
5394 * @throws IllegalArgumentException if either of the following two conditions holds:
5395 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5396 * {@code pos} of the target signature;
5397 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5398 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5399 * with the argument types of {@code combiner}.
5400 */
5401 /*non-public*/
5402 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5403 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5404 }
5405
5406 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5407 MethodType targetType = target.type();
5408 MethodType combinerType = combiner.type();
5409 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5410 BoundMethodHandle result = target.rebind();
5411
5412 MethodType newType = targetType;
5413 LambdaForm lform;
5414 if (filter) {
5415 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5416 } else {
5417 boolean dropResult = rtype == void.class;
5418 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5419 if (!dropResult) {
5420 newType = newType.dropParameterTypes(position, position + 1);
5421 }
5422 }
5423 result = result.copyWithExtendL(newType, lform, combiner);
5424 return result;
5425 }
5426
5427 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5428 int combinerArgs = combinerType.parameterCount();
5429 if (argPos.length != combinerArgs) {
5430 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5431 }
5432 Class<?> rtype = combinerType.returnType();
5433
5434 for (int i = 0; i < combinerArgs; i++) {
5435 int arg = argPos[i];
5436 if (arg < 0 || arg > targetType.parameterCount()) {
5437 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5438 }
5439 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5440 throw newIllegalArgumentException("target argument type at position " + arg
5441 + " must match combiner argument type at index " + i + ": " + targetType
5442 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5443 }
5444 }
5445 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5446 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5447 }
5448 return rtype;
5449 }
5450
5451 /**
5452 * Makes a method handle which adapts a target method handle,
5453 * by guarding it with a test, a boolean-valued method handle.
5454 * If the guard fails, a fallback handle is called instead.
5455 * All three method handles must have the same corresponding
5456 * argument and return types, except that the return type
5457 * of the test must be boolean, and the test is allowed
5458 * to have fewer arguments than the other two method handles.
5459 * <p>
5460 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5461 * represents the uniform result type of the three involved handles;
5462 * {@code A}/{@code a}, the types and values of the {@code target}
5463 * parameters and arguments that are consumed by the {@code test}; and
5464 * {@code B}/{@code b}, those types and values of the {@code target}
5465 * parameters and arguments that are not consumed by the {@code test}.
5466 * <blockquote><pre>{@code
5467 * boolean test(A...);
5468 * T target(A...,B...);
5469 * T fallback(A...,B...);
5470 * T adapter(A... a,B... b) {
5471 * if (test(a...))
5472 * return target(a..., b...);
5473 * else
5474 * return fallback(a..., b...);
5475 * }
5476 * }</pre></blockquote>
5477 * Note that the test arguments ({@code a...} in the pseudocode) cannot
5478 * be modified by execution of the test, and so are passed unchanged
5479 * from the caller to the target or fallback as appropriate.
5480 * @param test method handle used for test, must return boolean
5481 * @param target method handle to call if test passes
5482 * @param fallback method handle to call if test fails
5483 * @return method handle which incorporates the specified if/then/else logic
5484 * @throws NullPointerException if any argument is null
5485 * @throws IllegalArgumentException if {@code test} does not return boolean,
5486 * or if all three method types do not match (with the return
5487 * type of {@code test} changed to match that of the target).
5488 */
5489 public static MethodHandle guardWithTest(MethodHandle test,
5490 MethodHandle target,
5491 MethodHandle fallback) {
5492 MethodType gtype = test.type();
5493 MethodType ttype = target.type();
5494 MethodType ftype = fallback.type();
5495 if (!ttype.equals(ftype))
5496 throw misMatchedTypes("target and fallback types", ttype, ftype);
5497 if (gtype.returnType() != boolean.class)
5498 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
5499 List<Class<?>> targs = ttype.parameterList();
5500 test = dropArgumentsToMatch(test, 0, targs, 0, true);
5501 if (test == null) {
5502 throw misMatchedTypes("target and test types", ttype, gtype);
5503 }
5504 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
5505 }
5506
5507 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
5508 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
5509 }
5510
5511 /**
5512 * Makes a method handle which adapts a target method handle,
5513 * by running it inside an exception handler.
5514 * If the target returns normally, the adapter returns that value.
5515 * If an exception matching the specified type is thrown, the fallback
5516 * handle is called instead on the exception, plus the original arguments.
5517 * <p>
5518 * The target and handler must have the same corresponding
5519 * argument and return types, except that handler may omit trailing arguments
5520 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
5521 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
5522 * <p>
5523 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5524 * represents the return type of the {@code target} and {@code handler},
5525 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
5526 * the types and values of arguments to the resulting handle consumed by
5527 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
5528 * resulting handle discarded by {@code handler}.
5529 * <blockquote><pre>{@code
5530 * T target(A..., B...);
5531 * T handler(ExType, A...);
5532 * T adapter(A... a, B... b) {
5533 * try {
5534 * return target(a..., b...);
5535 * } catch (ExType ex) {
5536 * return handler(ex, a...);
5537 * }
5538 * }
5539 * }</pre></blockquote>
5540 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5541 * be modified by execution of the target, and so are passed unchanged
5542 * from the caller to the handler, if the handler is invoked.
5543 * <p>
5544 * The target and handler must return the same type, even if the handler
5545 * always throws. (This might happen, for instance, because the handler
5546 * is simulating a {@code finally} clause).
5547 * To create such a throwing handler, compose the handler creation logic
5548 * with {@link #throwException throwException},
5549 * in order to create a method handle of the correct return type.
5550 * @param target method handle to call
5551 * @param exType the type of exception which the handler will catch
5552 * @param handler method handle to call if a matching exception is thrown
5553 * @return method handle which incorporates the specified try/catch logic
5554 * @throws NullPointerException if any argument is null
5555 * @throws IllegalArgumentException if {@code handler} does not accept
5556 * the given exception type, or if the method handle types do
5557 * not match in their return types and their
5558 * corresponding parameters
5559 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
5560 */
5561 public static MethodHandle catchException(MethodHandle target,
5562 Class<? extends Throwable> exType,
5563 MethodHandle handler) {
5564 MethodType ttype = target.type();
5565 MethodType htype = handler.type();
5566 if (!Throwable.class.isAssignableFrom(exType))
5567 throw new ClassCastException(exType.getName());
5568 if (htype.parameterCount() < 1 ||
5569 !htype.parameterType(0).isAssignableFrom(exType))
5570 throw newIllegalArgumentException("handler does not accept exception type "+exType);
5571 if (htype.returnType() != ttype.returnType())
5572 throw misMatchedTypes("target and handler return types", ttype, htype);
5573 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
5574 if (handler == null) {
5575 throw misMatchedTypes("target and handler types", ttype, htype);
5576 }
5577 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
5578 }
5579
5580 /**
5581 * Produces a method handle which will throw exceptions of the given {@code exType}.
5582 * The method handle will accept a single argument of {@code exType},
5583 * and immediately throw it as an exception.
5584 * The method type will nominally specify a return of {@code returnType}.
5585 * The return type may be anything convenient: It doesn't matter to the
5586 * method handle's behavior, since it will never return normally.
5587 * @param returnType the return type of the desired method handle
5588 * @param exType the parameter type of the desired method handle
5589 * @return method handle which can throw the given exceptions
5590 * @throws NullPointerException if either argument is null
5591 */
5592 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
5593 if (!Throwable.class.isAssignableFrom(exType))
5594 throw new ClassCastException(exType.getName());
5595 return MethodHandleImpl.throwException(methodType(returnType, exType));
5596 }
5597
5598 /**
5599 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
5600 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
5601 * delivers the loop's result, which is the return value of the resulting handle.
5602 * <p>
5603 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
5604 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
5605 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
5606 * terms of method handles, each clause will specify up to four independent actions:<ul>
5607 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
5608 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
5609 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
5610 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
5611 * </ul>
5612 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
5613 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
5614 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
5615 * <p>
5616 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
5617 * this case. See below for a detailed description.
5618 * <p>
5619 * <em>Parameters optional everywhere:</em>
5620 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
5621 * As an exception, the init functions cannot take any {@code v} parameters,
5622 * because those values are not yet computed when the init functions are executed.
5623 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
5624 * In fact, any clause function may take no arguments at all.
5625 * <p>
5626 * <em>Loop parameters:</em>
5627 * A clause function may take all the iteration variable values it is entitled to, in which case
5628 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
5629 * with their types and values notated as {@code (A...)} and {@code (a...)}.
5630 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
5631 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
5632 * init function is automatically a loop parameter {@code a}.)
5633 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
5634 * These loop parameters act as loop-invariant values visible across the whole loop.
5635 * <p>
5636 * <em>Parameters visible everywhere:</em>
5637 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
5638 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
5639 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
5640 * Most clause functions will not need all of this information, but they will be formally connected to it
5641 * as if by {@link #dropArguments}.
5642 * <a id="astar"></a>
5643 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
5644 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
5645 * In that notation, the general form of an init function parameter list
5646 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
5647 * <p>
5648 * <em>Checking clause structure:</em>
5649 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
5650 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
5651 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
5652 * met by the inputs to the loop combinator.
5653 * <p>
5654 * <em>Effectively identical sequences:</em>
5655 * <a id="effid"></a>
5656 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
5657 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
5658 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
5659 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
5660 * that longest list.
5661 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
5662 * and the same is true if more sequences of the form {@code (V... A*)} are added.
5663 * <p>
5664 * <em>Step 0: Determine clause structure.</em><ol type="a">
5665 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
5666 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
5667 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
5668 * four. Padding takes place by appending elements to the array.
5669 * <li>Clauses with all {@code null}s are disregarded.
5670 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
5671 * </ol>
5672 * <p>
5673 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
5674 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
5675 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
5676 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
5677 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
5678 * iteration variable type.
5679 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
5680 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
5681 * </ol>
5682 * <p>
5683 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
5684 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
5685 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
5686 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
5687 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
5688 * (These types will be checked in step 2, along with all the clause function types.)
5689 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
5690 * <li>All of the collected parameter lists must be effectively identical.
5691 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
5692 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
5693 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
5694 * the "internal parameter list".
5695 * </ul>
5696 * <p>
5697 * <em>Step 1C: Determine loop return type.</em><ol type="a">
5698 * <li>Examine fini function return types, disregarding omitted fini functions.
5699 * <li>If there are no fini functions, the loop return type is {@code void}.
5700 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
5701 * type.
5702 * </ol>
5703 * <p>
5704 * <em>Step 1D: Check other types.</em><ol type="a">
5705 * <li>There must be at least one non-omitted pred function.
5706 * <li>Every non-omitted pred function must have a {@code boolean} return type.
5707 * </ol>
5708 * <p>
5709 * <em>Step 2: Determine parameter lists.</em><ol type="a">
5710 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
5711 * <li>The parameter list for init functions will be adjusted to the external parameter list.
5712 * (Note that their parameter lists are already effectively identical to this list.)
5713 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
5714 * effectively identical to the internal parameter list {@code (V... A...)}.
5715 * </ol>
5716 * <p>
5717 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
5718 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
5719 * type.
5720 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
5721 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
5722 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
5723 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
5724 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
5725 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
5726 * loop return type.
5727 * </ol>
5728 * <p>
5729 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
5730 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
5731 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
5732 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
5733 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
5734 * pad out the end of the list.
5735 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
5736 * </ol>
5737 * <p>
5738 * <em>Final observations.</em><ol type="a">
5739 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
5740 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
5741 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
5742 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
5743 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
5744 * <li>Each pair of init and step functions agrees in their return type {@code V}.
5745 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
5746 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
5747 * </ol>
5748 * <p>
5749 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
5750 * <ul>
5751 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
5752 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
5753 * (Only one {@code Pn} has to be non-{@code null}.)
5754 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
5755 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
5756 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
5757 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
5758 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
5759 * the resulting loop handle's parameter types {@code (A...)}.
5760 * </ul>
5761 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
5762 * which is natural if most of the loop computation happens in the steps. For some loops,
5763 * the burden of computation might be heaviest in the pred functions, and so the pred functions
5764 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
5765 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
5766 * where the init functions will need the extra parameters. For such reasons, the rules for
5767 * determining these parameters are as symmetric as possible, across all clause parts.
5768 * In general, the loop parameters function as common invariant values across the whole
5769 * loop, while the iteration variables function as common variant values, or (if there is
5770 * no step function) as internal loop invariant temporaries.
5771 * <p>
5772 * <em>Loop execution.</em><ol type="a">
5773 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
5774 * every clause function. These locals are loop invariant.
5775 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
5776 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
5777 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
5778 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
5779 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
5780 * (in argument order).
5781 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
5782 * returns {@code false}.
5783 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
5784 * sequence {@code (v...)} of loop variables.
5785 * The updated value is immediately visible to all subsequent function calls.
5786 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
5787 * (of type {@code R}) is returned from the loop as a whole.
5788 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
5789 * except by throwing an exception.
5790 * </ol>
5791 * <p>
5792 * <em>Usage tips.</em>
5793 * <ul>
5794 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
5795 * sometimes a step function only needs to observe the current value of its own variable.
5796 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
5797 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
5798 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
5799 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
5800 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
5801 * <li>If some of the clause functions are virtual methods on an instance, the instance
5802 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
5803 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
5804 * will be the first iteration variable value, and it will be easy to use virtual
5805 * methods as clause parts, since all of them will take a leading instance reference matching that value.
5806 * </ul>
5807 * <p>
5808 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
5809 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
5810 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
5811 * <blockquote><pre>{@code
5812 * V... init...(A...);
5813 * boolean pred...(V..., A...);
5814 * V... step...(V..., A...);
5815 * R fini...(V..., A...);
5816 * R loop(A... a) {
5817 * V... v... = init...(a...);
5818 * for (;;) {
5819 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
5820 * v = s(v..., a...);
5821 * if (!p(v..., a...)) {
5822 * return f(v..., a...);
5823 * }
5824 * }
5825 * }
5826 * }
5827 * }</pre></blockquote>
5828 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
5829 * to their full length, even though individual clause functions may neglect to take them all.
5830 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
5831 *
5832 * @apiNote Example:
5833 * <blockquote><pre>{@code
5834 * // iterative implementation of the factorial function as a loop handle
5835 * static int one(int k) { return 1; }
5836 * static int inc(int i, int acc, int k) { return i + 1; }
5837 * static int mult(int i, int acc, int k) { return i * acc; }
5838 * static boolean pred(int i, int acc, int k) { return i < k; }
5839 * static int fin(int i, int acc, int k) { return acc; }
5840 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5841 * // null initializer for counter, should initialize to 0
5842 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5843 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5844 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5845 * assertEquals(120, loop.invoke(5));
5846 * }</pre></blockquote>
5847 * The same example, dropping arguments and using combinators:
5848 * <blockquote><pre>{@code
5849 * // simplified implementation of the factorial function as a loop handle
5850 * static int inc(int i) { return i + 1; } // drop acc, k
5851 * static int mult(int i, int acc) { return i * acc; } //drop k
5852 * static boolean cmp(int i, int k) { return i < k; }
5853 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
5854 * // null initializer for counter, should initialize to 0
5855 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5856 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
5857 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
5858 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5859 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5860 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5861 * assertEquals(720, loop.invoke(6));
5862 * }</pre></blockquote>
5863 * A similar example, using a helper object to hold a loop parameter:
5864 * <blockquote><pre>{@code
5865 * // instance-based implementation of the factorial function as a loop handle
5866 * static class FacLoop {
5867 * final int k;
5868 * FacLoop(int k) { this.k = k; }
5869 * int inc(int i) { return i + 1; }
5870 * int mult(int i, int acc) { return i * acc; }
5871 * boolean pred(int i) { return i < k; }
5872 * int fin(int i, int acc) { return acc; }
5873 * }
5874 * // assume MH_FacLoop is a handle to the constructor
5875 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5876 * // null initializer for counter, should initialize to 0
5877 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5878 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
5879 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5880 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5881 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
5882 * assertEquals(5040, loop.invoke(7));
5883 * }</pre></blockquote>
5884 *
5885 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
5886 *
5887 * @return a method handle embodying the looping behavior as defined by the arguments.
5888 *
5889 * @throws IllegalArgumentException in case any of the constraints described above is violated.
5890 *
5891 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
5892 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5893 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
5894 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
5895 * @since 9
5896 */
5897 public static MethodHandle loop(MethodHandle[]... clauses) {
5898 // Step 0: determine clause structure.
5899 loopChecks0(clauses);
5900
5901 List<MethodHandle> init = new ArrayList<>();
5902 List<MethodHandle> step = new ArrayList<>();
5903 List<MethodHandle> pred = new ArrayList<>();
5904 List<MethodHandle> fini = new ArrayList<>();
5905
5906 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
5907 init.add(clause[0]); // all clauses have at least length 1
5908 step.add(clause.length <= 1 ? null : clause[1]);
5909 pred.add(clause.length <= 2 ? null : clause[2]);
5910 fini.add(clause.length <= 3 ? null : clause[3]);
5911 });
5912
5913 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
5914 final int nclauses = init.size();
5915
5916 // Step 1A: determine iteration variables (V...).
5917 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
5918 for (int i = 0; i < nclauses; ++i) {
5919 MethodHandle in = init.get(i);
5920 MethodHandle st = step.get(i);
5921 if (in == null && st == null) {
5922 iterationVariableTypes.add(void.class);
5923 } else if (in != null && st != null) {
5924 loopChecks1a(i, in, st);
5925 iterationVariableTypes.add(in.type().returnType());
5926 } else {
5927 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
5928 }
5929 }
5930 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
5931 collect(Collectors.toList());
5932
5933 // Step 1B: determine loop parameters (A...).
5934 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
5935 loopChecks1b(init, commonSuffix);
5936
5937 // Step 1C: determine loop return type.
5938 // Step 1D: check other types.
5939 // local variable required here; see JDK-8223553
5940 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
5941 .map(MethodType::returnType);
5942 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
5943 loopChecks1cd(pred, fini, loopReturnType);
5944
5945 // Step 2: determine parameter lists.
5946 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
5947 commonParameterSequence.addAll(commonSuffix);
5948 loopChecks2(step, pred, fini, commonParameterSequence);
5949
5950 // Step 3: fill in omitted functions.
5951 for (int i = 0; i < nclauses; ++i) {
5952 Class<?> t = iterationVariableTypes.get(i);
5953 if (init.get(i) == null) {
5954 init.set(i, empty(methodType(t, commonSuffix)));
5955 }
5956 if (step.get(i) == null) {
5957 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
5958 }
5959 if (pred.get(i) == null) {
5960 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
5961 }
5962 if (fini.get(i) == null) {
5963 fini.set(i, empty(methodType(t, commonParameterSequence)));
5964 }
5965 }
5966
5967 // Step 4: fill in missing parameter types.
5968 // Also convert all handles to fixed-arity handles.
5969 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
5970 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
5971 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
5972 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
5973
5974 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
5975 allMatch(pl -> pl.equals(commonSuffix));
5976 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5977 allMatch(pl -> pl.equals(commonParameterSequence));
5978
5979 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5980 }
5981
5982 private static void loopChecks0(MethodHandle[][] clauses) {
5983 if (clauses == null || clauses.length == 0) {
5984 throw newIllegalArgumentException("null or no clauses passed");
5985 }
5986 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5987 throw newIllegalArgumentException("null clauses are not allowed");
5988 }
5989 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5990 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5991 }
5992 }
5993
5994 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5995 if (in.type().returnType() != st.type().returnType()) {
5996 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5997 st.type().returnType());
5998 }
5999 }
6000
6001 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6002 final List<Class<?>> empty = List.of();
6003 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
6004 // take only those that can contribute to a common suffix because they are longer than the prefix
6005 map(MethodHandle::type).
6006 filter(t -> t.parameterCount() > skipSize).
6007 map(MethodType::parameterList).
6008 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6009 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
6010 }
6011
6012 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
6013 final List<Class<?>> empty = List.of();
6014 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6015 }
6016
6017 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6018 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6019 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6020 return longestParameterList(Arrays.asList(longest1, longest2));
6021 }
6022
6023 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6024 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6025 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6026 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6027 " (common suffix: " + commonSuffix + ")");
6028 }
6029 }
6030
6031 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6032 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6033 anyMatch(t -> t != loopReturnType)) {
6034 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6035 loopReturnType + ")");
6036 }
6037
6038 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
6039 throw newIllegalArgumentException("no predicate found", pred);
6040 }
6041 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6042 anyMatch(t -> t != boolean.class)) {
6043 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6044 }
6045 }
6046
6047 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6048 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6049 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6050 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6051 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6052 }
6053 }
6054
6055 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6056 return hs.stream().map(h -> {
6057 int pc = h.type().parameterCount();
6058 int tpsize = targetParams.size();
6059 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
6060 }).collect(Collectors.toList());
6061 }
6062
6063 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6064 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
6065 }
6066
6067 /**
6068 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6069 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6070 * <p>
6071 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6072 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6073 * evaluates to {@code true}).
6074 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6075 * <p>
6076 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6077 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6078 * and updated with the value returned from its invocation. The result of loop execution will be
6079 * the final value of the additional loop-local variable (if present).
6080 * <p>
6081 * The following rules hold for these argument handles:<ul>
6082 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6083 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6084 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6085 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6086 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6087 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6088 * It will constrain the parameter lists of the other loop parts.
6089 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6090 * list {@code (A...)} is called the <em>external parameter list</em>.
6091 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6092 * additional state variable of the loop.
6093 * The body must both accept and return a value of this type {@code V}.
6094 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6095 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6096 * <a href="MethodHandles.html#effid">effectively identical</a>
6097 * to the external parameter list {@code (A...)}.
6098 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6099 * {@linkplain #empty default value}.
6100 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6101 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6102 * effectively identical to the internal parameter list.
6103 * </ul>
6104 * <p>
6105 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6106 * <li>The loop handle's result type is the result type {@code V} of the body.
6107 * <li>The loop handle's parameter types are the types {@code (A...)},
6108 * from the external parameter list.
6109 * </ul>
6110 * <p>
6111 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6112 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6113 * passed to the loop.
6114 * <blockquote><pre>{@code
6115 * V init(A...);
6116 * boolean pred(V, A...);
6117 * V body(V, A...);
6118 * V whileLoop(A... a...) {
6119 * V v = init(a...);
6120 * while (pred(v, a...)) {
6121 * v = body(v, a...);
6122 * }
6123 * return v;
6124 * }
6125 * }</pre></blockquote>
6126 *
6127 * @apiNote Example:
6128 * <blockquote><pre>{@code
6129 * // implement the zip function for lists as a loop handle
6130 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6131 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6132 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6133 * zip.add(a.next());
6134 * zip.add(b.next());
6135 * return zip;
6136 * }
6137 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6138 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6139 * List<String> a = Arrays.asList("a", "b", "c", "d");
6140 * List<String> b = Arrays.asList("e", "f", "g", "h");
6141 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6142 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6143 * }</pre></blockquote>
6144 *
6145 *
6146 * @apiNote The implementation of this method can be expressed as follows:
6147 * <blockquote><pre>{@code
6148 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6149 * MethodHandle fini = (body.type().returnType() == void.class
6150 * ? null : identity(body.type().returnType()));
6151 * MethodHandle[]
6152 * checkExit = { null, null, pred, fini },
6153 * varBody = { init, body };
6154 * return loop(checkExit, varBody);
6155 * }
6156 * }</pre></blockquote>
6157 *
6158 * @param init optional initializer, providing the initial value of the loop variable.
6159 * May be {@code null}, implying a default initial value. See above for other constraints.
6160 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6161 * above for other constraints.
6162 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6163 * See above for other constraints.
6164 *
6165 * @return a method handle implementing the {@code while} loop as described by the arguments.
6166 * @throws IllegalArgumentException if the rules for the arguments are violated.
6167 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6168 *
6169 * @see #loop(MethodHandle[][])
6170 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6171 * @since 9
6172 */
6173 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6174 whileLoopChecks(init, pred, body);
6175 MethodHandle fini = identityOrVoid(body.type().returnType());
6176 MethodHandle[] checkExit = { null, null, pred, fini };
6177 MethodHandle[] varBody = { init, body };
6178 return loop(checkExit, varBody);
6179 }
6180
6181 /**
6182 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6183 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6184 * <p>
6185 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6186 * method will, in each iteration, first execute its body and then evaluate the predicate.
6187 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6188 * <p>
6189 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6190 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6191 * and updated with the value returned from its invocation. The result of loop execution will be
6192 * the final value of the additional loop-local variable (if present).
6193 * <p>
6194 * The following rules hold for these argument handles:<ul>
6195 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6196 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6197 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6198 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6199 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6200 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6201 * It will constrain the parameter lists of the other loop parts.
6202 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6203 * list {@code (A...)} is called the <em>external parameter list</em>.
6204 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6205 * additional state variable of the loop.
6206 * The body must both accept and return a value of this type {@code V}.
6207 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6208 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6209 * <a href="MethodHandles.html#effid">effectively identical</a>
6210 * to the external parameter list {@code (A...)}.
6211 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6212 * {@linkplain #empty default value}.
6213 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6214 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6215 * effectively identical to the internal parameter list.
6216 * </ul>
6217 * <p>
6218 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6219 * <li>The loop handle's result type is the result type {@code V} of the body.
6220 * <li>The loop handle's parameter types are the types {@code (A...)},
6221 * from the external parameter list.
6222 * </ul>
6223 * <p>
6224 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6225 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6226 * passed to the loop.
6227 * <blockquote><pre>{@code
6228 * V init(A...);
6229 * boolean pred(V, A...);
6230 * V body(V, A...);
6231 * V doWhileLoop(A... a...) {
6232 * V v = init(a...);
6233 * do {
6234 * v = body(v, a...);
6235 * } while (pred(v, a...));
6236 * return v;
6237 * }
6238 * }</pre></blockquote>
6239 *
6240 * @apiNote Example:
6241 * <blockquote><pre>{@code
6242 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6243 * static int zero(int limit) { return 0; }
6244 * static int step(int i, int limit) { return i + 1; }
6245 * static boolean pred(int i, int limit) { return i < limit; }
6246 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6247 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6248 * assertEquals(23, loop.invoke(23));
6249 * }</pre></blockquote>
6250 *
6251 *
6252 * @apiNote The implementation of this method can be expressed as follows:
6253 * <blockquote><pre>{@code
6254 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6255 * MethodHandle fini = (body.type().returnType() == void.class
6256 * ? null : identity(body.type().returnType()));
6257 * MethodHandle[] clause = { init, body, pred, fini };
6258 * return loop(clause);
6259 * }
6260 * }</pre></blockquote>
6261 *
6262 * @param init optional initializer, providing the initial value of the loop variable.
6263 * May be {@code null}, implying a default initial value. See above for other constraints.
6264 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6265 * See above for other constraints.
6266 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6267 * above for other constraints.
6268 *
6269 * @return a method handle implementing the {@code while} loop as described by the arguments.
6270 * @throws IllegalArgumentException if the rules for the arguments are violated.
6271 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6272 *
6273 * @see #loop(MethodHandle[][])
6274 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6275 * @since 9
6276 */
6277 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6278 whileLoopChecks(init, pred, body);
6279 MethodHandle fini = identityOrVoid(body.type().returnType());
6280 MethodHandle[] clause = {init, body, pred, fini };
6281 return loop(clause);
6282 }
6283
6284 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6285 Objects.requireNonNull(pred);
6286 Objects.requireNonNull(body);
6287 MethodType bodyType = body.type();
6288 Class<?> returnType = bodyType.returnType();
6289 List<Class<?>> innerList = bodyType.parameterList();
6290 List<Class<?>> outerList = innerList;
6291 if (returnType == void.class) {
6292 // OK
6293 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
6294 // leading V argument missing => error
6295 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6296 throw misMatchedTypes("body function", bodyType, expected);
6297 } else {
6298 outerList = innerList.subList(1, innerList.size());
6299 }
6300 MethodType predType = pred.type();
6301 if (predType.returnType() != boolean.class ||
6302 !predType.effectivelyIdenticalParameters(0, innerList)) {
6303 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6304 }
6305 if (init != null) {
6306 MethodType initType = init.type();
6307 if (initType.returnType() != returnType ||
6308 !initType.effectivelyIdenticalParameters(0, outerList)) {
6309 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6310 }
6311 }
6312 }
6313
6314 /**
6315 * Constructs a loop that runs a given number of iterations.
6316 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6317 * <p>
6318 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6319 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6320 * It will be initialized to 0 and incremented by 1 in each iteration.
6321 * <p>
6322 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6323 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6324 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6325 * <p>
6326 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6327 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6328 * iteration variable.
6329 * The result of the loop handle execution will be the final {@code V} value of that variable
6330 * (or {@code void} if there is no {@code V} variable).
6331 * <p>
6332 * The following rules hold for the argument handles:<ul>
6333 * <li>The {@code iterations} handle must not be {@code null}, and must return
6334 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6335 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6336 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6337 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6338 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6339 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6340 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6341 * of types called the <em>internal parameter list</em>.
6342 * It will constrain the parameter lists of the other loop parts.
6343 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6344 * with no additional {@code A} types, then the internal parameter list is extended by
6345 * the argument types {@code A...} of the {@code iterations} handle.
6346 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6347 * list {@code (A...)} is called the <em>external parameter list</em>.
6348 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6349 * additional state variable of the loop.
6350 * The body must both accept a leading parameter and return a value of this type {@code V}.
6351 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6352 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6353 * <a href="MethodHandles.html#effid">effectively identical</a>
6354 * to the external parameter list {@code (A...)}.
6355 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6356 * {@linkplain #empty default value}.
6357 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6358 * effectively identical to the external parameter list {@code (A...)}.
6359 * </ul>
6360 * <p>
6361 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6362 * <li>The loop handle's result type is the result type {@code V} of the body.
6363 * <li>The loop handle's parameter types are the types {@code (A...)},
6364 * from the external parameter list.
6365 * </ul>
6366 * <p>
6367 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6368 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6369 * arguments passed to the loop.
6370 * <blockquote><pre>{@code
6371 * int iterations(A...);
6372 * V init(A...);
6373 * V body(V, int, A...);
6374 * V countedLoop(A... a...) {
6375 * int end = iterations(a...);
6376 * V v = init(a...);
6377 * for (int i = 0; i < end; ++i) {
6378 * v = body(v, i, a...);
6379 * }
6380 * return v;
6381 * }
6382 * }</pre></blockquote>
6383 *
6384 * @apiNote Example with a fully conformant body method:
6385 * <blockquote><pre>{@code
6386 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6387 * // => a variation on a well known theme
6388 * static String step(String v, int counter, String init) { return "na " + v; }
6389 * // assume MH_step is a handle to the method above
6390 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6391 * MethodHandle start = MethodHandles.identity(String.class);
6392 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6393 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6394 * }</pre></blockquote>
6395 *
6396 * @apiNote Example with the simplest possible body method type,
6397 * and passing the number of iterations to the loop invocation:
6398 * <blockquote><pre>{@code
6399 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6400 * // => a variation on a well known theme
6401 * static String step(String v, int counter ) { return "na " + v; }
6402 * // assume MH_step is a handle to the method above
6403 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6404 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6405 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6406 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6407 * }</pre></blockquote>
6408 *
6409 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6410 * as loop parameters:
6411 * <blockquote><pre>{@code
6412 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6413 * // => a variation on a well known theme
6414 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6415 * // assume MH_step is a handle to the method above
6416 * MethodHandle count = MethodHandles.identity(int.class);
6417 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6418 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6419 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6420 * }</pre></blockquote>
6421 *
6422 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6423 * to enforce a loop type:
6424 * <blockquote><pre>{@code
6425 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6426 * // => a variation on a well known theme
6427 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6428 * // assume MH_step is a handle to the method above
6429 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6430 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6431 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6432 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6433 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6434 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6435 * }</pre></blockquote>
6436 *
6437 * @apiNote The implementation of this method can be expressed as follows:
6438 * <blockquote><pre>{@code
6439 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6440 * return countedLoop(empty(iterations.type()), iterations, init, body);
6441 * }
6442 * }</pre></blockquote>
6443 *
6444 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6445 * result type must be {@code int}. See above for other constraints.
6446 * @param init optional initializer, providing the initial value of the loop variable.
6447 * May be {@code null}, implying a default initial value. See above for other constraints.
6448 * @param body body of the loop, which may not be {@code null}.
6449 * It controls the loop parameters and result type in the standard case (see above for details).
6450 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6451 * and may accept any number of additional types.
6452 * See above for other constraints.
6453 *
6454 * @return a method handle representing the loop.
6455 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6456 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6457 *
6458 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6459 * @since 9
6460 */
6461 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6462 return countedLoop(empty(iterations.type()), iterations, init, body);
6463 }
6464
6465 /**
6466 * Constructs a loop that counts over a range of numbers.
6467 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6468 * <p>
6469 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
6470 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
6471 * values of the loop counter.
6472 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
6473 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
6474 * <p>
6475 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6476 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6477 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6478 * <p>
6479 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6480 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6481 * iteration variable.
6482 * The result of the loop handle execution will be the final {@code V} value of that variable
6483 * (or {@code void} if there is no {@code V} variable).
6484 * <p>
6485 * The following rules hold for the argument handles:<ul>
6486 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
6487 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
6488 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6489 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6490 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6491 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6492 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6493 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6494 * of types called the <em>internal parameter list</em>.
6495 * It will constrain the parameter lists of the other loop parts.
6496 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6497 * with no additional {@code A} types, then the internal parameter list is extended by
6498 * the argument types {@code A...} of the {@code end} handle.
6499 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6500 * list {@code (A...)} is called the <em>external parameter list</em>.
6501 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6502 * additional state variable of the loop.
6503 * The body must both accept a leading parameter and return a value of this type {@code V}.
6504 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6505 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6506 * <a href="MethodHandles.html#effid">effectively identical</a>
6507 * to the external parameter list {@code (A...)}.
6508 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6509 * {@linkplain #empty default value}.
6510 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
6511 * effectively identical to the external parameter list {@code (A...)}.
6512 * <li>Likewise, the parameter list of {@code end} must be effectively identical
6513 * to the external parameter list.
6514 * </ul>
6515 * <p>
6516 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6517 * <li>The loop handle's result type is the result type {@code V} of the body.
6518 * <li>The loop handle's parameter types are the types {@code (A...)},
6519 * from the external parameter list.
6520 * </ul>
6521 * <p>
6522 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6523 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6524 * arguments passed to the loop.
6525 * <blockquote><pre>{@code
6526 * int start(A...);
6527 * int end(A...);
6528 * V init(A...);
6529 * V body(V, int, A...);
6530 * V countedLoop(A... a...) {
6531 * int e = end(a...);
6532 * int s = start(a...);
6533 * V v = init(a...);
6534 * for (int i = s; i < e; ++i) {
6535 * v = body(v, i, a...);
6536 * }
6537 * return v;
6538 * }
6539 * }</pre></blockquote>
6540 *
6541 * @apiNote The implementation of this method can be expressed as follows:
6542 * <blockquote><pre>{@code
6543 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6544 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
6545 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
6546 * // the following semantics:
6547 * // MH_increment: (int limit, int counter) -> counter + 1
6548 * // MH_predicate: (int limit, int counter) -> counter < limit
6549 * Class<?> counterType = start.type().returnType(); // int
6550 * Class<?> returnType = body.type().returnType();
6551 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
6552 * if (returnType != void.class) { // ignore the V variable
6553 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6554 * pred = dropArguments(pred, 1, returnType); // ditto
6555 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
6556 * }
6557 * body = dropArguments(body, 0, counterType); // ignore the limit variable
6558 * MethodHandle[]
6559 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6560 * bodyClause = { init, body }, // v = init(); v = body(v, i)
6561 * indexVar = { start, incr }; // i = start(); i = i + 1
6562 * return loop(loopLimit, bodyClause, indexVar);
6563 * }
6564 * }</pre></blockquote>
6565 *
6566 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
6567 * See above for other constraints.
6568 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
6569 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
6570 * @param init optional initializer, providing the initial value of the loop variable.
6571 * May be {@code null}, implying a default initial value. See above for other constraints.
6572 * @param body body of the loop, which may not be {@code null}.
6573 * It controls the loop parameters and result type in the standard case (see above for details).
6574 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6575 * and may accept any number of additional types.
6576 * See above for other constraints.
6577 *
6578 * @return a method handle representing the loop.
6579 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
6580 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6581 *
6582 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
6583 * @since 9
6584 */
6585 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6586 countedLoopChecks(start, end, init, body);
6587 Class<?> counterType = start.type().returnType(); // int, but who's counting?
6588 Class<?> limitType = end.type().returnType(); // yes, int again
6589 Class<?> returnType = body.type().returnType();
6590 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
6591 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
6592 MethodHandle retv = null;
6593 if (returnType != void.class) {
6594 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6595 pred = dropArguments(pred, 1, returnType); // ditto
6596 retv = dropArguments(identity(returnType), 0, counterType);
6597 }
6598 body = dropArguments(body, 0, counterType); // ignore the limit variable
6599 MethodHandle[]
6600 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6601 bodyClause = { init, body }, // v = init(); v = body(v, i)
6602 indexVar = { start, incr }; // i = start(); i = i + 1
6603 return loop(loopLimit, bodyClause, indexVar);
6604 }
6605
6606 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6607 Objects.requireNonNull(start);
6608 Objects.requireNonNull(end);
6609 Objects.requireNonNull(body);
6610 Class<?> counterType = start.type().returnType();
6611 if (counterType != int.class) {
6612 MethodType expected = start.type().changeReturnType(int.class);
6613 throw misMatchedTypes("start function", start.type(), expected);
6614 } else if (end.type().returnType() != counterType) {
6615 MethodType expected = end.type().changeReturnType(counterType);
6616 throw misMatchedTypes("end function", end.type(), expected);
6617 }
6618 MethodType bodyType = body.type();
6619 Class<?> returnType = bodyType.returnType();
6620 List<Class<?>> innerList = bodyType.parameterList();
6621 // strip leading V value if present
6622 int vsize = (returnType == void.class ? 0 : 1);
6623 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
6624 // argument list has no "V" => error
6625 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6626 throw misMatchedTypes("body function", bodyType, expected);
6627 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
6628 // missing I type => error
6629 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
6630 throw misMatchedTypes("body function", bodyType, expected);
6631 }
6632 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
6633 if (outerList.isEmpty()) {
6634 // special case; take lists from end handle
6635 outerList = end.type().parameterList();
6636 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
6637 }
6638 MethodType expected = methodType(counterType, outerList);
6639 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
6640 throw misMatchedTypes("start parameter types", start.type(), expected);
6641 }
6642 if (end.type() != start.type() &&
6643 !end.type().effectivelyIdenticalParameters(0, outerList)) {
6644 throw misMatchedTypes("end parameter types", end.type(), expected);
6645 }
6646 if (init != null) {
6647 MethodType initType = init.type();
6648 if (initType.returnType() != returnType ||
6649 !initType.effectivelyIdenticalParameters(0, outerList)) {
6650 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6651 }
6652 }
6653 }
6654
6655 /**
6656 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
6657 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6658 * <p>
6659 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
6660 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
6661 * <p>
6662 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6663 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6664 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6665 * <p>
6666 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6667 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6668 * iteration variable.
6669 * The result of the loop handle execution will be the final {@code V} value of that variable
6670 * (or {@code void} if there is no {@code V} variable).
6671 * <p>
6672 * The following rules hold for the argument handles:<ul>
6673 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6674 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
6675 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6676 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
6677 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
6678 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
6679 * of types called the <em>internal parameter list</em>.
6680 * It will constrain the parameter lists of the other loop parts.
6681 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
6682 * with no additional {@code A} types, then the internal parameter list is extended by
6683 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
6684 * single type {@code Iterable} is added and constitutes the {@code A...} list.
6685 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
6686 * list {@code (A...)} is called the <em>external parameter list</em>.
6687 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6688 * additional state variable of the loop.
6689 * The body must both accept a leading parameter and return a value of this type {@code V}.
6690 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6691 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6692 * <a href="MethodHandles.html#effid">effectively identical</a>
6693 * to the external parameter list {@code (A...)}.
6694 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6695 * {@linkplain #empty default value}.
6696 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
6697 * type {@code java.util.Iterator} or a subtype thereof.
6698 * The iterator it produces when the loop is executed will be assumed
6699 * to yield values which can be converted to type {@code T}.
6700 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
6701 * effectively identical to the external parameter list {@code (A...)}.
6702 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
6703 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
6704 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
6705 * handle parameter is adjusted to accept the leading {@code A} type, as if by
6706 * the {@link MethodHandle#asType asType} conversion method.
6707 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
6708 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
6709 * </ul>
6710 * <p>
6711 * The type {@code T} may be either a primitive or reference.
6712 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
6713 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
6714 * as if by the {@link MethodHandle#asType asType} conversion method.
6715 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
6716 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
6717 * <p>
6718 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6719 * <li>The loop handle's result type is the result type {@code V} of the body.
6720 * <li>The loop handle's parameter types are the types {@code (A...)},
6721 * from the external parameter list.
6722 * </ul>
6723 * <p>
6724 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6725 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
6726 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
6727 * <blockquote><pre>{@code
6728 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
6729 * V init(A...);
6730 * V body(V,T,A...);
6731 * V iteratedLoop(A... a...) {
6732 * Iterator<T> it = iterator(a...);
6733 * V v = init(a...);
6734 * while (it.hasNext()) {
6735 * T t = it.next();
6736 * v = body(v, t, a...);
6737 * }
6738 * return v;
6739 * }
6740 * }</pre></blockquote>
6741 *
6742 * @apiNote Example:
6743 * <blockquote><pre>{@code
6744 * // get an iterator from a list
6745 * static List<String> reverseStep(List<String> r, String e) {
6746 * r.add(0, e);
6747 * return r;
6748 * }
6749 * static List<String> newArrayList() { return new ArrayList<>(); }
6750 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
6751 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
6752 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
6753 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
6754 * assertEquals(reversedList, (List<String>) loop.invoke(list));
6755 * }</pre></blockquote>
6756 *
6757 * @apiNote The implementation of this method can be expressed approximately as follows:
6758 * <blockquote><pre>{@code
6759 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6760 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
6761 * Class<?> returnType = body.type().returnType();
6762 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6763 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
6764 * MethodHandle retv = null, step = body, startIter = iterator;
6765 * if (returnType != void.class) {
6766 * // the simple thing first: in (I V A...), drop the I to get V
6767 * retv = dropArguments(identity(returnType), 0, Iterator.class);
6768 * // body type signature (V T A...), internal loop types (I V A...)
6769 * step = swapArguments(body, 0, 1); // swap V <-> T
6770 * }
6771 * if (startIter == null) startIter = MH_getIter;
6772 * MethodHandle[]
6773 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
6774 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
6775 * return loop(iterVar, bodyClause);
6776 * }
6777 * }</pre></blockquote>
6778 *
6779 * @param iterator an optional handle to return the iterator to start the loop.
6780 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
6781 * See above for other constraints.
6782 * @param init optional initializer, providing the initial value of the loop variable.
6783 * May be {@code null}, implying a default initial value. See above for other constraints.
6784 * @param body body of the loop, which may not be {@code null}.
6785 * It controls the loop parameters and result type in the standard case (see above for details).
6786 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
6787 * and may accept any number of additional types.
6788 * See above for other constraints.
6789 *
6790 * @return a method handle embodying the iteration loop functionality.
6791 * @throws NullPointerException if the {@code body} handle is {@code null}.
6792 * @throws IllegalArgumentException if any argument violates the above requirements.
6793 *
6794 * @since 9
6795 */
6796 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6797 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
6798 Class<?> returnType = body.type().returnType();
6799 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
6800 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
6801 MethodHandle startIter;
6802 MethodHandle nextVal;
6803 {
6804 MethodType iteratorType;
6805 if (iterator == null) {
6806 // derive argument type from body, if available, else use Iterable
6807 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
6808 iteratorType = startIter.type().changeParameterType(0, iterableType);
6809 } else {
6810 // force return type to the internal iterator class
6811 iteratorType = iterator.type().changeReturnType(Iterator.class);
6812 startIter = iterator;
6813 }
6814 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6815 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
6816
6817 // perform the asType transforms under an exception transformer, as per spec.:
6818 try {
6819 startIter = startIter.asType(iteratorType);
6820 nextVal = nextRaw.asType(nextValType);
6821 } catch (WrongMethodTypeException ex) {
6822 throw new IllegalArgumentException(ex);
6823 }
6824 }
6825
6826 MethodHandle retv = null, step = body;
6827 if (returnType != void.class) {
6828 // the simple thing first: in (I V A...), drop the I to get V
6829 retv = dropArguments(identity(returnType), 0, Iterator.class);
6830 // body type signature (V T A...), internal loop types (I V A...)
6831 step = swapArguments(body, 0, 1); // swap V <-> T
6832 }
6833
6834 MethodHandle[]
6835 iterVar = { startIter, null, hasNext, retv },
6836 bodyClause = { init, filterArgument(step, 0, nextVal) };
6837 return loop(iterVar, bodyClause);
6838 }
6839
6840 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6841 Objects.requireNonNull(body);
6842 MethodType bodyType = body.type();
6843 Class<?> returnType = bodyType.returnType();
6844 List<Class<?>> internalParamList = bodyType.parameterList();
6845 // strip leading V value if present
6846 int vsize = (returnType == void.class ? 0 : 1);
6847 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
6848 // argument list has no "V" => error
6849 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6850 throw misMatchedTypes("body function", bodyType, expected);
6851 } else if (internalParamList.size() <= vsize) {
6852 // missing T type => error
6853 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
6854 throw misMatchedTypes("body function", bodyType, expected);
6855 }
6856 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
6857 Class<?> iterableType = null;
6858 if (iterator != null) {
6859 // special case; if the body handle only declares V and T then
6860 // the external parameter list is obtained from iterator handle
6861 if (externalParamList.isEmpty()) {
6862 externalParamList = iterator.type().parameterList();
6863 }
6864 MethodType itype = iterator.type();
6865 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
6866 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
6867 }
6868 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
6869 MethodType expected = methodType(itype.returnType(), externalParamList);
6870 throw misMatchedTypes("iterator parameters", itype, expected);
6871 }
6872 } else {
6873 if (externalParamList.isEmpty()) {
6874 // special case; if the iterator handle is null and the body handle
6875 // only declares V and T then the external parameter list consists
6876 // of Iterable
6877 externalParamList = Arrays.asList(Iterable.class);
6878 iterableType = Iterable.class;
6879 } else {
6880 // special case; if the iterator handle is null and the external
6881 // parameter list is not empty then the first parameter must be
6882 // assignable to Iterable
6883 iterableType = externalParamList.get(0);
6884 if (!Iterable.class.isAssignableFrom(iterableType)) {
6885 throw newIllegalArgumentException(
6886 "inferred first loop argument must inherit from Iterable: " + iterableType);
6887 }
6888 }
6889 }
6890 if (init != null) {
6891 MethodType initType = init.type();
6892 if (initType.returnType() != returnType ||
6893 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
6894 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
6895 }
6896 }
6897 return iterableType; // help the caller a bit
6898 }
6899
6900 /*non-public*/
6901 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
6902 // there should be a better way to uncross my wires
6903 int arity = mh.type().parameterCount();
6904 int[] order = new int[arity];
6905 for (int k = 0; k < arity; k++) order[k] = k;
6906 order[i] = j; order[j] = i;
6907 Class<?>[] types = mh.type().parameterArray();
6908 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
6909 MethodType swapType = methodType(mh.type().returnType(), types);
6910 return permuteArguments(mh, swapType, order);
6911 }
6912
6913 /**
6914 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
6915 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
6916 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
6917 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
6918 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
6919 * {@code try-finally} handle.
6920 * <p>
6921 * The {@code cleanup} handle will be passed one or two additional leading arguments.
6922 * The first is the exception thrown during the
6923 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
6924 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
6925 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
6926 * The second argument is not present if the {@code target} handle has a {@code void} return type.
6927 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
6928 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
6929 * <p>
6930 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
6931 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
6932 * two extra leading parameters:<ul>
6933 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
6934 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
6935 * the result from the execution of the {@code target} handle.
6936 * This parameter is not present if the {@code target} returns {@code void}.
6937 * </ul>
6938 * <p>
6939 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
6940 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
6941 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
6942 * the cleanup.
6943 * <blockquote><pre>{@code
6944 * V target(A..., B...);
6945 * V cleanup(Throwable, V, A...);
6946 * V adapter(A... a, B... b) {
6947 * V result = (zero value for V);
6948 * Throwable throwable = null;
6949 * try {
6950 * result = target(a..., b...);
6951 * } catch (Throwable t) {
6952 * throwable = t;
6953 * throw t;
6954 * } finally {
6955 * result = cleanup(throwable, result, a...);
6956 * }
6957 * return result;
6958 * }
6959 * }</pre></blockquote>
6960 * <p>
6961 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6962 * be modified by execution of the target, and so are passed unchanged
6963 * from the caller to the cleanup, if it is invoked.
6964 * <p>
6965 * The target and cleanup must return the same type, even if the cleanup
6966 * always throws.
6967 * To create such a throwing cleanup, compose the cleanup logic
6968 * with {@link #throwException throwException},
6969 * in order to create a method handle of the correct return type.
6970 * <p>
6971 * Note that {@code tryFinally} never converts exceptions into normal returns.
6972 * In rare cases where exceptions must be converted in that way, first wrap
6973 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
6974 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
6975 * <p>
6976 * It is recommended that the first parameter type of {@code cleanup} be
6977 * declared {@code Throwable} rather than a narrower subtype. This ensures
6978 * {@code cleanup} will always be invoked with whatever exception that
6979 * {@code target} throws. Declaring a narrower type may result in a
6980 * {@code ClassCastException} being thrown by the {@code try-finally}
6981 * handle if the type of the exception thrown by {@code target} is not
6982 * assignable to the first parameter type of {@code cleanup}. Note that
6983 * various exception types of {@code VirtualMachineError},
6984 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6985 * thrown by almost any kind of Java code, and a finally clause that
6986 * catches (say) only {@code IOException} would mask any of the others
6987 * behind a {@code ClassCastException}.
6988 *
6989 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6990 * @param cleanup the handle that is invoked in the finally block.
6991 *
6992 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6993 * @throws NullPointerException if any argument is null
6994 * @throws IllegalArgumentException if {@code cleanup} does not accept
6995 * the required leading arguments, or if the method handle types do
6996 * not match in their return types and their
6997 * corresponding trailing parameters
6998 *
6999 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7000 * @since 9
7001 */
7002 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7003 List<Class<?>> targetParamTypes = target.type().parameterList();
7004 Class<?> rtype = target.type().returnType();
7005
7006 tryFinallyChecks(target, cleanup);
7007
7008 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7009 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7010 // target parameter list.
7011 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
7012
7013 // Ensure that the intrinsic type checks the instance thrown by the
7014 // target against the first parameter of cleanup
7015 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7016
7017 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7018 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7019 }
7020
7021 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7022 Class<?> rtype = target.type().returnType();
7023 if (rtype != cleanup.type().returnType()) {
7024 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7025 }
7026 MethodType cleanupType = cleanup.type();
7027 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7028 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7029 }
7030 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7031 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7032 }
7033 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7034 // target parameter list.
7035 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7036 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7037 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7038 cleanup.type(), target.type());
7039 }
7040 }
7041
7042 }