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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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25
26 package java.lang.invoke;
27
28
29 import java.util.*;
30 import jdk.internal.HotSpotIntrinsicCandidate;
31
32 import static java.lang.invoke.MethodHandleStatics.*;
33
34 /**
35 * A method handle is a typed, directly executable reference to an underlying method,
36 * constructor, field, or similar low-level operation, with optional
37 * transformations of arguments or return values.
38 * These transformations are quite general, and include such patterns as
39 * {@linkplain #asType conversion},
40 * {@linkplain #bindTo insertion},
41 * {@linkplain java.lang.invoke.MethodHandles#dropArguments deletion},
42 * and {@linkplain java.lang.invoke.MethodHandles#filterArguments substitution}.
43 *
44 * <h1>Method handle contents</h1>
45 * Method handles are dynamically and strongly typed according to their parameter and return types.
46 * They are not distinguished by the name or the defining class of their underlying methods.
47 * A method handle must be invoked using a symbolic type descriptor which matches
48 * the method handle's own {@linkplain #type type descriptor}.
49 * <p>
50 * Every method handle reports its type descriptor via the {@link #type type} accessor.
51 * This type descriptor is a {@link java.lang.invoke.MethodType MethodType} object,
52 * whose structure is a series of classes, one of which is
53 * the return type of the method (or {@code void.class} if none).
54 * <p>
55 * A method handle's type controls the types of invocations it accepts,
56 * and the kinds of transformations that apply to it.
57 * <p>
58 * A method handle contains a pair of special invoker methods
59 * called {@link #invokeExact invokeExact} and {@link #invoke invoke}.
60 * Both invoker methods provide direct access to the method handle's
61 * underlying method, constructor, field, or other operation,
62 * as modified by transformations of arguments and return values.
63 * Both invokers accept calls which exactly match the method handle's own type.
64 * The plain, inexact invoker also accepts a range of other call types.
65 * <p>
66 * Method handles are immutable and have no visible state.
67 * Of course, they can be bound to underlying methods or data which exhibit state.
68 * With respect to the Java Memory Model, any method handle will behave
69 * as if all of its (internal) fields are final variables. This means that any method
70 * handle made visible to the application will always be fully formed.
71 * This is true even if the method handle is published through a shared
72 * variable in a data race.
73 * <p>
74 * Method handles cannot be subclassed by the user.
75 * Implementations may (or may not) create internal subclasses of {@code MethodHandle}
76 * which may be visible via the {@link java.lang.Object#getClass Object.getClass}
77 * operation. The programmer should not draw conclusions about a method handle
78 * from its specific class, as the method handle class hierarchy (if any)
79 * may change from time to time or across implementations from different vendors.
80 *
81 * <h1>Method handle compilation</h1>
82 * A Java method call expression naming {@code invokeExact} or {@code invoke}
83 * can invoke a method handle from Java source code.
84 * From the viewpoint of source code, these methods can take any arguments
85 * and their result can be cast to any return type.
86 * Formally this is accomplished by giving the invoker methods
87 * {@code Object} return types and variable arity {@code Object} arguments,
88 * but they have an additional quality called <em>signature polymorphism</em>
89 * which connects this freedom of invocation directly to the JVM execution stack.
90 * <p>
91 * As is usual with virtual methods, source-level calls to {@code invokeExact}
92 * and {@code invoke} compile to an {@code invokevirtual} instruction.
93 * More unusually, the compiler must record the actual argument types,
94 * and may not perform method invocation conversions on the arguments.
95 * Instead, it must push them on the stack according to their own unconverted types.
96 * The method handle object itself is pushed on the stack before the arguments.
97 * The compiler then calls the method handle with a symbolic type descriptor which
98 * describes the argument and return types.
99 * <p>
100 * To issue a complete symbolic type descriptor, the compiler must also determine
101 * the return type. This is based on a cast on the method invocation expression,
102 * if there is one, or else {@code Object} if the invocation is an expression
103 * or else {@code void} if the invocation is a statement.
104 * The cast may be to a primitive type (but not {@code void}).
105 * <p>
106 * As a corner case, an uncasted {@code null} argument is given
107 * a symbolic type descriptor of {@code java.lang.Void}.
108 * The ambiguity with the type {@code Void} is harmless, since there are no references of type
109 * {@code Void} except the null reference.
110 *
111 * <h1>Method handle invocation</h1>
112 * The first time a {@code invokevirtual} instruction is executed
113 * it is linked, by symbolically resolving the names in the instruction
114 * and verifying that the method call is statically legal.
115 * This is true of calls to {@code invokeExact} and {@code invoke}.
116 * In this case, the symbolic type descriptor emitted by the compiler is checked for
117 * correct syntax and names it contains are resolved.
118 * Thus, an {@code invokevirtual} instruction which invokes
119 * a method handle will always link, as long
120 * as the symbolic type descriptor is syntactically well-formed
121 * and the types exist.
122 * <p>
123 * When the {@code invokevirtual} is executed after linking,
124 * the receiving method handle's type is first checked by the JVM
125 * to ensure that it matches the symbolic type descriptor.
126 * If the type match fails, it means that the method which the
127 * caller is invoking is not present on the individual
128 * method handle being invoked.
129 * <p>
130 * In the case of {@code invokeExact}, the type descriptor of the invocation
131 * (after resolving symbolic type names) must exactly match the method type
132 * of the receiving method handle.
133 * In the case of plain, inexact {@code invoke}, the resolved type descriptor
134 * must be a valid argument to the receiver's {@link #asType asType} method.
135 * Thus, plain {@code invoke} is more permissive than {@code invokeExact}.
136 * <p>
137 * After type matching, a call to {@code invokeExact} directly
138 * and immediately invoke the method handle's underlying method
139 * (or other behavior, as the case may be).
140 * <p>
141 * A call to plain {@code invoke} works the same as a call to
142 * {@code invokeExact}, if the symbolic type descriptor specified by the caller
143 * exactly matches the method handle's own type.
144 * If there is a type mismatch, {@code invoke} attempts
145 * to adjust the type of the receiving method handle,
146 * as if by a call to {@link #asType asType},
147 * to obtain an exactly invokable method handle {@code M2}.
148 * This allows a more powerful negotiation of method type
149 * between caller and callee.
150 * <p>
151 * (<em>Note:</em> The adjusted method handle {@code M2} is not directly observable,
152 * and implementations are therefore not required to materialize it.)
153 *
154 * <h1>Invocation checking</h1>
155 * In typical programs, method handle type matching will usually succeed.
156 * But if a match fails, the JVM will throw a {@link WrongMethodTypeException},
157 * either directly (in the case of {@code invokeExact}) or indirectly as if
158 * by a failed call to {@code asType} (in the case of {@code invoke}).
159 * <p>
160 * Thus, a method type mismatch which might show up as a linkage error
161 * in a statically typed program can show up as
162 * a dynamic {@code WrongMethodTypeException}
163 * in a program which uses method handles.
164 * <p>
165 * Because method types contain "live" {@code Class} objects,
166 * method type matching takes into account both types names and class loaders.
167 * Thus, even if a method handle {@code M} is created in one
168 * class loader {@code L1} and used in another {@code L2},
169 * method handle calls are type-safe, because the caller's symbolic type
170 * descriptor, as resolved in {@code L2},
171 * is matched against the original callee method's symbolic type descriptor,
172 * as resolved in {@code L1}.
173 * The resolution in {@code L1} happens when {@code M} is created
174 * and its type is assigned, while the resolution in {@code L2} happens
175 * when the {@code invokevirtual} instruction is linked.
176 * <p>
177 * Apart from the checking of type descriptors,
178 * a method handle's capability to call its underlying method is unrestricted.
179 * If a method handle is formed on a non-public method by a class
180 * that has access to that method, the resulting handle can be used
181 * in any place by any caller who receives a reference to it.
182 * <p>
183 * Unlike with the Core Reflection API, where access is checked every time
184 * a reflective method is invoked,
185 * method handle access checking is performed
186 * <a href="MethodHandles.Lookup.html#access">when the method handle is created</a>.
187 * In the case of {@code ldc} (see below), access checking is performed as part of linking
188 * the constant pool entry underlying the constant method handle.
189 * <p>
190 * Thus, handles to non-public methods, or to methods in non-public classes,
191 * should generally be kept secret.
192 * They should not be passed to untrusted code unless their use from
193 * the untrusted code would be harmless.
194 *
195 * <h1>Method handle creation</h1>
196 * Java code can create a method handle that directly accesses
197 * any method, constructor, or field that is accessible to that code.
198 * This is done via a reflective, capability-based API called
199 * {@link java.lang.invoke.MethodHandles.Lookup MethodHandles.Lookup}
200 * For example, a static method handle can be obtained
201 * from {@link java.lang.invoke.MethodHandles.Lookup#findStatic Lookup.findStatic}.
202 * There are also conversion methods from Core Reflection API objects,
203 * such as {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}.
204 * <p>
205 * Like classes and strings, method handles that correspond to accessible
206 * fields, methods, and constructors can also be represented directly
207 * in a class file's constant pool as constants to be loaded by {@code ldc} bytecodes.
208 * A new type of constant pool entry, {@code CONSTANT_MethodHandle},
209 * refers directly to an associated {@code CONSTANT_Methodref},
210 * {@code CONSTANT_InterfaceMethodref}, or {@code CONSTANT_Fieldref}
211 * constant pool entry.
212 * (For full details on method handle constants,
213 * see sections 4.4.8 and 5.4.3.5 of the Java Virtual Machine Specification.)
214 * <p>
215 * Method handles produced by lookups or constant loads from methods or
216 * constructors with the variable arity modifier bit ({@code 0x0080})
217 * have a corresponding variable arity, as if they were defined with
218 * the help of {@link #asVarargsCollector asVarargsCollector}
219 * or {@link #withVarargs withVarargs}.
220 * <p>
221 * A method reference may refer either to a static or non-static method.
222 * In the non-static case, the method handle type includes an explicit
223 * receiver argument, prepended before any other arguments.
224 * In the method handle's type, the initial receiver argument is typed
225 * according to the class under which the method was initially requested.
226 * (E.g., if a non-static method handle is obtained via {@code ldc},
227 * the type of the receiver is the class named in the constant pool entry.)
228 * <p>
229 * Method handle constants are subject to the same link-time access checks
230 * their corresponding bytecode instructions, and the {@code ldc} instruction
231 * will throw corresponding linkage errors if the bytecode behaviors would
232 * throw such errors.
233 * <p>
234 * As a corollary of this, access to protected members is restricted
235 * to receivers only of the accessing class, or one of its subclasses,
236 * and the accessing class must in turn be a subclass (or package sibling)
237 * of the protected member's defining class.
238 * If a method reference refers to a protected non-static method or field
239 * of a class outside the current package, the receiver argument will
240 * be narrowed to the type of the accessing class.
241 * <p>
242 * When a method handle to a virtual method is invoked, the method is
243 * always looked up in the receiver (that is, the first argument).
244 * <p>
245 * A non-virtual method handle to a specific virtual method implementation
246 * can also be created. These do not perform virtual lookup based on
247 * receiver type. Such a method handle simulates the effect of
248 * an {@code invokespecial} instruction to the same method.
249 *
250 * <h1>Usage examples</h1>
251 * Here are some examples of usage:
252 * <blockquote><pre>{@code
253 Object x, y; String s; int i;
254 MethodType mt; MethodHandle mh;
255 MethodHandles.Lookup lookup = MethodHandles.lookup();
256 // mt is (char,char)String
257 mt = MethodType.methodType(String.class, char.class, char.class);
258 mh = lookup.findVirtual(String.class, "replace", mt);
259 s = (String) mh.invokeExact("daddy",'d','n');
260 // invokeExact(Ljava/lang/String;CC)Ljava/lang/String;
261 assertEquals(s, "nanny");
262 // weakly typed invocation (using MHs.invoke)
263 s = (String) mh.invokeWithArguments("sappy", 'p', 'v');
264 assertEquals(s, "savvy");
265 // mt is (Object[])List
266 mt = MethodType.methodType(java.util.List.class, Object[].class);
267 mh = lookup.findStatic(java.util.Arrays.class, "asList", mt);
268 assert(mh.isVarargsCollector());
269 x = mh.invoke("one", "two");
270 // invoke(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/Object;
271 assertEquals(x, java.util.Arrays.asList("one","two"));
272 // mt is (Object,Object,Object)Object
273 mt = MethodType.genericMethodType(3);
274 mh = mh.asType(mt);
275 x = mh.invokeExact((Object)1, (Object)2, (Object)3);
276 // invokeExact(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
277 assertEquals(x, java.util.Arrays.asList(1,2,3));
278 // mt is ()int
279 mt = MethodType.methodType(int.class);
280 mh = lookup.findVirtual(java.util.List.class, "size", mt);
281 i = (int) mh.invokeExact(java.util.Arrays.asList(1,2,3));
282 // invokeExact(Ljava/util/List;)I
283 assert(i == 3);
284 mt = MethodType.methodType(void.class, String.class);
285 mh = lookup.findVirtual(java.io.PrintStream.class, "println", mt);
286 mh.invokeExact(System.out, "Hello, world.");
287 // invokeExact(Ljava/io/PrintStream;Ljava/lang/String;)V
288 * }</pre></blockquote>
289 * Each of the above calls to {@code invokeExact} or plain {@code invoke}
290 * generates a single invokevirtual instruction with
291 * the symbolic type descriptor indicated in the following comment.
292 * In these examples, the helper method {@code assertEquals} is assumed to
293 * be a method which calls {@link java.util.Objects#equals(Object,Object) Objects.equals}
294 * on its arguments, and asserts that the result is true.
295 *
296 * <h1>Exceptions</h1>
297 * The methods {@code invokeExact} and {@code invoke} are declared
298 * to throw {@link java.lang.Throwable Throwable},
299 * which is to say that there is no static restriction on what a method handle
300 * can throw. Since the JVM does not distinguish between checked
301 * and unchecked exceptions (other than by their class, of course),
302 * there is no particular effect on bytecode shape from ascribing
303 * checked exceptions to method handle invocations. But in Java source
304 * code, methods which perform method handle calls must either explicitly
305 * throw {@code Throwable}, or else must catch all
306 * throwables locally, rethrowing only those which are legal in the context,
307 * and wrapping ones which are illegal.
308 *
309 * <h1><a name="sigpoly"></a>Signature polymorphism</h1>
310 * The unusual compilation and linkage behavior of
311 * {@code invokeExact} and plain {@code invoke}
312 * is referenced by the term <em>signature polymorphism</em>.
313 * As defined in the Java Language Specification,
314 * a signature polymorphic method is one which can operate with
315 * any of a wide range of call signatures and return types.
316 * <p>
317 * In source code, a call to a signature polymorphic method will
318 * compile, regardless of the requested symbolic type descriptor.
319 * As usual, the Java compiler emits an {@code invokevirtual}
320 * instruction with the given symbolic type descriptor against the named method.
321 * The unusual part is that the symbolic type descriptor is derived from
322 * the actual argument and return types, not from the method declaration.
323 * <p>
324 * When the JVM processes bytecode containing signature polymorphic calls,
325 * it will successfully link any such call, regardless of its symbolic type descriptor.
326 * (In order to retain type safety, the JVM will guard such calls with suitable
327 * dynamic type checks, as described elsewhere.)
328 * <p>
329 * Bytecode generators, including the compiler back end, are required to emit
330 * untransformed symbolic type descriptors for these methods.
331 * Tools which determine symbolic linkage are required to accept such
332 * untransformed descriptors, without reporting linkage errors.
333 *
334 * <h1>Interoperation between method handles and the Core Reflection API</h1>
335 * Using factory methods in the {@link java.lang.invoke.MethodHandles.Lookup Lookup} API,
336 * any class member represented by a Core Reflection API object
337 * can be converted to a behaviorally equivalent method handle.
338 * For example, a reflective {@link java.lang.reflect.Method Method} can
339 * be converted to a method handle using
340 * {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}.
341 * The resulting method handles generally provide more direct and efficient
342 * access to the underlying class members.
343 * <p>
344 * As a special case,
345 * when the Core Reflection API is used to view the signature polymorphic
346 * methods {@code invokeExact} or plain {@code invoke} in this class,
347 * they appear as ordinary non-polymorphic methods.
348 * Their reflective appearance, as viewed by
349 * {@link java.lang.Class#getDeclaredMethod Class.getDeclaredMethod},
350 * is unaffected by their special status in this API.
351 * For example, {@link java.lang.reflect.Method#getModifiers Method.getModifiers}
352 * will report exactly those modifier bits required for any similarly
353 * declared method, including in this case {@code native} and {@code varargs} bits.
354 * <p>
355 * As with any reflected method, these methods (when reflected) may be
356 * invoked via {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}.
357 * However, such reflective calls do not result in method handle invocations.
358 * Such a call, if passed the required argument
359 * (a single one, of type {@code Object[]}), will ignore the argument and
360 * will throw an {@code UnsupportedOperationException}.
361 * <p>
362 * Since {@code invokevirtual} instructions can natively
363 * invoke method handles under any symbolic type descriptor, this reflective view conflicts
364 * with the normal presentation of these methods via bytecodes.
365 * Thus, these two native methods, when reflectively viewed by
366 * {@code Class.getDeclaredMethod}, may be regarded as placeholders only.
367 * <p>
368 * In order to obtain an invoker method for a particular type descriptor,
369 * use {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker},
370 * or {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}.
371 * The {@link java.lang.invoke.MethodHandles.Lookup#findVirtual Lookup.findVirtual}
372 * API is also able to return a method handle
373 * to call {@code invokeExact} or plain {@code invoke},
374 * for any specified type descriptor .
375 *
376 * <h1>Interoperation between method handles and Java generics</h1>
377 * A method handle can be obtained on a method, constructor, or field
378 * which is declared with Java generic types.
379 * As with the Core Reflection API, the type of the method handle
380 * will constructed from the erasure of the source-level type.
381 * When a method handle is invoked, the types of its arguments
382 * or the return value cast type may be generic types or type instances.
383 * If this occurs, the compiler will replace those
384 * types by their erasures when it constructs the symbolic type descriptor
385 * for the {@code invokevirtual} instruction.
386 * <p>
387 * Method handles do not represent
388 * their function-like types in terms of Java parameterized (generic) types,
389 * because there are three mismatches between function-like types and parameterized
390 * Java types.
391 * <ul>
392 * <li>Method types range over all possible arities,
393 * from no arguments to up to the <a href="MethodHandle.html#maxarity">maximum number</a> of allowed arguments.
394 * Generics are not variadic, and so cannot represent this.</li>
395 * <li>Method types can specify arguments of primitive types,
396 * which Java generic types cannot range over.</li>
397 * <li>Higher order functions over method handles (combinators) are
398 * often generic across a wide range of function types, including
399 * those of multiple arities. It is impossible to represent such
400 * genericity with a Java type parameter.</li>
401 * </ul>
402 *
403 * <h1><a name="maxarity"></a>Arity limits</h1>
404 * The JVM imposes on all methods and constructors of any kind an absolute
405 * limit of 255 stacked arguments. This limit can appear more restrictive
406 * in certain cases:
407 * <ul>
408 * <li>A {@code long} or {@code double} argument counts (for purposes of arity limits) as two argument slots.
409 * <li>A non-static method consumes an extra argument for the object on which the method is called.
410 * <li>A constructor consumes an extra argument for the object which is being constructed.
411 * <li>Since a method handle’s {@code invoke} method (or other signature-polymorphic method) is non-virtual,
412 * it consumes an extra argument for the method handle itself, in addition to any non-virtual receiver object.
413 * </ul>
414 * These limits imply that certain method handles cannot be created, solely because of the JVM limit on stacked arguments.
415 * For example, if a static JVM method accepts exactly 255 arguments, a method handle cannot be created for it.
416 * Attempts to create method handles with impossible method types lead to an {@link IllegalArgumentException}.
417 * In particular, a method handle’s type must not have an arity of the exact maximum 255.
418 *
419 * @see MethodType
420 * @see MethodHandles
421 * @author John Rose, JSR 292 EG
422 */
423 public abstract class MethodHandle {
424
425 /**
426 * Internal marker interface which distinguishes (to the Java compiler)
427 * those methods which are <a href="MethodHandle.html#sigpoly">signature polymorphic</a>.
428 */
429 @java.lang.annotation.Target({java.lang.annotation.ElementType.METHOD})
430 @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.RUNTIME)
431 @interface PolymorphicSignature { }
432
433 private final MethodType type;
434 /*private*/ final LambdaForm form;
435 // form is not private so that invokers can easily fetch it
436 /*private*/ MethodHandle asTypeCache;
437 // asTypeCache is not private so that invokers can easily fetch it
438 /*non-public*/ byte customizationCount;
439 // customizationCount should be accessible from invokers
440
441 /**
442 * Reports the type of this method handle.
443 * Every invocation of this method handle via {@code invokeExact} must exactly match this type.
444 * @return the method handle type
445 */
446 public MethodType type() {
447 return type;
448 }
449
450 /**
451 * Package-private constructor for the method handle implementation hierarchy.
452 * Method handle inheritance will be contained completely within
453 * the {@code java.lang.invoke} package.
454 */
455 // @param type type (permanently assigned) of the new method handle
456 /*non-public*/ MethodHandle(MethodType type, LambdaForm form) {
457 this.type = Objects.requireNonNull(type);
458 this.form = Objects.requireNonNull(form).uncustomize();
459
460 this.form.prepare(); // TO DO: Try to delay this step until just before invocation.
461 }
462
463 /**
464 * Invokes the method handle, allowing any caller type descriptor, but requiring an exact type match.
465 * The symbolic type descriptor at the call site of {@code invokeExact} must
466 * exactly match this method handle's {@link #type type}.
467 * No conversions are allowed on arguments or return values.
468 * <p>
469 * When this method is observed via the Core Reflection API,
470 * it will appear as a single native method, taking an object array and returning an object.
471 * If this native method is invoked directly via
472 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI,
473 * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect},
474 * it will throw an {@code UnsupportedOperationException}.
475 * @param args the signature-polymorphic parameter list, statically represented using varargs
476 * @return the signature-polymorphic result, statically represented using {@code Object}
477 * @throws WrongMethodTypeException if the target's type is not identical with the caller's symbolic type descriptor
478 * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call
479 */
480 @HotSpotIntrinsicCandidate
481 public final native @PolymorphicSignature Object invokeExact(Object... args) throws Throwable;
482
483 /**
484 * Invokes the method handle, allowing any caller type descriptor,
485 * and optionally performing conversions on arguments and return values.
486 * <p>
487 * If the call site's symbolic type descriptor exactly matches this method handle's {@link #type type},
488 * the call proceeds as if by {@link #invokeExact invokeExact}.
489 * <p>
490 * Otherwise, the call proceeds as if this method handle were first
491 * adjusted by calling {@link #asType asType} to adjust this method handle
492 * to the required type, and then the call proceeds as if by
493 * {@link #invokeExact invokeExact} on the adjusted method handle.
494 * <p>
495 * There is no guarantee that the {@code asType} call is actually made.
496 * If the JVM can predict the results of making the call, it may perform
497 * adaptations directly on the caller's arguments,
498 * and call the target method handle according to its own exact type.
499 * <p>
500 * The resolved type descriptor at the call site of {@code invoke} must
501 * be a valid argument to the receivers {@code asType} method.
502 * In particular, the caller must specify the same argument arity
503 * as the callee's type,
504 * if the callee is not a {@linkplain #asVarargsCollector variable arity collector}.
505 * <p>
506 * When this method is observed via the Core Reflection API,
507 * it will appear as a single native method, taking an object array and returning an object.
508 * If this native method is invoked directly via
509 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI,
510 * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect},
511 * it will throw an {@code UnsupportedOperationException}.
512 * @param args the signature-polymorphic parameter list, statically represented using varargs
513 * @return the signature-polymorphic result, statically represented using {@code Object}
514 * @throws WrongMethodTypeException if the target's type cannot be adjusted to the caller's symbolic type descriptor
515 * @throws ClassCastException if the target's type can be adjusted to the caller, but a reference cast fails
516 * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call
517 */
518 @HotSpotIntrinsicCandidate
519 public final native @PolymorphicSignature Object invoke(Object... args) throws Throwable;
520
521 /**
522 * Private method for trusted invocation of a method handle respecting simplified signatures.
523 * Type mismatches will not throw {@code WrongMethodTypeException}, but could crash the JVM.
524 * <p>
525 * The caller signature is restricted to the following basic types:
526 * Object, int, long, float, double, and void return.
527 * <p>
528 * The caller is responsible for maintaining type correctness by ensuring
529 * that the each outgoing argument value is a member of the range of the corresponding
530 * callee argument type.
531 * (The caller should therefore issue appropriate casts and integer narrowing
532 * operations on outgoing argument values.)
533 * The caller can assume that the incoming result value is part of the range
534 * of the callee's return type.
535 * @param args the signature-polymorphic parameter list, statically represented using varargs
536 * @return the signature-polymorphic result, statically represented using {@code Object}
537 */
538 @HotSpotIntrinsicCandidate
539 /*non-public*/ final native @PolymorphicSignature Object invokeBasic(Object... args) throws Throwable;
540
541 /**
542 * Private method for trusted invocation of a MemberName of kind {@code REF_invokeVirtual}.
543 * The caller signature is restricted to basic types as with {@code invokeBasic}.
544 * The trailing (not leading) argument must be a MemberName.
545 * @param args the signature-polymorphic parameter list, statically represented using varargs
546 * @return the signature-polymorphic result, statically represented using {@code Object}
547 */
548 @HotSpotIntrinsicCandidate
549 /*non-public*/ static native @PolymorphicSignature Object linkToVirtual(Object... args) throws Throwable;
550
551 /**
552 * Private method for trusted invocation of a MemberName of kind {@code REF_invokeStatic}.
553 * The caller signature is restricted to basic types as with {@code invokeBasic}.
554 * The trailing (not leading) argument must be a MemberName.
555 * @param args the signature-polymorphic parameter list, statically represented using varargs
556 * @return the signature-polymorphic result, statically represented using {@code Object}
557 */
558 @HotSpotIntrinsicCandidate
559 /*non-public*/ static native @PolymorphicSignature Object linkToStatic(Object... args) throws Throwable;
560
561 /**
562 * Private method for trusted invocation of a MemberName of kind {@code REF_invokeSpecial}.
563 * The caller signature is restricted to basic types as with {@code invokeBasic}.
564 * The trailing (not leading) argument must be a MemberName.
565 * @param args the signature-polymorphic parameter list, statically represented using varargs
566 * @return the signature-polymorphic result, statically represented using {@code Object}
567 */
568 @HotSpotIntrinsicCandidate
569 /*non-public*/ static native @PolymorphicSignature Object linkToSpecial(Object... args) throws Throwable;
570
571 /**
572 * Private method for trusted invocation of a MemberName of kind {@code REF_invokeInterface}.
573 * The caller signature is restricted to basic types as with {@code invokeBasic}.
574 * The trailing (not leading) argument must be a MemberName.
575 * @param args the signature-polymorphic parameter list, statically represented using varargs
576 * @return the signature-polymorphic result, statically represented using {@code Object}
577 */
578 @HotSpotIntrinsicCandidate
579 /*non-public*/ static native @PolymorphicSignature Object linkToInterface(Object... args) throws Throwable;
580
581 /**
582 * Performs a variable arity invocation, passing the arguments in the given list
583 * to the method handle, as if via an inexact {@link #invoke invoke} from a call site
584 * which mentions only the type {@code Object}, and whose arity is the length
585 * of the argument list.
586 * <p>
587 * Specifically, execution proceeds as if by the following steps,
588 * although the methods are not guaranteed to be called if the JVM
589 * can predict their effects.
590 * <ul>
591 * <li>Determine the length of the argument array as {@code N}.
592 * For a null reference, {@code N=0}. </li>
593 * <li>Determine the general type {@code TN} of {@code N} arguments as
594 * as {@code TN=MethodType.genericMethodType(N)}.</li>
595 * <li>Force the original target method handle {@code MH0} to the
596 * required type, as {@code MH1 = MH0.asType(TN)}. </li>
597 * <li>Spread the array into {@code N} separate arguments {@code A0, ...}. </li>
598 * <li>Invoke the type-adjusted method handle on the unpacked arguments:
599 * MH1.invokeExact(A0, ...). </li>
600 * <li>Take the return value as an {@code Object} reference. </li>
601 * </ul>
602 * <p>
603 * Because of the action of the {@code asType} step, the following argument
604 * conversions are applied as necessary:
605 * <ul>
606 * <li>reference casting
607 * <li>unboxing
608 * <li>widening primitive conversions
609 * </ul>
610 * <p>
611 * The result returned by the call is boxed if it is a primitive,
612 * or forced to null if the return type is void.
613 * <p>
614 * This call is equivalent to the following code:
615 * <blockquote><pre>{@code
616 * MethodHandle invoker = MethodHandles.spreadInvoker(this.type(), 0);
617 * Object result = invoker.invokeExact(this, arguments);
618 * }</pre></blockquote>
619 * <p>
620 * Unlike the signature polymorphic methods {@code invokeExact} and {@code invoke},
621 * {@code invokeWithArguments} can be accessed normally via the Core Reflection API and JNI.
622 * It can therefore be used as a bridge between native or reflective code and method handles.
623 *
624 * @param arguments the arguments to pass to the target
625 * @return the result returned by the target
626 * @throws ClassCastException if an argument cannot be converted by reference casting
627 * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments
628 * @throws Throwable anything thrown by the target method invocation
629 * @see MethodHandles#spreadInvoker
630 */
631 public Object invokeWithArguments(Object... arguments) throws Throwable {
632 MethodType invocationType = MethodType.genericMethodType(arguments == null ? 0 : arguments.length);
633 return invocationType.invokers().spreadInvoker(0).invokeExact(asType(invocationType), arguments);
634 }
635
636 /**
637 * Performs a variable arity invocation, passing the arguments in the given array
638 * to the method handle, as if via an inexact {@link #invoke invoke} from a call site
639 * which mentions only the type {@code Object}, and whose arity is the length
640 * of the argument array.
641 * <p>
642 * This method is also equivalent to the following code:
643 * <blockquote><pre>{@code
644 * invokeWithArguments(arguments.toArray()
645 * }</pre></blockquote>
646 *
647 * @param arguments the arguments to pass to the target
648 * @return the result returned by the target
649 * @throws NullPointerException if {@code arguments} is a null reference
650 * @throws ClassCastException if an argument cannot be converted by reference casting
651 * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments
652 * @throws Throwable anything thrown by the target method invocation
653 */
654 public Object invokeWithArguments(java.util.List<?> arguments) throws Throwable {
655 return invokeWithArguments(arguments.toArray());
656 }
657
658 /**
659 * Produces an adapter method handle which adapts the type of the
660 * current method handle to a new type.
661 * The resulting method handle is guaranteed to report a type
662 * which is equal to the desired new type.
663 * <p>
664 * If the original type and new type are equal, returns {@code this}.
665 * <p>
666 * The new method handle, when invoked, will perform the following
667 * steps:
668 * <ul>
669 * <li>Convert the incoming argument list to match the original
670 * method handle's argument list.
671 * <li>Invoke the original method handle on the converted argument list.
672 * <li>Convert any result returned by the original method handle
673 * to the return type of new method handle.
674 * </ul>
675 * <p>
676 * This method provides the crucial behavioral difference between
677 * {@link #invokeExact invokeExact} and plain, inexact {@link #invoke invoke}.
678 * The two methods
679 * perform the same steps when the caller's type descriptor exactly matches
680 * the callee's, but when the types differ, plain {@link #invoke invoke}
681 * also calls {@code asType} (or some internal equivalent) in order
682 * to match up the caller's and callee's types.
683 * <p>
684 * If the current method is a variable arity method handle
685 * argument list conversion may involve the conversion and collection
686 * of several arguments into an array, as
687 * {@linkplain #asVarargsCollector described elsewhere}.
688 * In every other case, all conversions are applied <em>pairwise</em>,
689 * which means that each argument or return value is converted to
690 * exactly one argument or return value (or no return value).
691 * The applied conversions are defined by consulting the
692 * the corresponding component types of the old and new
693 * method handle types.
694 * <p>
695 * Let <em>T0</em> and <em>T1</em> be corresponding new and old parameter types,
696 * or old and new return types. Specifically, for some valid index {@code i}, let
697 * <em>T0</em>{@code =newType.parameterType(i)} and <em>T1</em>{@code =this.type().parameterType(i)}.
698 * Or else, going the other way for return values, let
699 * <em>T0</em>{@code =this.type().returnType()} and <em>T1</em>{@code =newType.returnType()}.
700 * If the types are the same, the new method handle makes no change
701 * to the corresponding argument or return value (if any).
702 * Otherwise, one of the following conversions is applied
703 * if possible:
704 * <ul>
705 * <li>If <em>T0</em> and <em>T1</em> are references, then a cast to <em>T1</em> is applied.
706 * (The types do not need to be related in any particular way.
707 * This is because a dynamic value of null can convert to any reference type.)
708 * <li>If <em>T0</em> and <em>T1</em> are primitives, then a Java method invocation
709 * conversion (JLS 5.3) is applied, if one exists.
710 * (Specifically, <em>T0</em> must convert to <em>T1</em> by a widening primitive conversion.)
711 * <li>If <em>T0</em> is a primitive and <em>T1</em> a reference,
712 * a Java casting conversion (JLS 5.5) is applied if one exists.
713 * (Specifically, the value is boxed from <em>T0</em> to its wrapper class,
714 * which is then widened as needed to <em>T1</em>.)
715 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
716 * conversion will be applied at runtime, possibly followed
717 * by a Java method invocation conversion (JLS 5.3)
718 * on the primitive value. (These are the primitive widening conversions.)
719 * <em>T0</em> must be a wrapper class or a supertype of one.
720 * (In the case where <em>T0</em> is Object, these are the conversions
721 * allowed by {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}.)
722 * The unboxing conversion must have a possibility of success, which means that
723 * if <em>T0</em> is not itself a wrapper class, there must exist at least one
724 * wrapper class <em>TW</em> which is a subtype of <em>T0</em> and whose unboxed
725 * primitive value can be widened to <em>T1</em>.
726 * <li>If the return type <em>T1</em> is marked as void, any returned value is discarded
727 * <li>If the return type <em>T0</em> is void and <em>T1</em> a reference, a null value is introduced.
728 * <li>If the return type <em>T0</em> is void and <em>T1</em> a primitive,
729 * a zero value is introduced.
730 * </ul>
731 * (<em>Note:</em> Both <em>T0</em> and <em>T1</em> may be regarded as static types,
732 * because neither corresponds specifically to the <em>dynamic type</em> of any
733 * actual argument or return value.)
734 * <p>
735 * The method handle conversion cannot be made if any one of the required
736 * pairwise conversions cannot be made.
737 * <p>
738 * At runtime, the conversions applied to reference arguments
739 * or return values may require additional runtime checks which can fail.
740 * An unboxing operation may fail because the original reference is null,
741 * causing a {@link java.lang.NullPointerException NullPointerException}.
742 * An unboxing operation or a reference cast may also fail on a reference
743 * to an object of the wrong type,
744 * causing a {@link java.lang.ClassCastException ClassCastException}.
745 * Although an unboxing operation may accept several kinds of wrappers,
746 * if none are available, a {@code ClassCastException} will be thrown.
747 *
748 * @param newType the expected type of the new method handle
749 * @return a method handle which delegates to {@code this} after performing
750 * any necessary argument conversions, and arranges for any
751 * necessary return value conversions
752 * @throws NullPointerException if {@code newType} is a null reference
753 * @throws WrongMethodTypeException if the conversion cannot be made
754 * @see MethodHandles#explicitCastArguments
755 */
756 public MethodHandle asType(MethodType newType) {
757 // Fast path alternative to a heavyweight {@code asType} call.
758 // Return 'this' if the conversion will be a no-op.
759 if (newType == type) {
760 return this;
761 }
762 // Return 'this.asTypeCache' if the conversion is already memoized.
763 MethodHandle atc = asTypeCached(newType);
764 if (atc != null) {
765 return atc;
766 }
767 return asTypeUncached(newType);
768 }
769
770 private MethodHandle asTypeCached(MethodType newType) {
771 MethodHandle atc = asTypeCache;
772 if (atc != null && newType == atc.type) {
773 return atc;
774 }
775 return null;
776 }
777
778 /** Override this to change asType behavior. */
779 /*non-public*/ MethodHandle asTypeUncached(MethodType newType) {
780 if (!type.isConvertibleTo(newType))
781 throw new WrongMethodTypeException("cannot convert "+this+" to "+newType);
782 return asTypeCache = MethodHandleImpl.makePairwiseConvert(this, newType, true);
783 }
784
785 /**
786 * Makes an <em>array-spreading</em> method handle, which accepts a trailing array argument
787 * and spreads its elements as positional arguments.
788 * The new method handle adapts, as its <i>target</i>,
789 * the current method handle. The type of the adapter will be
790 * the same as the type of the target, except that the final
791 * {@code arrayLength} parameters of the target's type are replaced
792 * by a single array parameter of type {@code arrayType}.
793 * <p>
794 * If the array element type differs from any of the corresponding
795 * argument types on the original target,
796 * the original target is adapted to take the array elements directly,
797 * as if by a call to {@link #asType asType}.
798 * <p>
799 * When called, the adapter replaces a trailing array argument
800 * by the array's elements, each as its own argument to the target.
801 * (The order of the arguments is preserved.)
802 * They are converted pairwise by casting and/or unboxing
803 * to the types of the trailing parameters of the target.
804 * Finally the target is called.
805 * What the target eventually returns is returned unchanged by the adapter.
806 * <p>
807 * Before calling the target, the adapter verifies that the array
808 * contains exactly enough elements to provide a correct argument count
809 * to the target method handle.
810 * (The array may also be null when zero elements are required.)
811 * <p>
812 * If, when the adapter is called, the supplied array argument does
813 * not have the correct number of elements, the adapter will throw
814 * an {@link IllegalArgumentException} instead of invoking the target.
815 * <p>
816 * Here are some simple examples of array-spreading method handles:
817 * <blockquote><pre>{@code
818 MethodHandle equals = publicLookup()
819 .findVirtual(String.class, "equals", methodType(boolean.class, Object.class));
820 assert( (boolean) equals.invokeExact("me", (Object)"me"));
821 assert(!(boolean) equals.invokeExact("me", (Object)"thee"));
822 // spread both arguments from a 2-array:
823 MethodHandle eq2 = equals.asSpreader(Object[].class, 2);
824 assert( (boolean) eq2.invokeExact(new Object[]{ "me", "me" }));
825 assert(!(boolean) eq2.invokeExact(new Object[]{ "me", "thee" }));
826 // try to spread from anything but a 2-array:
827 for (int n = 0; n <= 10; n++) {
828 Object[] badArityArgs = (n == 2 ? null : new Object[n]);
829 try { assert((boolean) eq2.invokeExact(badArityArgs) && false); }
830 catch (IllegalArgumentException ex) { } // OK
831 }
832 // spread both arguments from a String array:
833 MethodHandle eq2s = equals.asSpreader(String[].class, 2);
834 assert( (boolean) eq2s.invokeExact(new String[]{ "me", "me" }));
835 assert(!(boolean) eq2s.invokeExact(new String[]{ "me", "thee" }));
836 // spread second arguments from a 1-array:
837 MethodHandle eq1 = equals.asSpreader(Object[].class, 1);
838 assert( (boolean) eq1.invokeExact("me", new Object[]{ "me" }));
839 assert(!(boolean) eq1.invokeExact("me", new Object[]{ "thee" }));
840 // spread no arguments from a 0-array or null:
841 MethodHandle eq0 = equals.asSpreader(Object[].class, 0);
842 assert( (boolean) eq0.invokeExact("me", (Object)"me", new Object[0]));
843 assert(!(boolean) eq0.invokeExact("me", (Object)"thee", (Object[])null));
844 // asSpreader and asCollector are approximate inverses:
845 for (int n = 0; n <= 2; n++) {
846 for (Class<?> a : new Class<?>[]{Object[].class, String[].class, CharSequence[].class}) {
847 MethodHandle equals2 = equals.asSpreader(a, n).asCollector(a, n);
848 assert( (boolean) equals2.invokeWithArguments("me", "me"));
849 assert(!(boolean) equals2.invokeWithArguments("me", "thee"));
850 }
851 }
852 MethodHandle caToString = publicLookup()
853 .findStatic(Arrays.class, "toString", methodType(String.class, char[].class));
854 assertEquals("[A, B, C]", (String) caToString.invokeExact("ABC".toCharArray()));
855 MethodHandle caString3 = caToString.asCollector(char[].class, 3);
856 assertEquals("[A, B, C]", (String) caString3.invokeExact('A', 'B', 'C'));
857 MethodHandle caToString2 = caString3.asSpreader(char[].class, 2);
858 assertEquals("[A, B, C]", (String) caToString2.invokeExact('A', "BC".toCharArray()));
859 * }</pre></blockquote>
860 * @param arrayType usually {@code Object[]}, the type of the array argument from which to extract the spread arguments
861 * @param arrayLength the number of arguments to spread from an incoming array argument
862 * @return a new method handle which spreads its final array argument,
863 * before calling the original method handle
864 * @throws NullPointerException if {@code arrayType} is a null reference
865 * @throws IllegalArgumentException if {@code arrayType} is not an array type,
866 * or if target does not have at least
867 * {@code arrayLength} parameter types,
868 * or if {@code arrayLength} is negative,
869 * or if the resulting method handle's type would have
870 * <a href="MethodHandle.html#maxarity">too many parameters</a>
871 * @throws WrongMethodTypeException if the implied {@code asType} call fails
872 * @see #asCollector
873 */
874 public MethodHandle asSpreader(Class<?> arrayType, int arrayLength) {
875 return asSpreader(type().parameterCount() - arrayLength, arrayType, arrayLength);
876 }
877
878 /**
879 * Makes an <em>array-spreading</em> method handle, which accepts an array argument at a given position and spreads
880 * its elements as positional arguments in place of the array. The new method handle adapts, as its <i>target</i>,
881 * the current method handle. The type of the adapter will be the same as the type of the target, except that the
882 * {@code arrayLength} parameters of the target's type, starting at the zero-based position {@code spreadArgPos},
883 * are replaced by a single array parameter of type {@code arrayType}.
884 * <p>
885 * This method behaves very much like {@link #asSpreader(Class, int)}, but accepts an additional {@code spreadArgPos}
886 * argument to indicate at which position in the parameter list the spreading should take place.
887 * <p>
888 * @apiNote Example:
889 * <blockquote><pre>{@code
890 MethodHandle compare = LOOKUP.findStatic(Objects.class, "compare", methodType(int.class, Object.class, Object.class, Comparator.class));
891 MethodHandle compare2FromArray = compare.asSpreader(0, Object[].class, 2);
892 Object[] ints = new Object[]{3, 9, 7, 7};
893 Comparator<Integer> cmp = (a, b) -> a - b;
894 assertTrue((int) compare2FromArray.invoke(Arrays.copyOfRange(ints, 0, 2), cmp) < 0);
895 assertTrue((int) compare2FromArray.invoke(Arrays.copyOfRange(ints, 1, 3), cmp) > 0);
896 assertTrue((int) compare2FromArray.invoke(Arrays.copyOfRange(ints, 2, 4), cmp) == 0);
897 * }</pre></blockquote>
898 * @param spreadArgPos the position (zero-based index) in the argument list at which spreading should start.
899 * @param arrayType usually {@code Object[]}, the type of the array argument from which to extract the spread arguments
900 * @param arrayLength the number of arguments to spread from an incoming array argument
901 * @return a new method handle which spreads an array argument at a given position,
902 * before calling the original method handle
903 * @throws NullPointerException if {@code arrayType} is a null reference
904 * @throws IllegalArgumentException if {@code arrayType} is not an array type,
905 * or if target does not have at least
906 * {@code arrayLength} parameter types,
907 * or if {@code arrayLength} is negative,
908 * or if {@code spreadArgPos} has an illegal value (negative, or together with arrayLength exceeding the
909 * number of arguments),
910 * or if the resulting method handle's type would have
911 * <a href="MethodHandle.html#maxarity">too many parameters</a>
912 * @throws WrongMethodTypeException if the implied {@code asType} call fails
913 *
914 * @see #asSpreader(Class, int)
915 * @since 9
916 */
917 public MethodHandle asSpreader(int spreadArgPos, Class<?> arrayType, int arrayLength) {
918 MethodType postSpreadType = asSpreaderChecks(arrayType, spreadArgPos, arrayLength);
919 MethodHandle afterSpread = this.asType(postSpreadType);
920 BoundMethodHandle mh = afterSpread.rebind();
921 LambdaForm lform = mh.editor().spreadArgumentsForm(1 + spreadArgPos, arrayType, arrayLength);
922 MethodType preSpreadType = postSpreadType.replaceParameterTypes(spreadArgPos, spreadArgPos + arrayLength, arrayType);
923 return mh.copyWith(preSpreadType, lform);
924 }
925
926 /**
927 * See if {@code asSpreader} can be validly called with the given arguments.
928 * Return the type of the method handle call after spreading but before conversions.
929 */
930 private MethodType asSpreaderChecks(Class<?> arrayType, int pos, int arrayLength) {
931 spreadArrayChecks(arrayType, arrayLength);
932 int nargs = type().parameterCount();
933 if (nargs < arrayLength || arrayLength < 0)
934 throw newIllegalArgumentException("bad spread array length");
935 if (pos < 0 || pos + arrayLength > nargs) {
936 throw newIllegalArgumentException("bad spread position");
937 }
938 Class<?> arrayElement = arrayType.getComponentType();
939 MethodType mtype = type();
940 boolean match = true, fail = false;
941 for (int i = pos; i < pos + arrayLength; i++) {
942 Class<?> ptype = mtype.parameterType(i);
943 if (ptype != arrayElement) {
944 match = false;
945 if (!MethodType.canConvert(arrayElement, ptype)) {
946 fail = true;
947 break;
948 }
949 }
950 }
951 if (match) return mtype;
952 MethodType needType = mtype.asSpreaderType(arrayType, pos, arrayLength);
953 if (!fail) return needType;
954 // elicit an error:
955 this.asType(needType);
956 throw newInternalError("should not return", null);
957 }
958
959 private void spreadArrayChecks(Class<?> arrayType, int arrayLength) {
960 Class<?> arrayElement = arrayType.getComponentType();
961 if (arrayElement == null)
962 throw newIllegalArgumentException("not an array type", arrayType);
963 if ((arrayLength & 0x7F) != arrayLength) {
964 if ((arrayLength & 0xFF) != arrayLength)
965 throw newIllegalArgumentException("array length is not legal", arrayLength);
966 assert(arrayLength >= 128);
967 if (arrayElement == long.class ||
968 arrayElement == double.class)
969 throw newIllegalArgumentException("array length is not legal for long[] or double[]", arrayLength);
970 }
971 }
972 /**
973 * Adapts this method handle to be {@linkplain #asVarargsCollector variable arity}
974 * if the boolean flag is true, else {@linkplain #asFixedArity fixed arity}.
975 * If the method handle is already of the proper arity mode, it is returned
976 * unchanged.
977 * <p>This method is sometimes useful when adapting a method handle that
978 * may be variable arity, to ensure that the resulting adapter is also
979 * variable arity if and only if the original handle was. For example,
980 * this code changes the first argument of a handle to {@code int} without
981 * disturbing its variable arity property:
982 * {@code mh.asType(mh.type().changeParameterType(0,int.class)).withVarargs(mh.isVarargsCollector())}
983 * @param makeVarargs true if the return method handle should have variable arity behavior
984 * @return a method handle of the same type, with possibly adjusted variable arity behavior
985 * @throws IllegalArgumentException if {@code makeVarargs} is true and
986 * this method handle does not have a trailing array parameter
987 * @since 9
988 */
989 public MethodHandle withVarargs(boolean makeVarargs) {
990 if (!makeVarargs) {
991 return asFixedArity();
992 } else if (!isVarargsCollector()) {
993 return asVarargsCollector(type().lastParameterType());
994 } else {
995 return this;
996 }
997 }
998
999 /**
1000 * Makes an <em>array-collecting</em> method handle, which accepts a given number of trailing
1001 * positional arguments and collects them into an array argument.
1002 * The new method handle adapts, as its <i>target</i>,
1003 * the current method handle. The type of the adapter will be
1004 * the same as the type of the target, except that a single trailing
1005 * parameter (usually of type {@code arrayType}) is replaced by
1006 * {@code arrayLength} parameters whose type is element type of {@code arrayType}.
1007 * <p>
1008 * If the array type differs from the final argument type on the original target,
1009 * the original target is adapted to take the array type directly,
1010 * as if by a call to {@link #asType asType}.
1011 * <p>
1012 * When called, the adapter replaces its trailing {@code arrayLength}
1013 * arguments by a single new array of type {@code arrayType}, whose elements
1014 * comprise (in order) the replaced arguments.
1015 * Finally the target is called.
1016 * What the target eventually returns is returned unchanged by the adapter.
1017 * <p>
1018 * (The array may also be a shared constant when {@code arrayLength} is zero.)
1019 * <p>
1020 * (<em>Note:</em> The {@code arrayType} is often identical to the last
1021 * parameter type of the original target.
1022 * It is an explicit argument for symmetry with {@code asSpreader}, and also
1023 * to allow the target to use a simple {@code Object} as its last parameter type.)
1024 * <p>
1025 * In order to create a collecting adapter which is not restricted to a particular
1026 * number of collected arguments, use {@link #asVarargsCollector asVarargsCollector}
1027 * or {@link #withVarargs withVarargs} instead.
1028 * <p>
1029 * Here are some examples of array-collecting method handles:
1030 * <blockquote><pre>{@code
1031 MethodHandle deepToString = publicLookup()
1032 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
1033 assertEquals("[won]", (String) deepToString.invokeExact(new Object[]{"won"}));
1034 MethodHandle ts1 = deepToString.asCollector(Object[].class, 1);
1035 assertEquals(methodType(String.class, Object.class), ts1.type());
1036 //assertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"})); //FAIL
1037 assertEquals("[[won]]", (String) ts1.invokeExact((Object) new Object[]{"won"}));
1038 // arrayType can be a subtype of Object[]
1039 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
1040 assertEquals(methodType(String.class, String.class, String.class), ts2.type());
1041 assertEquals("[two, too]", (String) ts2.invokeExact("two", "too"));
1042 MethodHandle ts0 = deepToString.asCollector(Object[].class, 0);
1043 assertEquals("[]", (String) ts0.invokeExact());
1044 // collectors can be nested, Lisp-style
1045 MethodHandle ts22 = deepToString.asCollector(Object[].class, 3).asCollector(String[].class, 2);
1046 assertEquals("[A, B, [C, D]]", ((String) ts22.invokeExact((Object)'A', (Object)"B", "C", "D")));
1047 // arrayType can be any primitive array type
1048 MethodHandle bytesToString = publicLookup()
1049 .findStatic(Arrays.class, "toString", methodType(String.class, byte[].class))
1050 .asCollector(byte[].class, 3);
1051 assertEquals("[1, 2, 3]", (String) bytesToString.invokeExact((byte)1, (byte)2, (byte)3));
1052 MethodHandle longsToString = publicLookup()
1053 .findStatic(Arrays.class, "toString", methodType(String.class, long[].class))
1054 .asCollector(long[].class, 1);
1055 assertEquals("[123]", (String) longsToString.invokeExact((long)123));
1056 * }</pre></blockquote>
1057 * <p>
1058 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
1059 * variable-arity method handle}, even if the original target method handle was.
1060 * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments
1061 * @param arrayLength the number of arguments to collect into a new array argument
1062 * @return a new method handle which collects some trailing argument
1063 * into an array, before calling the original method handle
1064 * @throws NullPointerException if {@code arrayType} is a null reference
1065 * @throws IllegalArgumentException if {@code arrayType} is not an array type
1066 * or {@code arrayType} is not assignable to this method handle's trailing parameter type,
1067 * or {@code arrayLength} is not a legal array size,
1068 * or the resulting method handle's type would have
1069 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1070 * @throws WrongMethodTypeException if the implied {@code asType} call fails
1071 * @see #asSpreader
1072 * @see #asVarargsCollector
1073 */
1074 public MethodHandle asCollector(Class<?> arrayType, int arrayLength) {
1075 return asCollector(type().parameterCount() - 1, arrayType, arrayLength);
1076 }
1077
1078 /**
1079 * Makes an <em>array-collecting</em> method handle, which accepts a given number of positional arguments starting
1080 * at a given position, and collects them into an array argument. The new method handle adapts, as its
1081 * <i>target</i>, the current method handle. The type of the adapter will be the same as the type of the target,
1082 * except that the parameter at the position indicated by {@code collectArgPos} (usually of type {@code arrayType})
1083 * is replaced by {@code arrayLength} parameters whose type is element type of {@code arrayType}.
1084 * <p>
1085 * This method behaves very much like {@link #asCollector(Class, int)}, but differs in that its {@code
1086 * collectArgPos} argument indicates at which position in the parameter list arguments should be collected. This
1087 * index is zero-based.
1088 * <p>
1089 * @apiNote Examples:
1090 * <blockquote><pre>{@code
1091 StringWriter swr = new StringWriter();
1092 MethodHandle swWrite = LOOKUP.findVirtual(StringWriter.class, "write", methodType(void.class, char[].class, int.class, int.class)).bindTo(swr);
1093 MethodHandle swWrite4 = swWrite.asCollector(0, char[].class, 4);
1094 swWrite4.invoke('A', 'B', 'C', 'D', 1, 2);
1095 assertEquals("BC", swr.toString());
1096 swWrite4.invoke('P', 'Q', 'R', 'S', 0, 4);
1097 assertEquals("BCPQRS", swr.toString());
1098 swWrite4.invoke('W', 'X', 'Y', 'Z', 3, 1);
1099 assertEquals("BCPQRSZ", swr.toString());
1100 * }</pre></blockquote>
1101 * <p>
1102 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
1103 * variable-arity method handle}, even if the original target method handle was.
1104 * @param collectArgPos the zero-based position in the parameter list at which to start collecting.
1105 * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments
1106 * @param arrayLength the number of arguments to collect into a new array argument
1107 * @return a new method handle which collects some arguments
1108 * into an array, before calling the original method handle
1109 * @throws NullPointerException if {@code arrayType} is a null reference
1110 * @throws IllegalArgumentException if {@code arrayType} is not an array type
1111 * or {@code arrayType} is not assignable to this method handle's array parameter type,
1112 * or {@code arrayLength} is not a legal array size,
1113 * or {@code collectArgPos} has an illegal value (negative, or greater than the number of arguments),
1114 * or the resulting method handle's type would have
1115 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1116 * @throws WrongMethodTypeException if the implied {@code asType} call fails
1117 *
1118 * @see #asCollector(Class, int)
1119 * @since 9
1120 */
1121 public MethodHandle asCollector(int collectArgPos, Class<?> arrayType, int arrayLength) {
1122 asCollectorChecks(arrayType, collectArgPos, arrayLength);
1123 BoundMethodHandle mh = rebind();
1124 MethodType resultType = type().asCollectorType(arrayType, collectArgPos, arrayLength);
1125 MethodHandle newArray = MethodHandleImpl.varargsArray(arrayType, arrayLength);
1126 LambdaForm lform = mh.editor().collectArgumentArrayForm(1 + collectArgPos, newArray);
1127 if (lform != null) {
1128 return mh.copyWith(resultType, lform);
1129 }
1130 lform = mh.editor().collectArgumentsForm(1 + collectArgPos, newArray.type().basicType());
1131 return mh.copyWithExtendL(resultType, lform, newArray);
1132 }
1133
1134 /**
1135 * See if {@code asCollector} can be validly called with the given arguments.
1136 * Return false if the last parameter is not an exact match to arrayType.
1137 */
1138 /*non-public*/ boolean asCollectorChecks(Class<?> arrayType, int pos, int arrayLength) {
1139 spreadArrayChecks(arrayType, arrayLength);
1140 int nargs = type().parameterCount();
1141 if (pos < 0 || pos >= nargs) {
1142 throw newIllegalArgumentException("bad collect position");
1143 }
1144 if (nargs != 0) {
1145 Class<?> param = type().parameterType(pos);
1146 if (param == arrayType) return true;
1147 if (param.isAssignableFrom(arrayType)) return false;
1148 }
1149 throw newIllegalArgumentException("array type not assignable to argument", this, arrayType);
1150 }
1151
1152 /**
1153 * Makes a <em>variable arity</em> adapter which is able to accept
1154 * any number of trailing positional arguments and collect them
1155 * into an array argument.
1156 * <p>
1157 * The type and behavior of the adapter will be the same as
1158 * the type and behavior of the target, except that certain
1159 * {@code invoke} and {@code asType} requests can lead to
1160 * trailing positional arguments being collected into target's
1161 * trailing parameter.
1162 * Also, the last parameter type of the adapter will be
1163 * {@code arrayType}, even if the target has a different
1164 * last parameter type.
1165 * <p>
1166 * This transformation may return {@code this} if the method handle is
1167 * already of variable arity and its trailing parameter type
1168 * is identical to {@code arrayType}.
1169 * <p>
1170 * When called with {@link #invokeExact invokeExact}, the adapter invokes
1171 * the target with no argument changes.
1172 * (<em>Note:</em> This behavior is different from a
1173 * {@linkplain #asCollector fixed arity collector},
1174 * since it accepts a whole array of indeterminate length,
1175 * rather than a fixed number of arguments.)
1176 * <p>
1177 * When called with plain, inexact {@link #invoke invoke}, if the caller
1178 * type is the same as the adapter, the adapter invokes the target as with
1179 * {@code invokeExact}.
1180 * (This is the normal behavior for {@code invoke} when types match.)
1181 * <p>
1182 * Otherwise, if the caller and adapter arity are the same, and the
1183 * trailing parameter type of the caller is a reference type identical to
1184 * or assignable to the trailing parameter type of the adapter,
1185 * the arguments and return values are converted pairwise,
1186 * as if by {@link #asType asType} on a fixed arity
1187 * method handle.
1188 * <p>
1189 * Otherwise, the arities differ, or the adapter's trailing parameter
1190 * type is not assignable from the corresponding caller type.
1191 * In this case, the adapter replaces all trailing arguments from
1192 * the original trailing argument position onward, by
1193 * a new array of type {@code arrayType}, whose elements
1194 * comprise (in order) the replaced arguments.
1195 * <p>
1196 * The caller type must provides as least enough arguments,
1197 * and of the correct type, to satisfy the target's requirement for
1198 * positional arguments before the trailing array argument.
1199 * Thus, the caller must supply, at a minimum, {@code N-1} arguments,
1200 * where {@code N} is the arity of the target.
1201 * Also, there must exist conversions from the incoming arguments
1202 * to the target's arguments.
1203 * As with other uses of plain {@code invoke}, if these basic
1204 * requirements are not fulfilled, a {@code WrongMethodTypeException}
1205 * may be thrown.
1206 * <p>
1207 * In all cases, what the target eventually returns is returned unchanged by the adapter.
1208 * <p>
1209 * In the final case, it is exactly as if the target method handle were
1210 * temporarily adapted with a {@linkplain #asCollector fixed arity collector}
1211 * to the arity required by the caller type.
1212 * (As with {@code asCollector}, if the array length is zero,
1213 * a shared constant may be used instead of a new array.
1214 * If the implied call to {@code asCollector} would throw
1215 * an {@code IllegalArgumentException} or {@code WrongMethodTypeException},
1216 * the call to the variable arity adapter must throw
1217 * {@code WrongMethodTypeException}.)
1218 * <p>
1219 * The behavior of {@link #asType asType} is also specialized for
1220 * variable arity adapters, to maintain the invariant that
1221 * plain, inexact {@code invoke} is always equivalent to an {@code asType}
1222 * call to adjust the target type, followed by {@code invokeExact}.
1223 * Therefore, a variable arity adapter responds
1224 * to an {@code asType} request by building a fixed arity collector,
1225 * if and only if the adapter and requested type differ either
1226 * in arity or trailing argument type.
1227 * The resulting fixed arity collector has its type further adjusted
1228 * (if necessary) to the requested type by pairwise conversion,
1229 * as if by another application of {@code asType}.
1230 * <p>
1231 * When a method handle is obtained by executing an {@code ldc} instruction
1232 * of a {@code CONSTANT_MethodHandle} constant, and the target method is marked
1233 * as a variable arity method (with the modifier bit {@code 0x0080}),
1234 * the method handle will accept multiple arities, as if the method handle
1235 * constant were created by means of a call to {@code asVarargsCollector}.
1236 * <p>
1237 * In order to create a collecting adapter which collects a predetermined
1238 * number of arguments, and whose type reflects this predetermined number,
1239 * use {@link #asCollector asCollector} instead.
1240 * <p>
1241 * No method handle transformations produce new method handles with
1242 * variable arity, unless they are documented as doing so.
1243 * Therefore, besides {@code asVarargsCollector} and {@code withVarargs},
1244 * all methods in {@code MethodHandle} and {@code MethodHandles}
1245 * will return a method handle with fixed arity,
1246 * except in the cases where they are specified to return their original
1247 * operand (e.g., {@code asType} of the method handle's own type).
1248 * <p>
1249 * Calling {@code asVarargsCollector} on a method handle which is already
1250 * of variable arity will produce a method handle with the same type and behavior.
1251 * It may (or may not) return the original variable arity method handle.
1252 * <p>
1253 * Here is an example, of a list-making variable arity method handle:
1254 * <blockquote><pre>{@code
1255 MethodHandle deepToString = publicLookup()
1256 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
1257 MethodHandle ts1 = deepToString.asVarargsCollector(Object[].class);
1258 assertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"}));
1259 assertEquals("[won]", (String) ts1.invoke( new Object[]{"won"}));
1260 assertEquals("[won]", (String) ts1.invoke( "won" ));
1261 assertEquals("[[won]]", (String) ts1.invoke((Object) new Object[]{"won"}));
1262 // findStatic of Arrays.asList(...) produces a variable arity method handle:
1263 MethodHandle asList = publicLookup()
1264 .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class));
1265 assertEquals(methodType(List.class, Object[].class), asList.type());
1266 assert(asList.isVarargsCollector());
1267 assertEquals("[]", asList.invoke().toString());
1268 assertEquals("[1]", asList.invoke(1).toString());
1269 assertEquals("[two, too]", asList.invoke("two", "too").toString());
1270 String[] argv = { "three", "thee", "tee" };
1271 assertEquals("[three, thee, tee]", asList.invoke(argv).toString());
1272 assertEquals("[three, thee, tee]", asList.invoke((Object[])argv).toString());
1273 List ls = (List) asList.invoke((Object)argv);
1274 assertEquals(1, ls.size());
1275 assertEquals("[three, thee, tee]", Arrays.toString((Object[])ls.get(0)));
1276 * }</pre></blockquote>
1277 * <p style="font-size:smaller;">
1278 * <em>Discussion:</em>
1279 * These rules are designed as a dynamically-typed variation
1280 * of the Java rules for variable arity methods.
1281 * In both cases, callers to a variable arity method or method handle
1282 * can either pass zero or more positional arguments, or else pass
1283 * pre-collected arrays of any length. Users should be aware of the
1284 * special role of the final argument, and of the effect of a
1285 * type match on that final argument, which determines whether
1286 * or not a single trailing argument is interpreted as a whole
1287 * array or a single element of an array to be collected.
1288 * Note that the dynamic type of the trailing argument has no
1289 * effect on this decision, only a comparison between the symbolic
1290 * type descriptor of the call site and the type descriptor of the method handle.)
1291 *
1292 * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments
1293 * @return a new method handle which can collect any number of trailing arguments
1294 * into an array, before calling the original method handle
1295 * @throws NullPointerException if {@code arrayType} is a null reference
1296 * @throws IllegalArgumentException if {@code arrayType} is not an array type
1297 * or {@code arrayType} is not assignable to this method handle's trailing parameter type
1298 * @see #asCollector
1299 * @see #isVarargsCollector
1300 * @see #withVarargs
1301 * @see #asFixedArity
1302 */
1303 public MethodHandle asVarargsCollector(Class<?> arrayType) {
1304 Objects.requireNonNull(arrayType);
1305 boolean lastMatch = asCollectorChecks(arrayType, type().parameterCount() - 1, 0);
1306 if (isVarargsCollector() && lastMatch)
1307 return this;
1308 return MethodHandleImpl.makeVarargsCollector(this, arrayType);
1309 }
1310
1311 /**
1312 * Determines if this method handle
1313 * supports {@linkplain #asVarargsCollector variable arity} calls.
1314 * Such method handles arise from the following sources:
1315 * <ul>
1316 * <li>a call to {@linkplain #asVarargsCollector asVarargsCollector}
1317 * <li>a call to a {@linkplain java.lang.invoke.MethodHandles.Lookup lookup method}
1318 * which resolves to a variable arity Java method or constructor
1319 * <li>an {@code ldc} instruction of a {@code CONSTANT_MethodHandle}
1320 * which resolves to a variable arity Java method or constructor
1321 * </ul>
1322 * @return true if this method handle accepts more than one arity of plain, inexact {@code invoke} calls
1323 * @see #asVarargsCollector
1324 * @see #asFixedArity
1325 */
1326 public boolean isVarargsCollector() {
1327 return false;
1328 }
1329
1330 /**
1331 * Makes a <em>fixed arity</em> method handle which is otherwise
1332 * equivalent to the current method handle.
1333 * <p>
1334 * If the current method handle is not of
1335 * {@linkplain #asVarargsCollector variable arity},
1336 * the current method handle is returned.
1337 * This is true even if the current method handle
1338 * could not be a valid input to {@code asVarargsCollector}.
1339 * <p>
1340 * Otherwise, the resulting fixed-arity method handle has the same
1341 * type and behavior of the current method handle,
1342 * except that {@link #isVarargsCollector isVarargsCollector}
1343 * will be false.
1344 * The fixed-arity method handle may (or may not) be the
1345 * a previous argument to {@code asVarargsCollector}.
1346 * <p>
1347 * Here is an example, of a list-making variable arity method handle:
1348 * <blockquote><pre>{@code
1349 MethodHandle asListVar = publicLookup()
1350 .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class))
1351 .asVarargsCollector(Object[].class);
1352 MethodHandle asListFix = asListVar.asFixedArity();
1353 assertEquals("[1]", asListVar.invoke(1).toString());
1354 Exception caught = null;
1355 try { asListFix.invoke((Object)1); }
1356 catch (Exception ex) { caught = ex; }
1357 assert(caught instanceof ClassCastException);
1358 assertEquals("[two, too]", asListVar.invoke("two", "too").toString());
1359 try { asListFix.invoke("two", "too"); }
1360 catch (Exception ex) { caught = ex; }
1361 assert(caught instanceof WrongMethodTypeException);
1362 Object[] argv = { "three", "thee", "tee" };
1363 assertEquals("[three, thee, tee]", asListVar.invoke(argv).toString());
1364 assertEquals("[three, thee, tee]", asListFix.invoke(argv).toString());
1365 assertEquals(1, ((List) asListVar.invoke((Object)argv)).size());
1366 assertEquals("[three, thee, tee]", asListFix.invoke((Object)argv).toString());
1367 * }</pre></blockquote>
1368 *
1369 * @return a new method handle which accepts only a fixed number of arguments
1370 * @see #asVarargsCollector
1371 * @see #isVarargsCollector
1372 * @see #withVarargs
1373 */
1374 public MethodHandle asFixedArity() {
1375 assert(!isVarargsCollector());
1376 return this;
1377 }
1378
1379 /**
1380 * Binds a value {@code x} to the first argument of a method handle, without invoking it.
1381 * The new method handle adapts, as its <i>target</i>,
1382 * the current method handle by binding it to the given argument.
1383 * The type of the bound handle will be
1384 * the same as the type of the target, except that a single leading
1385 * reference parameter will be omitted.
1386 * <p>
1387 * When called, the bound handle inserts the given value {@code x}
1388 * as a new leading argument to the target. The other arguments are
1389 * also passed unchanged.
1390 * What the target eventually returns is returned unchanged by the bound handle.
1391 * <p>
1392 * The reference {@code x} must be convertible to the first parameter
1393 * type of the target.
1394 * <p>
1395 * <em>Note:</em> Because method handles are immutable, the target method handle
1396 * retains its original type and behavior.
1397 * <p>
1398 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
1399 * variable-arity method handle}, even if the original target method handle was.
1400 * @param x the value to bind to the first argument of the target
1401 * @return a new method handle which prepends the given value to the incoming
1402 * argument list, before calling the original method handle
1403 * @throws IllegalArgumentException if the target does not have a
1404 * leading parameter type that is a reference type
1405 * @throws ClassCastException if {@code x} cannot be converted
1406 * to the leading parameter type of the target
1407 * @see MethodHandles#insertArguments
1408 */
1409 public MethodHandle bindTo(Object x) {
1410 x = type.leadingReferenceParameter().cast(x); // throw CCE if needed
1411 return bindArgumentL(0, x);
1412 }
1413
1414 /**
1415 * Returns a string representation of the method handle,
1416 * starting with the string {@code "MethodHandle"} and
1417 * ending with the string representation of the method handle's type.
1418 * In other words, this method returns a string equal to the value of:
1419 * <blockquote><pre>{@code
1420 * "MethodHandle" + type().toString()
1421 * }</pre></blockquote>
1422 * <p>
1423 * (<em>Note:</em> Future releases of this API may add further information
1424 * to the string representation.
1425 * Therefore, the present syntax should not be parsed by applications.)
1426 *
1427 * @return a string representation of the method handle
1428 */
1429 @Override
1430 public String toString() {
1431 if (DEBUG_METHOD_HANDLE_NAMES) return "MethodHandle"+debugString();
1432 return standardString();
1433 }
1434 String standardString() {
1435 return "MethodHandle"+type;
1436 }
1437 /** Return a string with a several lines describing the method handle structure.
1438 * This string would be suitable for display in an IDE debugger.
1439 */
1440 String debugString() {
1441 return type+" : "+internalForm()+internalProperties();
1442 }
1443
1444 //// Implementation methods.
1445 //// Sub-classes can override these default implementations.
1446 //// All these methods assume arguments are already validated.
1447
1448 // Other transforms to do: convert, explicitCast, permute, drop, filter, fold, GWT, catch
1449
1450 BoundMethodHandle bindArgumentL(int pos, Object value) {
1451 return rebind().bindArgumentL(pos, value);
1452 }
1453
1454 /*non-public*/
1455 MethodHandle setVarargs(MemberName member) throws IllegalAccessException {
1456 if (!member.isVarargs()) return this;
1457 try {
1458 return this.withVarargs(true);
1459 } catch (IllegalArgumentException ex) {
1460 throw member.makeAccessException("cannot make variable arity", null);
1461 }
1462 }
1463
1464 /*non-public*/
1465 MethodHandle viewAsType(MethodType newType, boolean strict) {
1466 // No actual conversions, just a new view of the same method.
1467 // Note that this operation must not produce a DirectMethodHandle,
1468 // because retyped DMHs, like any transformed MHs,
1469 // cannot be cracked into MethodHandleInfo.
1470 assert viewAsTypeChecks(newType, strict);
1471 BoundMethodHandle mh = rebind();
1472 return mh.copyWith(newType, mh.form);
1473 }
1474
1475 /*non-public*/
1476 boolean viewAsTypeChecks(MethodType newType, boolean strict) {
1477 if (strict) {
1478 assert(type().isViewableAs(newType, true))
1479 : Arrays.asList(this, newType);
1480 } else {
1481 assert(type().basicType().isViewableAs(newType.basicType(), true))
1482 : Arrays.asList(this, newType);
1483 }
1484 return true;
1485 }
1486
1487 // Decoding
1488
1489 /*non-public*/
1490 LambdaForm internalForm() {
1491 return form;
1492 }
1493
1494 /*non-public*/
1495 MemberName internalMemberName() {
1496 return null; // DMH returns DMH.member
1497 }
1498
1499 /*non-public*/
1500 Class<?> internalCallerClass() {
1501 return null; // caller-bound MH for @CallerSensitive method returns caller
1502 }
1503
1504 /*non-public*/
1505 MethodHandleImpl.Intrinsic intrinsicName() {
1506 // no special intrinsic meaning to most MHs
1507 return MethodHandleImpl.Intrinsic.NONE;
1508 }
1509
1510 /*non-public*/
1511 MethodHandle withInternalMemberName(MemberName member, boolean isInvokeSpecial) {
1512 if (member != null) {
1513 return MethodHandleImpl.makeWrappedMember(this, member, isInvokeSpecial);
1514 } else if (internalMemberName() == null) {
1515 // The required internaMemberName is null, and this MH (like most) doesn't have one.
1516 return this;
1517 } else {
1518 // The following case is rare. Mask the internalMemberName by wrapping the MH in a BMH.
1519 MethodHandle result = rebind();
1520 assert (result.internalMemberName() == null);
1521 return result;
1522 }
1523 }
1524
1525 /*non-public*/
1526 boolean isInvokeSpecial() {
1527 return false; // DMH.Special returns true
1528 }
1529
1530 /*non-public*/
1531 Object internalValues() {
1532 return null;
1533 }
1534
1535 /*non-public*/
1536 Object internalProperties() {
1537 // Override to something to follow this.form, like "\n& FOO=bar"
1538 return "";
1539 }
1540
1541 //// Method handle implementation methods.
1542 //// Sub-classes can override these default implementations.
1543 //// All these methods assume arguments are already validated.
1544
1545 /*non-public*/
1546 abstract MethodHandle copyWith(MethodType mt, LambdaForm lf);
1547
1548 /** Require this method handle to be a BMH, or else replace it with a "wrapper" BMH.
1549 * Many transforms are implemented only for BMHs.
1550 * @return a behaviorally equivalent BMH
1551 */
1552 abstract BoundMethodHandle rebind();
1553
1554 /**
1555 * Replace the old lambda form of this method handle with a new one.
1556 * The new one must be functionally equivalent to the old one.
1557 * Threads may continue running the old form indefinitely,
1558 * but it is likely that the new one will be preferred for new executions.
1559 * Use with discretion.
1560 */
1561 /*non-public*/
1562 void updateForm(LambdaForm newForm) {
1563 assert(newForm.customized == null || newForm.customized == this);
1564 if (form == newForm) return;
1565 newForm.prepare(); // as in MethodHandle.<init>
1566 UNSAFE.putObject(this, FORM_OFFSET, newForm);
1567 UNSAFE.fullFence();
1568 }
1569
1570 /** Craft a LambdaForm customized for this particular MethodHandle */
1571 /*non-public*/
1572 void customize() {
1573 if (form.customized == null) {
1574 LambdaForm newForm = form.customize(this);
1575 updateForm(newForm);
1576 } else {
1577 assert(form.customized == this);
1578 }
1579 }
1580
1581 private static final long FORM_OFFSET;
1582 static {
1583 try {
1584 FORM_OFFSET = UNSAFE.objectFieldOffset(MethodHandle.class.getDeclaredField("form"));
1585 } catch (ReflectiveOperationException ex) {
1586 throw newInternalError(ex);
1587 }
1588 }
1589 }