18b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath/* 28b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved. 38b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 48b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 58b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This code is free software; you can redistribute it and/or modify it 68b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * under the terms of the GNU General Public License version 2 only, as 78b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * published by the Free Software Foundation. Oracle designates this 88b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * particular file as subject to the "Classpath" exception as provided 98b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * by Oracle in the LICENSE file that accompanied this code. 108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This code is distributed in the hope that it will be useful, but WITHOUT 128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * version 2 for more details (a copy is included in the LICENSE file that 158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * accompanied this code). 168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * You should have received a copy of the GNU General Public License version 188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 2 along with this work; if not, write to the Free Software Foundation, 198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or visit www.oracle.com if you need additional information or have any 238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * questions. 248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathpackage java.lang.invoke; 278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 29faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamathimport dalvik.system.EmulatedStackFrame; 308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathimport static java.lang.invoke.MethodHandleStatics.*; 328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath/** 348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A method handle is a typed, directly executable reference to an underlying method, 358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * constructor, field, or similar low-level operation, with optional 368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * transformations of arguments or return values. 378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * These transformations are quite general, and include such patterns as 388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@linkplain #asType conversion}, 398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@linkplain #bindTo insertion}, 406774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * {@linkplain java.lang.invoke.MethodHandles#dropArguments deletion}, 41f4ee5c6dccff8f7e037f95b26767e552ea93d41bNarayan Kamath * and {@linkplain java.lang.invoke.MethodHandles#filterArguments substitution}. 428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Method handle contents</h1> 448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Method handles are dynamically and strongly typed according to their parameter and return types. 458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * They are not distinguished by the name or the defining class of their underlying methods. 468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A method handle must be invoked using a symbolic type descriptor which matches 478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the method handle's own {@linkplain #type type descriptor}. 488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Every method handle reports its type descriptor via the {@link #type type} accessor. 508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This type descriptor is a {@link java.lang.invoke.MethodType MethodType} object, 518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * whose structure is a series of classes, one of which is 528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the return type of the method (or {@code void.class} if none). 538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A method handle's type controls the types of invocations it accepts, 558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and the kinds of transformations that apply to it. 568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A method handle contains a pair of special invoker methods 588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * called {@link #invokeExact invokeExact} and {@link #invoke invoke}. 598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Both invoker methods provide direct access to the method handle's 608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * underlying method, constructor, field, or other operation, 618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as modified by transformations of arguments and return values. 628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Both invokers accept calls which exactly match the method handle's own type. 638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The plain, inexact invoker also accepts a range of other call types. 648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Method handles are immutable and have no visible state. 668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Of course, they can be bound to underlying methods or data which exhibit state. 678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * With respect to the Java Memory Model, any method handle will behave 688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as if all of its (internal) fields are final variables. This means that any method 698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * handle made visible to the application will always be fully formed. 708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This is true even if the method handle is published through a shared 718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * variable in a data race. 728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Method handles cannot be subclassed by the user. 748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Implementations may (or may not) create internal subclasses of {@code MethodHandle} 758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which may be visible via the {@link java.lang.Object#getClass Object.getClass} 768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * operation. The programmer should not draw conclusions about a method handle 778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * from its specific class, as the method handle class hierarchy (if any) 788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * may change from time to time or across implementations from different vendors. 798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Method handle compilation</h1> 818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A Java method call expression naming {@code invokeExact} or {@code invoke} 828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * can invoke a method handle from Java source code. 838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * From the viewpoint of source code, these methods can take any arguments 848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and their result can be cast to any return type. 858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Formally this is accomplished by giving the invoker methods 868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code Object} return types and variable arity {@code Object} arguments, 878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * but they have an additional quality called <em>signature polymorphism</em> 888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which connects this freedom of invocation directly to the JVM execution stack. 898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As is usual with virtual methods, source-level calls to {@code invokeExact} 918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and {@code invoke} compile to an {@code invokevirtual} instruction. 928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * More unusually, the compiler must record the actual argument types, 938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and may not perform method invocation conversions on the arguments. 948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Instead, it must push them on the stack according to their own unconverted types. 958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The method handle object itself is pushed on the stack before the arguments. 968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The compiler then calls the method handle with a symbolic type descriptor which 978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * describes the argument and return types. 988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * To issue a complete symbolic type descriptor, the compiler must also determine 1008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the return type. This is based on a cast on the method invocation expression, 1018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * if there is one, or else {@code Object} if the invocation is an expression 1028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or else {@code void} if the invocation is a statement. 1038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The cast may be to a primitive type (but not {@code void}). 1048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As a corner case, an uncasted {@code null} argument is given 1068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a symbolic type descriptor of {@code java.lang.Void}. 1078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The ambiguity with the type {@code Void} is harmless, since there are no references of type 1088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code Void} except the null reference. 1098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 1108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Method handle invocation</h1> 1118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The first time a {@code invokevirtual} instruction is executed 1128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * it is linked, by symbolically resolving the names in the instruction 1138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and verifying that the method call is statically legal. 1148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This is true of calls to {@code invokeExact} and {@code invoke}. 1158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In this case, the symbolic type descriptor emitted by the compiler is checked for 1168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * correct syntax and names it contains are resolved. 1178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Thus, an {@code invokevirtual} instruction which invokes 1188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a method handle will always link, as long 1198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as the symbolic type descriptor is syntactically well-formed 1208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and the types exist. 1218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When the {@code invokevirtual} is executed after linking, 1238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the receiving method handle's type is first checked by the JVM 1248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to ensure that it matches the symbolic type descriptor. 1258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the type match fails, it means that the method which the 1268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * caller is invoking is not present on the individual 1278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * method handle being invoked. 1288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In the case of {@code invokeExact}, the type descriptor of the invocation 1308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (after resolving symbolic type names) must exactly match the method type 1318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of the receiving method handle. 1328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In the case of plain, inexact {@code invoke}, the resolved type descriptor 1338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * must be a valid argument to the receiver's {@link #asType asType} method. 1348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Thus, plain {@code invoke} is more permissive than {@code invokeExact}. 1358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * After type matching, a call to {@code invokeExact} directly 1378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and immediately invoke the method handle's underlying method 1388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (or other behavior, as the case may be). 1398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A call to plain {@code invoke} works the same as a call to 1418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code invokeExact}, if the symbolic type descriptor specified by the caller 1428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * exactly matches the method handle's own type. 1438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If there is a type mismatch, {@code invoke} attempts 1448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to adjust the type of the receiving method handle, 1458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as if by a call to {@link #asType asType}, 1468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to obtain an exactly invokable method handle {@code M2}. 1478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This allows a more powerful negotiation of method type 1488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * between caller and callee. 1498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (<em>Note:</em> The adjusted method handle {@code M2} is not directly observable, 1518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and implementations are therefore not required to materialize it.) 1528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 1538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Invocation checking</h1> 1548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In typical programs, method handle type matching will usually succeed. 1558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * But if a match fails, the JVM will throw a {@link WrongMethodTypeException}, 1568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * either directly (in the case of {@code invokeExact}) or indirectly as if 1578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * by a failed call to {@code asType} (in the case of {@code invoke}). 1588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Thus, a method type mismatch which might show up as a linkage error 1608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * in a statically typed program can show up as 1618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a dynamic {@code WrongMethodTypeException} 1628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * in a program which uses method handles. 1638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Because method types contain "live" {@code Class} objects, 1658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * method type matching takes into account both types names and class loaders. 1668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Thus, even if a method handle {@code M} is created in one 1678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * class loader {@code L1} and used in another {@code L2}, 1688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * method handle calls are type-safe, because the caller's symbolic type 1698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * descriptor, as resolved in {@code L2}, 1708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * is matched against the original callee method's symbolic type descriptor, 1718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as resolved in {@code L1}. 1728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The resolution in {@code L1} happens when {@code M} is created 1738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and its type is assigned, while the resolution in {@code L2} happens 1748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * when the {@code invokevirtual} instruction is linked. 1758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Apart from the checking of type descriptors, 1778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a method handle's capability to call its underlying method is unrestricted. 1788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If a method handle is formed on a non-public method by a class 1798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * that has access to that method, the resulting handle can be used 1808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * in any place by any caller who receives a reference to it. 1818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Unlike with the Core Reflection API, where access is checked every time 1838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a reflective method is invoked, 1848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * method handle access checking is performed 1858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <a href="MethodHandles.Lookup.html#access">when the method handle is created</a>. 1868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In the case of {@code ldc} (see below), access checking is performed as part of linking 1878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the constant pool entry underlying the constant method handle. 1888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 1898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Thus, handles to non-public methods, or to methods in non-public classes, 1908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * should generally be kept secret. 1918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * They should not be passed to untrusted code unless their use from 1928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the untrusted code would be harmless. 1938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 1948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Method handle creation</h1> 1958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Java code can create a method handle that directly accesses 1968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * any method, constructor, or field that is accessible to that code. 1978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This is done via a reflective, capability-based API called 1986774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * {@link java.lang.invoke.MethodHandles.Lookup MethodHandles.Lookup} 1998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * For example, a static method handle can be obtained 2006774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * from {@link java.lang.invoke.MethodHandles.Lookup#findStatic Lookup.findStatic}. 2018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * There are also conversion methods from Core Reflection API objects, 2026774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * such as {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}. 2038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 2048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Like classes and strings, method handles that correspond to accessible 2058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * fields, methods, and constructors can also be represented directly 2068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * in a class file's constant pool as constants to be loaded by {@code ldc} bytecodes. 2078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A new type of constant pool entry, {@code CONSTANT_MethodHandle}, 2088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * refers directly to an associated {@code CONSTANT_Methodref}, 2098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code CONSTANT_InterfaceMethodref}, or {@code CONSTANT_Fieldref} 2108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * constant pool entry. 2118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (For full details on method handle constants, 2128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * see sections 4.4.8 and 5.4.3.5 of the Java Virtual Machine Specification.) 2138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 2148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Method handles produced by lookups or constant loads from methods or 2158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * constructors with the variable arity modifier bit ({@code 0x0080}) 2168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * have a corresponding variable arity, as if they were defined with 2178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the help of {@link #asVarargsCollector asVarargsCollector}. 2188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 2198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A method reference may refer either to a static or non-static method. 2208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In the non-static case, the method handle type includes an explicit 2218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * receiver argument, prepended before any other arguments. 2228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In the method handle's type, the initial receiver argument is typed 2238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * according to the class under which the method was initially requested. 2248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (E.g., if a non-static method handle is obtained via {@code ldc}, 2258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the type of the receiver is the class named in the constant pool entry.) 2268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 2278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Method handle constants are subject to the same link-time access checks 2288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * their corresponding bytecode instructions, and the {@code ldc} instruction 2298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * will throw corresponding linkage errors if the bytecode behaviors would 2308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * throw such errors. 2318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 2328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As a corollary of this, access to protected members is restricted 2338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to receivers only of the accessing class, or one of its subclasses, 2348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and the accessing class must in turn be a subclass (or package sibling) 2358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of the protected member's defining class. 2368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If a method reference refers to a protected non-static method or field 2378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of a class outside the current package, the receiver argument will 2388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * be narrowed to the type of the accessing class. 2398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 2408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When a method handle to a virtual method is invoked, the method is 2418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * always looked up in the receiver (that is, the first argument). 2428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 2438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A non-virtual method handle to a specific virtual method implementation 2448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * can also be created. These do not perform virtual lookup based on 2458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * receiver type. Such a method handle simulates the effect of 2468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * an {@code invokespecial} instruction to the same method. 2478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 2488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Usage examples</h1> 2498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Here are some examples of usage: 2508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 2518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathObject x, y; String s; int i; 2528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodType mt; MethodHandle mh; 2538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandles.Lookup lookup = MethodHandles.lookup(); 2548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// mt is (char,char)String 2558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmt = MethodType.methodType(String.class, char.class, char.class); 2568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmh = lookup.findVirtual(String.class, "replace", mt); 2578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamaths = (String) mh.invokeExact("daddy",'d','n'); 2588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// invokeExact(Ljava/lang/String;CC)Ljava/lang/String; 2598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(s, "nanny"); 2608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// weakly typed invocation (using MHs.invoke) 2618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamaths = (String) mh.invokeWithArguments("sappy", 'p', 'v'); 2628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(s, "savvy"); 2638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// mt is (Object[])List 2648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmt = MethodType.methodType(java.util.List.class, Object[].class); 2658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmh = lookup.findStatic(java.util.Arrays.class, "asList", mt); 2668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(mh.isVarargsCollector()); 2678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathx = mh.invoke("one", "two"); 2688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// invoke(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/Object; 2698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(x, java.util.Arrays.asList("one","two")); 2708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// mt is (Object,Object,Object)Object 2718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmt = MethodType.genericMethodType(3); 2728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmh = mh.asType(mt); 2738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathx = mh.invokeExact((Object)1, (Object)2, (Object)3); 2748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// invokeExact(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object; 2758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(x, java.util.Arrays.asList(1,2,3)); 2768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// mt is ()int 2778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmt = MethodType.methodType(int.class); 2788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmh = lookup.findVirtual(java.util.List.class, "size", mt); 2798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathi = (int) mh.invokeExact(java.util.Arrays.asList(1,2,3)); 2808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// invokeExact(Ljava/util/List;)I 2818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(i == 3); 2828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmt = MethodType.methodType(void.class, String.class); 2838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmh = lookup.findVirtual(java.io.PrintStream.class, "println", mt); 2848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathmh.invokeExact(System.out, "Hello, world."); 2858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// invokeExact(Ljava/io/PrintStream;Ljava/lang/String;)V 2868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 2878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Each of the above calls to {@code invokeExact} or plain {@code invoke} 2888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * generates a single invokevirtual instruction with 2898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the symbolic type descriptor indicated in the following comment. 2908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In these examples, the helper method {@code assertEquals} is assumed to 2918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * be a method which calls {@link java.util.Objects#equals(Object,Object) Objects.equals} 2928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * on its arguments, and asserts that the result is true. 2938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 2948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Exceptions</h1> 2958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The methods {@code invokeExact} and {@code invoke} are declared 2968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to throw {@link java.lang.Throwable Throwable}, 2978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which is to say that there is no static restriction on what a method handle 2988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * can throw. Since the JVM does not distinguish between checked 2998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and unchecked exceptions (other than by their class, of course), 3008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * there is no particular effect on bytecode shape from ascribing 3018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * checked exceptions to method handle invocations. But in Java source 3028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * code, methods which perform method handle calls must either explicitly 3038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * throw {@code Throwable}, or else must catch all 3048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * throwables locally, rethrowing only those which are legal in the context, 3058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and wrapping ones which are illegal. 3068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 3078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1><a name="sigpoly"></a>Signature polymorphism</h1> 3088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The unusual compilation and linkage behavior of 3098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code invokeExact} and plain {@code invoke} 3108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * is referenced by the term <em>signature polymorphism</em>. 3118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As defined in the Java Language Specification, 3128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a signature polymorphic method is one which can operate with 3138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * any of a wide range of call signatures and return types. 3148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In source code, a call to a signature polymorphic method will 3168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * compile, regardless of the requested symbolic type descriptor. 3178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As usual, the Java compiler emits an {@code invokevirtual} 3188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * instruction with the given symbolic type descriptor against the named method. 3198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The unusual part is that the symbolic type descriptor is derived from 3208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the actual argument and return types, not from the method declaration. 3218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When the JVM processes bytecode containing signature polymorphic calls, 3238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * it will successfully link any such call, regardless of its symbolic type descriptor. 3248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (In order to retain type safety, the JVM will guard such calls with suitable 3258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * dynamic type checks, as described elsewhere.) 3268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Bytecode generators, including the compiler back end, are required to emit 3288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * untransformed symbolic type descriptors for these methods. 3298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Tools which determine symbolic linkage are required to accept such 3308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * untransformed descriptors, without reporting linkage errors. 3318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 3328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Interoperation between method handles and the Core Reflection API</h1> 3336774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * Using factory methods in the {@link java.lang.invoke.MethodHandles.Lookup Lookup} API, 3348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * any class member represented by a Core Reflection API object 3358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * can be converted to a behaviorally equivalent method handle. 3368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * For example, a reflective {@link java.lang.reflect.Method Method} can 3378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * be converted to a method handle using 3386774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}. 3398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The resulting method handles generally provide more direct and efficient 3408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * access to the underlying class members. 3418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As a special case, 3438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * when the Core Reflection API is used to view the signature polymorphic 3448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * methods {@code invokeExact} or plain {@code invoke} in this class, 3458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * they appear as ordinary non-polymorphic methods. 3468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Their reflective appearance, as viewed by 3478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@link java.lang.Class#getDeclaredMethod Class.getDeclaredMethod}, 3488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * is unaffected by their special status in this API. 3498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * For example, {@link java.lang.reflect.Method#getModifiers Method.getModifiers} 3508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * will report exactly those modifier bits required for any similarly 3518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * declared method, including in this case {@code native} and {@code varargs} bits. 3528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As with any reflected method, these methods (when reflected) may be 3548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * invoked via {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}. 3558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * However, such reflective calls do not result in method handle invocations. 3568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Such a call, if passed the required argument 3578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (a single one, of type {@code Object[]}), will ignore the argument and 3588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * will throw an {@code UnsupportedOperationException}. 3598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Since {@code invokevirtual} instructions can natively 3618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * invoke method handles under any symbolic type descriptor, this reflective view conflicts 3628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * with the normal presentation of these methods via bytecodes. 3638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Thus, these two native methods, when reflectively viewed by 3648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code Class.getDeclaredMethod}, may be regarded as placeholders only. 3658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In order to obtain an invoker method for a particular type descriptor, 3676774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * use {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker}, 3686774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * or {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}. 3696774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * The {@link java.lang.invoke.MethodHandles.Lookup#findVirtual Lookup.findVirtual} 3708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * API is also able to return a method handle 3718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to call {@code invokeExact} or plain {@code invoke}, 3728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * for any specified type descriptor . 3738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 3748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1>Interoperation between method handles and Java generics</h1> 3758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * A method handle can be obtained on a method, constructor, or field 3768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which is declared with Java generic types. 3778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As with the Core Reflection API, the type of the method handle 3788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * will constructed from the erasure of the source-level type. 3798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When a method handle is invoked, the types of its arguments 3808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or the return value cast type may be generic types or type instances. 3818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If this occurs, the compiler will replace those 3828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * types by their erasures when it constructs the symbolic type descriptor 3838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * for the {@code invokevirtual} instruction. 3848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 3858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Method handles do not represent 3868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * their function-like types in terms of Java parameterized (generic) types, 3878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * because there are three mismatches between function-like types and parameterized 3888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Java types. 3898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <ul> 3908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Method types range over all possible arities, 3918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * from no arguments to up to the <a href="MethodHandle.html#maxarity">maximum number</a> of allowed arguments. 3928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Generics are not variadic, and so cannot represent this.</li> 3938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Method types can specify arguments of primitive types, 3948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which Java generic types cannot range over.</li> 3958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Higher order functions over method handles (combinators) are 3968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * often generic across a wide range of function types, including 3978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * those of multiple arities. It is impossible to represent such 3988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * genericity with a Java type parameter.</li> 3998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * </ul> 4008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 4018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <h1><a name="maxarity"></a>Arity limits</h1> 4028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The JVM imposes on all methods and constructors of any kind an absolute 4038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * limit of 255 stacked arguments. This limit can appear more restrictive 4048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * in certain cases: 4058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <ul> 4068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>A {@code long} or {@code double} argument counts (for purposes of arity limits) as two argument slots. 4078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>A non-static method consumes an extra argument for the object on which the method is called. 4088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>A constructor consumes an extra argument for the object which is being constructed. 4098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Since a method handle’s {@code invoke} method (or other signature-polymorphic method) is non-virtual, 4108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * it consumes an extra argument for the method handle itself, in addition to any non-virtual receiver object. 4118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * </ul> 4128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * These limits imply that certain method handles cannot be created, solely because of the JVM limit on stacked arguments. 4138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * For example, if a static JVM method accepts exactly 255 arguments, a method handle cannot be created for it. 4148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Attempts to create method handles with impossible method types lead to an {@link IllegalArgumentException}. 4158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In particular, a method handle’s type must not have an arity of the exact maximum 255. 4168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 4178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see MethodType 4186774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * @see MethodHandles 4198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @author John Rose, JSR 292 EG 4208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 4218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathpublic abstract class MethodHandle { 4228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Android-changed: 4238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 4248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // static { MethodHandleImpl.initStatics(); } 4258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 4268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // LambdaForm and customizationCount are currently unused in our implementation 4278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // and will be substituted with appropriate implementation / delegate classes. 4288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 4298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*private*/ final LambdaForm form; 4308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // form is not private so that invokers can easily fetch it 4318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ byte customizationCount; 4328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // customizationCount should be accessible from invokers 4338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 4348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 4358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 4368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Internal marker interface which distinguishes (to the Java compiler) 4378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * those methods which are <a href="MethodHandle.html#sigpoly">signature polymorphic</a>. 438cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath * 439cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath * @hide 4408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 4418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath @java.lang.annotation.Target({java.lang.annotation.ElementType.METHOD}) 4428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.RUNTIME) 443cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath public @interface PolymorphicSignature { } 4448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 445ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath /** 446ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath * The type of this method handle, this corresponds to the exact type of the method 447ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath * being invoked. 448ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath */ 4498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath private final MethodType type; 450ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath 451ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath /** 452ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath * The nominal type of this method handle, will be non-null if a method handle declares 453ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath * a different type from its "real" type, which is either the type of the method being invoked 454ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath * or the type of the emulated stackframe expected by an underyling adapter. 455ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath */ 456ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath private MethodType nominalType; 457ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath 45854168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath /** 45986dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath * The spread invoker associated with this type with zero trailing arguments. 46086dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath * This is used to speed up invokeWithArguments. 46186dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath */ 46286dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath private MethodHandle cachedSpreadInvoker; 46386dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath 46486dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath /** 46554168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath * The INVOKE* constants and SGET/SPUT and IGET/IPUT constants specify the behaviour of this 46654168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath * method handle with respect to the ArtField* or the ArtMethod* that it operates on. These 46754168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath * behaviours are equivalent to the dex bytecode behaviour on the respective method_id or 46854168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath * field_id in the equivalent instruction. 469faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * 470faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * INVOKE_TRANSFORM is a special type of handle which doesn't encode any dex bytecode behaviour, 471faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * instead it transforms the list of input arguments or performs other higher order operations 472faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * before (optionally) delegating to another method handle. 473704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson * 474704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson * INVOKE_CALLSITE_TRANSFORM is a variation on INVOKE_TRANSFORM where the method type of 475704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson * a MethodHandle dynamically varies based on the callsite. This is used by 476704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson * the VarargsCollector implementation which places any number of trailing arguments 477704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson * into an array before invoking an arity method. The "any number of trailing arguments" means 478704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson * it would otherwise generate WrongMethodTypeExceptions as the callsite method type and 479704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson * VarargsCollector method type appear incompatible. 48054168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath */ 48154168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath 4825bf2e16e7e789d8668c83851a1486e7bb1a286ffNarayan Kamath /** @hide */ public static final int INVOKE_VIRTUAL = 0; 4835bf2e16e7e789d8668c83851a1486e7bb1a286ffNarayan Kamath /** @hide */ public static final int INVOKE_SUPER = 1; 4845bf2e16e7e789d8668c83851a1486e7bb1a286ffNarayan Kamath /** @hide */ public static final int INVOKE_DIRECT = 2; 4855bf2e16e7e789d8668c83851a1486e7bb1a286ffNarayan Kamath /** @hide */ public static final int INVOKE_STATIC = 3; 4865bf2e16e7e789d8668c83851a1486e7bb1a286ffNarayan Kamath /** @hide */ public static final int INVOKE_INTERFACE = 4; 487faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath /** @hide */ public static final int INVOKE_TRANSFORM = 5; 488704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson /** @hide */ public static final int INVOKE_CALLSITE_TRANSFORM = 6; 48951e2e77cb38173a1598a7f014d5a0232da4818a8Orion Hodson /** @hide */ public static final int INVOKE_VAR_HANDLE = 7; 49051e2e77cb38173a1598a7f014d5a0232da4818a8Orion Hodson /** @hide */ public static final int INVOKE_VAR_HANDLE_EXACT = 8; 49151e2e77cb38173a1598a7f014d5a0232da4818a8Orion Hodson /** @hide */ public static final int IGET = 9; 49251e2e77cb38173a1598a7f014d5a0232da4818a8Orion Hodson /** @hide */ public static final int IPUT = 10; 49351e2e77cb38173a1598a7f014d5a0232da4818a8Orion Hodson /** @hide */ public static final int SGET = 11; 49451e2e77cb38173a1598a7f014d5a0232da4818a8Orion Hodson /** @hide */ public static final int SPUT = 12; 49554168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath 49654168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath // The kind of this method handle (used by the runtime). This is one of the INVOKE_* 49754168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath // constants or SGET/SPUT, IGET/IPUT. 498cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath /** @hide */ protected final int handleKind; 49954168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath 500ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath // The ArtMethod* or ArtField* associated with this method handle (used by the runtime). 501cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath /** @hide */ protected final long artFieldOrMethod; 502ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath 503cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath /** @hide */ 504ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath protected MethodHandle(long artFieldOrMethod, int handleKind, MethodType type) { 505ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath this.artFieldOrMethod = artFieldOrMethod; 506ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath this.handleKind = handleKind; 507ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath this.type = type; 508ed438115cf887c4541cb292244b8234c0aa19b1cNarayan Kamath } 5098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 5108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 5118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Reports the type of this method handle. 5128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Every invocation of this method handle via {@code invokeExact} must exactly match this type. 5138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return the method handle type 5148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 5158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public MethodType type() { 516ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath if (nominalType != null) { 517ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath return nominalType; 518ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath } 519ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath 5208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath return type; 5218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 5228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 5238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 5248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Invokes the method handle, allowing any caller type descriptor, but requiring an exact type match. 5258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The symbolic type descriptor at the call site of {@code invokeExact} must 5268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * exactly match this method handle's {@link #type type}. 5278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * No conversions are allowed on arguments or return values. 5288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 5298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When this method is observed via the Core Reflection API, 5308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * it will appear as a single native method, taking an object array and returning an object. 5318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If this native method is invoked directly via 5328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI, 5336774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}, 5348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * it will throw an {@code UnsupportedOperationException}. 5358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param args the signature-polymorphic parameter list, statically represented using varargs 5368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return the signature-polymorphic result, statically represented using {@code Object} 5378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws WrongMethodTypeException if the target's type is not identical with the caller's symbolic type descriptor 5388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call 5398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 5408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public final native @PolymorphicSignature Object invokeExact(Object... args) throws Throwable; 5418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 5428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 5438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Invokes the method handle, allowing any caller type descriptor, 5448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and optionally performing conversions on arguments and return values. 5458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 5468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the call site's symbolic type descriptor exactly matches this method handle's {@link #type type}, 5478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the call proceeds as if by {@link #invokeExact invokeExact}. 5488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 5498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Otherwise, the call proceeds as if this method handle were first 5508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * adjusted by calling {@link #asType asType} to adjust this method handle 5518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the required type, and then the call proceeds as if by 5528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@link #invokeExact invokeExact} on the adjusted method handle. 5538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 5548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * There is no guarantee that the {@code asType} call is actually made. 5558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the JVM can predict the results of making the call, it may perform 5568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * adaptations directly on the caller's arguments, 5578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and call the target method handle according to its own exact type. 5588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 5598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The resolved type descriptor at the call site of {@code invoke} must 5608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * be a valid argument to the receivers {@code asType} method. 5618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In particular, the caller must specify the same argument arity 5628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as the callee's type, 5638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * if the callee is not a {@linkplain #asVarargsCollector variable arity collector}. 5648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 5658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When this method is observed via the Core Reflection API, 5668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * it will appear as a single native method, taking an object array and returning an object. 5678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If this native method is invoked directly via 5688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI, 5696774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}, 5708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * it will throw an {@code UnsupportedOperationException}. 5718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param args the signature-polymorphic parameter list, statically represented using varargs 5728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return the signature-polymorphic result, statically represented using {@code Object} 5738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws WrongMethodTypeException if the target's type cannot be adjusted to the caller's symbolic type descriptor 5748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws ClassCastException if the target's type can be adjusted to the caller, but a reference cast fails 5758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call 5768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 5778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public final native @PolymorphicSignature Object invoke(Object... args) throws Throwable; 5788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 5798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Android-changed: Removed implementation details. 5808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 5818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ final native @PolymorphicSignature Object invokeBasic(Object... args) 5828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ static native @PolymorphicSignature Object linkToVirtual(Object... args) 5838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ static native @PolymorphicSignature Object linkToStatic(Object... args) 5848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ static native @PolymorphicSignature Object linkToSpecial(Object... args) 5858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ static native @PolymorphicSignature Object linkToInterface(Object... args) 5868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 5878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 5888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Performs a variable arity invocation, passing the arguments in the given list 5898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the method handle, as if via an inexact {@link #invoke invoke} from a call site 5908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which mentions only the type {@code Object}, and whose arity is the length 5918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of the argument list. 5928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 5938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Specifically, execution proceeds as if by the following steps, 5948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * although the methods are not guaranteed to be called if the JVM 5958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * can predict their effects. 5968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <ul> 5978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Determine the length of the argument array as {@code N}. 5988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * For a null reference, {@code N=0}. </li> 5998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Determine the general type {@code TN} of {@code N} arguments as 6008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as {@code TN=MethodType.genericMethodType(N)}.</li> 6018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Force the original target method handle {@code MH0} to the 6028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * required type, as {@code MH1 = MH0.asType(TN)}. </li> 6038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Spread the array into {@code N} separate arguments {@code A0, ...}. </li> 6048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Invoke the type-adjusted method handle on the unpacked arguments: 6058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * MH1.invokeExact(A0, ...). </li> 6068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Take the return value as an {@code Object} reference. </li> 6078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * </ul> 6088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Because of the action of the {@code asType} step, the following argument 6108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * conversions are applied as necessary: 6118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <ul> 6128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>reference casting 6138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>unboxing 6148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>widening primitive conversions 6158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * </ul> 6168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The result returned by the call is boxed if it is a primitive, 6188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or forced to null if the return type is void. 6198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This call is equivalent to the following code: 6218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 6228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * MethodHandle invoker = MethodHandles.spreadInvoker(this.type(), 0); 6238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Object result = invoker.invokeExact(this, arguments); 6248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 6258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Unlike the signature polymorphic methods {@code invokeExact} and {@code invoke}, 6278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code invokeWithArguments} can be accessed normally via the Core Reflection API and JNI. 6288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * It can therefore be used as a bridge between native or reflective code and method handles. 6298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 6308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param arguments the arguments to pass to the target 6318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return the result returned by the target 6328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws ClassCastException if an argument cannot be converted by reference casting 6338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments 6348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws Throwable anything thrown by the target method invocation 6356774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * @see MethodHandles#spreadInvoker 6368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 6378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public Object invokeWithArguments(Object... arguments) throws Throwable { 63886dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath MethodHandle invoker = null; 63986dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath synchronized (this) { 64086dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath if (cachedSpreadInvoker == null) { 64186dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath cachedSpreadInvoker = MethodHandles.spreadInvoker(this.type(), 0); 64286dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath } 64386dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath 64486dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath invoker = cachedSpreadInvoker; 64586dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath } 64686dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath 64786dc78f165d24514cb094db95e8bad99618626e9Narayan Kamath return invoker.invoke(this, arguments); 6488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 6498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 6508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 6518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Performs a variable arity invocation, passing the arguments in the given array 6528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the method handle, as if via an inexact {@link #invoke invoke} from a call site 6538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which mentions only the type {@code Object}, and whose arity is the length 6548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of the argument array. 6558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This method is also equivalent to the following code: 6578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 6588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * invokeWithArguments(arguments.toArray() 6598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 6608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 6618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param arguments the arguments to pass to the target 6628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return the result returned by the target 6638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws NullPointerException if {@code arguments} is a null reference 6648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws ClassCastException if an argument cannot be converted by reference casting 6658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments 6668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws Throwable anything thrown by the target method invocation 6678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 6688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public Object invokeWithArguments(java.util.List<?> arguments) throws Throwable { 6698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath return invokeWithArguments(arguments.toArray()); 6708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 6718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 6728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 6738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Produces an adapter method handle which adapts the type of the 6748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * current method handle to a new type. 6758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The resulting method handle is guaranteed to report a type 6768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which is equal to the desired new type. 6778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the original type and new type are equal, returns {@code this}. 6798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The new method handle, when invoked, will perform the following 6818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * steps: 6828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <ul> 6838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Convert the incoming argument list to match the original 6848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * method handle's argument list. 6858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Invoke the original method handle on the converted argument list. 6868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>Convert any result returned by the original method handle 6878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the return type of new method handle. 6888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * </ul> 6898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This method provides the crucial behavioral difference between 6918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@link #invokeExact invokeExact} and plain, inexact {@link #invoke invoke}. 6928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The two methods 6938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * perform the same steps when the caller's type descriptor exactly m atches 6948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the callee's, but when the types differ, plain {@link #invoke invoke} 6958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * also calls {@code asType} (or some internal equivalent) in order 6968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to match up the caller's and callee's types. 6978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 6988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the current method is a variable arity method handle 6998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * argument list conversion may involve the conversion and collection 7008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of several arguments into an array, as 7018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@linkplain #asVarargsCollector described elsewhere}. 7028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In every other case, all conversions are applied <em>pairwise</em>, 7038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which means that each argument or return value is converted to 7048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * exactly one argument or return value (or no return value). 7058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The applied conversions are defined by consulting the 7068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the corresponding component types of the old and new 7078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * method handle types. 7088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 7098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Let <em>T0</em> and <em>T1</em> be corresponding new and old parameter types, 7108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or old and new return types. Specifically, for some valid index {@code i}, let 7118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <em>T0</em>{@code =newType.parameterType(i)} and <em>T1</em>{@code =this.type().parameterType(i)}. 7128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Or else, going the other way for return values, let 7138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <em>T0</em>{@code =this.type().returnType()} and <em>T1</em>{@code =newType.returnType()}. 7148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the types are the same, the new method handle makes no change 7158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the corresponding argument or return value (if any). 7168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Otherwise, one of the following conversions is applied 7178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * if possible: 7188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <ul> 7198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>If <em>T0</em> and <em>T1</em> are references, then a cast to <em>T1</em> is applied. 7208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (The types do not need to be related in any particular way. 7218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This is because a dynamic value of null can convert to any reference type.) 7228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>If <em>T0</em> and <em>T1</em> are primitives, then a Java method invocation 7238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * conversion (JLS 5.3) is applied, if one exists. 7248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (Specifically, <em>T0</em> must convert to <em>T1</em> by a widening primitive conversion.) 7258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>If <em>T0</em> is a primitive and <em>T1</em> a reference, 7268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a Java casting conversion (JLS 5.5) is applied if one exists. 7278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (Specifically, the value is boxed from <em>T0</em> to its wrapper class, 7288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which is then widened as needed to <em>T1</em>.) 7298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing 7308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * conversion will be applied at runtime, possibly followed 7318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * by a Java method invocation conversion (JLS 5.3) 7328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * on the primitive value. (These are the primitive widening conversions.) 7338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <em>T0</em> must be a wrapper class or a supertype of one. 7348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (In the case where <em>T0</em> is Object, these are the conversions 7358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * allowed by {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}.) 7368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The unboxing conversion must have a possibility of success, which means that 7378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * if <em>T0</em> is not itself a wrapper class, there must exist at least one 7388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * wrapper class <em>TW</em> which is a subtype of <em>T0</em> and whose unboxed 7398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * primitive value can be widened to <em>T1</em>. 7408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>If the return type <em>T1</em> is marked as void, any returned value is discarded 7418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>If the return type <em>T0</em> is void and <em>T1</em> a reference, a null value is introduced. 7428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>If the return type <em>T0</em> is void and <em>T1</em> a primitive, 7438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a zero value is introduced. 7448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * </ul> 7458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (<em>Note:</em> Both <em>T0</em> and <em>T1</em> may be regarded as static types, 7468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * because neither corresponds specifically to the <em>dynamic type</em> of any 7478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * actual argument or return value.) 7488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 7498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The method handle conversion cannot be made if any one of the required 7508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * pairwise conversions cannot be made. 7518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 7528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * At runtime, the conversions applied to reference arguments 7538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or return values may require additional runtime checks which can fail. 7548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * An unboxing operation may fail because the original reference is null, 7558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * causing a {@link java.lang.NullPointerException NullPointerException}. 7568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * An unboxing operation or a reference cast may also fail on a reference 7578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to an object of the wrong type, 7588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * causing a {@link java.lang.ClassCastException ClassCastException}. 7598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Although an unboxing operation may accept several kinds of wrappers, 7608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * if none are available, a {@code ClassCastException} will be thrown. 7618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 7628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param newType the expected type of the new method handle 7638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return a method handle which delegates to {@code this} after performing 7648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * any necessary argument conversions, and arranges for any 7658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * necessary return value conversions 7668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws NullPointerException if {@code newType} is a null reference 7678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws WrongMethodTypeException if the conversion cannot be made 7686774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * @see MethodHandles#explicitCastArguments 7698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 7708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public MethodHandle asType(MethodType newType) { 7718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Fast path alternative to a heavyweight {@code asType} call. 7728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Return 'this' if the conversion will be a no-op. 7738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (newType == type) { 7748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath return this; 7758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 7768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 777ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath if (!type.isConvertibleTo(newType)) { 778ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath throw new WrongMethodTypeException("cannot convert " + this + " to " + newType); 7798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 7808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 781ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath MethodHandle mh = duplicate(); 782ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath mh.nominalType = newType; 783ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath return mh; 7848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 7858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 7868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 7878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Makes an <em>array-spreading</em> method handle, which accepts a trailing array argument 7888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and spreads its elements as positional arguments. 7898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The new method handle adapts, as its <i>target</i>, 7908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the current method handle. The type of the adapter will be 7918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the same as the type of the target, except that the final 7928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code arrayLength} parameters of the target's type are replaced 7938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * by a single array parameter of type {@code arrayType}. 7948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 7958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the array element type differs from any of the corresponding 7968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * argument types on the original target, 7978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the original target is adapted to take the array elements directly, 7988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as if by a call to {@link #asType asType}. 7998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 8008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When called, the adapter replaces a trailing array argument 8018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * by the array's elements, each as its own argument to the target. 8028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (The order of the arguments is preserved.) 8038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * They are converted pairwise by casting and/or unboxing 8048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the types of the trailing parameters of the target. 8058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Finally the target is called. 8068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * What the target eventually returns is returned unchanged by the adapter. 8078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 8088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Before calling the target, the adapter verifies that the array 8098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * contains exactly enough elements to provide a correct argument count 8108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the target method handle. 8118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (The array may also be null when zero elements are required.) 8128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 8138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If, when the adapter is called, the supplied array argument does 8148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * not have the correct number of elements, the adapter will throw 8158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * an {@link IllegalArgumentException} instead of invoking the target. 8168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 8178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Here are some simple examples of array-spreading method handles: 8188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 8198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle equals = publicLookup() 8208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findVirtual(String.class, "equals", methodType(boolean.class, Object.class)); 8218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert( (boolean) equals.invokeExact("me", (Object)"me")); 8228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(!(boolean) equals.invokeExact("me", (Object)"thee")); 8238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// spread both arguments from a 2-array: 8248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle eq2 = equals.asSpreader(Object[].class, 2); 8258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert( (boolean) eq2.invokeExact(new Object[]{ "me", "me" })); 8268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(!(boolean) eq2.invokeExact(new Object[]{ "me", "thee" })); 8278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// try to spread from anything but a 2-array: 8288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathfor (int n = 0; n <= 10; n++) { 8298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath Object[] badArityArgs = (n == 2 ? null : new Object[n]); 8308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath try { assert((boolean) eq2.invokeExact(badArityArgs) && false); } 8318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath catch (IllegalArgumentException ex) { } // OK 8328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath} 8338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// spread both arguments from a String array: 8348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle eq2s = equals.asSpreader(String[].class, 2); 8358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert( (boolean) eq2s.invokeExact(new String[]{ "me", "me" })); 8368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(!(boolean) eq2s.invokeExact(new String[]{ "me", "thee" })); 8378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// spread second arguments from a 1-array: 8388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle eq1 = equals.asSpreader(Object[].class, 1); 8398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert( (boolean) eq1.invokeExact("me", new Object[]{ "me" })); 8408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(!(boolean) eq1.invokeExact("me", new Object[]{ "thee" })); 8418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// spread no arguments from a 0-array or null: 8428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle eq0 = equals.asSpreader(Object[].class, 0); 8438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert( (boolean) eq0.invokeExact("me", (Object)"me", new Object[0])); 8448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(!(boolean) eq0.invokeExact("me", (Object)"thee", (Object[])null)); 8458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// asSpreader and asCollector are approximate inverses: 8468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathfor (int n = 0; n <= 2; n++) { 8478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath for (Class<?> a : new Class<?>[]{Object[].class, String[].class, CharSequence[].class}) { 8488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath MethodHandle equals2 = equals.asSpreader(a, n).asCollector(a, n); 8498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath assert( (boolean) equals2.invokeWithArguments("me", "me")); 8508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath assert(!(boolean) equals2.invokeWithArguments("me", "thee")); 8518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 8528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath} 8538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle caToString = publicLookup() 8548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findStatic(Arrays.class, "toString", methodType(String.class, char[].class)); 8558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[A, B, C]", (String) caToString.invokeExact("ABC".toCharArray())); 8568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle caString3 = caToString.asCollector(char[].class, 3); 8578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[A, B, C]", (String) caString3.invokeExact('A', 'B', 'C')); 8588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle caToString2 = caString3.asSpreader(char[].class, 2); 8598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[A, B, C]", (String) caToString2.invokeExact('A', "BC".toCharArray())); 8608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 8618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param arrayType usually {@code Object[]}, the type of the array argument from which to extract the spread arguments 8628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param arrayLength the number of arguments to spread from an incoming array argument 8638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return a new method handle which spreads its final array argument, 8648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * before calling the original method handle 8658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws NullPointerException if {@code arrayType} is a null reference 8668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws IllegalArgumentException if {@code arrayType} is not an array type, 8678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or if target does not have at least 8688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code arrayLength} parameter types, 8698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or if {@code arrayLength} is negative, 8708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or if the resulting method handle's type would have 8718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <a href="MethodHandle.html#maxarity">too many parameters</a> 8728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws WrongMethodTypeException if the implied {@code asType} call fails 8738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asCollector 8748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 8758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public MethodHandle asSpreader(Class<?> arrayType, int arrayLength) { 8768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath MethodType postSpreadType = asSpreaderChecks(arrayType, arrayLength); 8778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 878378d458718d98d264b58734c87568ee5de9a6781Narayan Kamath final int targetParamCount = postSpreadType.parameterCount(); 879378d458718d98d264b58734c87568ee5de9a6781Narayan Kamath MethodType dropArrayArgs = postSpreadType.dropParameterTypes( 880378d458718d98d264b58734c87568ee5de9a6781Narayan Kamath (targetParamCount - arrayLength), targetParamCount); 881378d458718d98d264b58734c87568ee5de9a6781Narayan Kamath MethodType adapterType = dropArrayArgs.appendParameterTypes(arrayType); 882378d458718d98d264b58734c87568ee5de9a6781Narayan Kamath 883378d458718d98d264b58734c87568ee5de9a6781Narayan Kamath return new Transformers.Spreader(this, adapterType, arrayLength); 8848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 8858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 8868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 8878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * See if {@code asSpreader} can be validly called with the given arguments. 8888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Return the type of the method handle call after spreading but before conversions. 8898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 8908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath private MethodType asSpreaderChecks(Class<?> arrayType, int arrayLength) { 8918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath spreadArrayChecks(arrayType, arrayLength); 8928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath int nargs = type().parameterCount(); 8938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (nargs < arrayLength || arrayLength < 0) 8948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath throw newIllegalArgumentException("bad spread array length"); 8958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath Class<?> arrayElement = arrayType.getComponentType(); 8968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath MethodType mtype = type(); 8978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath boolean match = true, fail = false; 8988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath for (int i = nargs - arrayLength; i < nargs; i++) { 8998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath Class<?> ptype = mtype.parameterType(i); 9008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (ptype != arrayElement) { 9018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath match = false; 9028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (!MethodType.canConvert(arrayElement, ptype)) { 9038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath fail = true; 9048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath break; 9058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 9068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 9078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 9088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (match) return mtype; 9098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath MethodType needType = mtype.asSpreaderType(arrayType, arrayLength); 9108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (!fail) return needType; 9118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // elicit an error: 9128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath this.asType(needType); 9138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath throw newInternalError("should not return", null); 9148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 9158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 9168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath private void spreadArrayChecks(Class<?> arrayType, int arrayLength) { 9178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath Class<?> arrayElement = arrayType.getComponentType(); 9188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (arrayElement == null) 9198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath throw newIllegalArgumentException("not an array type", arrayType); 9208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if ((arrayLength & 0x7F) != arrayLength) { 9218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if ((arrayLength & 0xFF) != arrayLength) 9228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath throw newIllegalArgumentException("array length is not legal", arrayLength); 9238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath assert(arrayLength >= 128); 9248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (arrayElement == long.class || 9258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath arrayElement == double.class) 9268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath throw newIllegalArgumentException("array length is not legal for long[] or double[]", arrayLength); 9278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 9288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 9298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 9308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 9318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Makes an <em>array-collecting</em> method handle, which accepts a given number of trailing 9328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * positional arguments and collects them into an array argument. 9338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The new method handle adapts, as its <i>target</i>, 9348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the current method handle. The type of the adapter will be 9358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the same as the type of the target, except that a single trailing 9368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * parameter (usually of type {@code arrayType}) is replaced by 9378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code arrayLength} parameters whose type is element type of {@code arrayType}. 9388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 9398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the array type differs from the final argument type on the original target, 9408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the original target is adapted to take the array type directly, 9418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as if by a call to {@link #asType asType}. 9428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 9438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When called, the adapter replaces its trailing {@code arrayLength} 9448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * arguments by a single new array of type {@code arrayType}, whose elements 9458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * comprise (in order) the replaced arguments. 9468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Finally the target is called. 9478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * What the target eventually returns is returned unchanged by the adapter. 9488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 9498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (The array may also be a shared constant when {@code arrayLength} is zero.) 9508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 9518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (<em>Note:</em> The {@code arrayType} is often identical to the last 9528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * parameter type of the original target. 9538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * It is an explicit argument for symmetry with {@code asSpreader}, and also 9548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to allow the target to use a simple {@code Object} as its last parameter type.) 9558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 9568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In order to create a collecting adapter which is not restricted to a particular 9578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * number of collected arguments, use {@link #asVarargsCollector asVarargsCollector} instead. 9588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 9598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Here are some examples of array-collecting method handles: 9608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 9618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle deepToString = publicLookup() 9628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 9638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[won]", (String) deepToString.invokeExact(new Object[]{"won"})); 9648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle ts1 = deepToString.asCollector(Object[].class, 1); 9658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(methodType(String.class, Object.class), ts1.type()); 9668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath//assertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"})); //FAIL 9678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[[won]]", (String) ts1.invokeExact((Object) new Object[]{"won"})); 9688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// arrayType can be a subtype of Object[] 9698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle ts2 = deepToString.asCollector(String[].class, 2); 9708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(methodType(String.class, String.class, String.class), ts2.type()); 9718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[two, too]", (String) ts2.invokeExact("two", "too")); 9728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle ts0 = deepToString.asCollector(Object[].class, 0); 9738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[]", (String) ts0.invokeExact()); 9748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// collectors can be nested, Lisp-style 9758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle ts22 = deepToString.asCollector(Object[].class, 3).asCollector(String[].class, 2); 9768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[A, B, [C, D]]", ((String) ts22.invokeExact((Object)'A', (Object)"B", "C", "D"))); 9778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// arrayType can be any primitive array type 9788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle bytesToString = publicLookup() 9798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findStatic(Arrays.class, "toString", methodType(String.class, byte[].class)) 9808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .asCollector(byte[].class, 3); 9818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[1, 2, 3]", (String) bytesToString.invokeExact((byte)1, (byte)2, (byte)3)); 9828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle longsToString = publicLookup() 9838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findStatic(Arrays.class, "toString", methodType(String.class, long[].class)) 9848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .asCollector(long[].class, 1); 9858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[123]", (String) longsToString.invokeExact((long)123)); 9868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 9878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments 9888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param arrayLength the number of arguments to collect into a new array argument 9898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return a new method handle which collects some trailing argument 9908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * into an array, before calling the original method handle 9918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws NullPointerException if {@code arrayType} is a null reference 9928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws IllegalArgumentException if {@code arrayType} is not an array type 9938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or {@code arrayType} is not assignable to this method handle's trailing parameter type, 9948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or {@code arrayLength} is not a legal array size, 9958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or the resulting method handle's type would have 9968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <a href="MethodHandle.html#maxarity">too many parameters</a> 9978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws WrongMethodTypeException if the implied {@code asType} call fails 9988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asSpreader 9998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asVarargsCollector 10008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 10018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public MethodHandle asCollector(Class<?> arrayType, int arrayLength) { 10028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath asCollectorChecks(arrayType, arrayLength); 10038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 10040e8de7372de378e00c429dbf9d55526d433a7a21Narayan Kamath return new Transformers.Collector(this, arrayType, arrayLength); 10058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 10068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 10078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 10088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * See if {@code asCollector} can be validly called with the given arguments. 10098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Return false if the last parameter is not an exact match to arrayType. 10108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 10118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /*non-public*/ boolean asCollectorChecks(Class<?> arrayType, int arrayLength) { 10128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath spreadArrayChecks(arrayType, arrayLength); 10138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath int nargs = type().parameterCount(); 10148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (nargs != 0) { 10158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath Class<?> lastParam = type().parameterType(nargs-1); 10168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (lastParam == arrayType) return true; 10178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (lastParam.isAssignableFrom(arrayType)) return false; 10188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 10198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath throw newIllegalArgumentException("array type not assignable to trailing argument", this, arrayType); 10208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 10218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 10228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 10238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Makes a <em>variable arity</em> adapter which is able to accept 10248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * any number of trailing positional arguments and collect them 10258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * into an array argument. 10268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The type and behavior of the adapter will be the same as 10288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the type and behavior of the target, except that certain 10298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code invoke} and {@code asType} requests can lead to 10308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * trailing positional arguments being collected into target's 10318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * trailing parameter. 10328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Also, the last parameter type of the adapter will be 10338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code arrayType}, even if the target has a different 10348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * last parameter type. 10358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This transformation may return {@code this} if the method handle is 10378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * already of variable arity and its trailing parameter type 10388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * is identical to {@code arrayType}. 10398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When called with {@link #invokeExact invokeExact}, the adapter invokes 10418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the target with no argument changes. 10428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (<em>Note:</em> This behavior is different from a 1043f4ee5c6dccff8f7e037f95b26767e552ea93d41bNarayan Kamath * {@linkplain #asCollector fixed arity collector}, 10448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * since it accepts a whole array of indeterminate length, 10458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * rather than a fixed number of arguments.) 10468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When called with plain, inexact {@link #invoke invoke}, if the caller 10488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * type is the same as the adapter, the adapter invokes the target as with 10498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code invokeExact}. 10508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (This is the normal behavior for {@code invoke} when types match.) 10518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Otherwise, if the caller and adapter arity are the same, and the 10538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * trailing parameter type of the caller is a reference type identical to 10548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or assignable to the trailing parameter type of the adapter, 10558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the arguments and return values are converted pairwise, 10568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as if by {@link #asType asType} on a fixed arity 10578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * method handle. 10588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Otherwise, the arities differ, or the adapter's trailing parameter 10608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * type is not assignable from the corresponding caller type. 10618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In this case, the adapter replaces all trailing arguments from 10628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the original trailing argument position onward, by 10638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a new array of type {@code arrayType}, whose elements 10648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * comprise (in order) the replaced arguments. 10658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The caller type must provides as least enough arguments, 10678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * and of the correct type, to satisfy the target's requirement for 10688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * positional arguments before the trailing array argument. 10698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Thus, the caller must supply, at a minimum, {@code N-1} arguments, 10708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * where {@code N} is the arity of the target. 10718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Also, there must exist conversions from the incoming arguments 10728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the target's arguments. 10738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * As with other uses of plain {@code invoke}, if these basic 10748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * requirements are not fulfilled, a {@code WrongMethodTypeException} 10758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * may be thrown. 10768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In all cases, what the target eventually returns is returned unchanged by the adapter. 10788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In the final case, it is exactly as if the target method handle were 1080f4ee5c6dccff8f7e037f95b26767e552ea93d41bNarayan Kamath * temporarily adapted with a {@linkplain #asCollector fixed arity collector} 10818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the arity required by the caller type. 10828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (As with {@code asCollector}, if the array length is zero, 10838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a shared constant may be used instead of a new array. 10848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the implied call to {@code asCollector} would throw 10858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * an {@code IllegalArgumentException} or {@code WrongMethodTypeException}, 10868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the call to the variable arity adapter must throw 10878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@code WrongMethodTypeException}.) 10888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 10898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The behavior of {@link #asType asType} is also specialized for 10908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * variable arity adapters, to maintain the invariant that 10918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * plain, inexact {@code invoke} is always equivalent to an {@code asType} 10928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * call to adjust the target type, followed by {@code invokeExact}. 10938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Therefore, a variable arity adapter responds 10948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to an {@code asType} request by building a fixed arity collector, 10958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * if and only if the adapter and requested type differ either 10968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * in arity or trailing argument type. 10978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The resulting fixed arity collector has its type further adjusted 10988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (if necessary) to the requested type by pairwise conversion, 10998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as if by another application of {@code asType}. 11008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 11018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When a method handle is obtained by executing an {@code ldc} instruction 11028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of a {@code CONSTANT_MethodHandle} constant, and the target method is marked 11038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as a variable arity method (with the modifier bit {@code 0x0080}), 11048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the method handle will accept multiple arities, as if the method handle 11058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * constant were created by means of a call to {@code asVarargsCollector}. 11068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 11078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In order to create a collecting adapter which collects a predetermined 11088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * number of arguments, and whose type reflects this predetermined number, 1109f4ee5c6dccff8f7e037f95b26767e552ea93d41bNarayan Kamath * use {@link #asCollector asCollector} instead. 11108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 11118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * No method handle transformations produce new method handles with 11128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * variable arity, unless they are documented as doing so. 11138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Therefore, besides {@code asVarargsCollector}, 11148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * all methods in {@code MethodHandle} and {@code MethodHandles} 11158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * will return a method handle with fixed arity, 11168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * except in the cases where they are specified to return their original 11178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * operand (e.g., {@code asType} of the method handle's own type). 11188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 11198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Calling {@code asVarargsCollector} on a method handle which is already 11208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of variable arity will produce a method handle with the same type and behavior. 11218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * It may (or may not) return the original variable arity method handle. 11228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 11238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Here is an example, of a list-making variable arity method handle: 11248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 11258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle deepToString = publicLookup() 11268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 11278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle ts1 = deepToString.asVarargsCollector(Object[].class); 11288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"})); 11298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[won]", (String) ts1.invoke( new Object[]{"won"})); 11308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[won]", (String) ts1.invoke( "won" )); 11318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[[won]]", (String) ts1.invoke((Object) new Object[]{"won"})); 11328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath// findStatic of Arrays.asList(...) produces a variable arity method handle: 11338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle asList = publicLookup() 11348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class)); 11358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(methodType(List.class, Object[].class), asList.type()); 11368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(asList.isVarargsCollector()); 11378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[]", asList.invoke().toString()); 11388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[1]", asList.invoke(1).toString()); 11398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[two, too]", asList.invoke("two", "too").toString()); 11408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathString[] argv = { "three", "thee", "tee" }; 11418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[three, thee, tee]", asList.invoke(argv).toString()); 11428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[three, thee, tee]", asList.invoke((Object[])argv).toString()); 11438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathList ls = (List) asList.invoke((Object)argv); 11448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(1, ls.size()); 11458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[three, thee, tee]", Arrays.toString((Object[])ls.get(0))); 11468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 11478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p style="font-size:smaller;"> 11488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <em>Discussion:</em> 11498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * These rules are designed as a dynamically-typed variation 11508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * of the Java rules for variable arity methods. 11518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In both cases, callers to a variable arity method or method handle 11528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * can either pass zero or more positional arguments, or else pass 11538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * pre-collected arrays of any length. Users should be aware of the 11548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * special role of the final argument, and of the effect of a 11558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * type match on that final argument, which determines whether 11568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or not a single trailing argument is interpreted as a whole 11578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * array or a single element of an array to be collected. 11588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Note that the dynamic type of the trailing argument has no 11598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * effect on this decision, only a comparison between the symbolic 11608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * type descriptor of the call site and the type descriptor of the method handle.) 11618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 11628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments 11638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return a new method handle which can collect any number of trailing arguments 11648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * into an array, before calling the original method handle 11658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws NullPointerException if {@code arrayType} is a null reference 11668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws IllegalArgumentException if {@code arrayType} is not an array type 11678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * or {@code arrayType} is not assignable to this method handle's trailing parameter type 11688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asCollector 11698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #isVarargsCollector 11708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asFixedArity 11718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 11728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public MethodHandle asVarargsCollector(Class<?> arrayType) { 11738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath arrayType.getClass(); // explicit NPE 11748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath boolean lastMatch = asCollectorChecks(arrayType, 0); 11758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath if (isVarargsCollector() && lastMatch) 11768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath return this; 11778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 1178704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson return new Transformers.VarargsCollector(this); 11798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 11808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 11818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 11828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Determines if this method handle 11838b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * supports {@linkplain #asVarargsCollector variable arity} calls. 11848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Such method handles arise from the following sources: 11858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <ul> 11868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>a call to {@linkplain #asVarargsCollector asVarargsCollector} 11876774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * <li>a call to a {@linkplain java.lang.invoke.MethodHandles.Lookup lookup method} 11888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which resolves to a variable arity Java method or constructor 11898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <li>an {@code ldc} instruction of a {@code CONSTANT_MethodHandle} 11908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * which resolves to a variable arity Java method or constructor 11918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * </ul> 11928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return true if this method handle accepts more than one arity of plain, inexact {@code invoke} calls 11938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asVarargsCollector 11948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asFixedArity 11958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 11968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public boolean isVarargsCollector() { 11978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath return false; 11988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 11998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 12008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 12018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Makes a <em>fixed arity</em> method handle which is otherwise 12028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * equivalent to the current method handle. 12038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 12048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * If the current method handle is not of 12058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * {@linkplain #asVarargsCollector variable arity}, 12068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the current method handle is returned. 12078b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * This is true even if the current method handle 12088b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * could not be a valid input to {@code asVarargsCollector}. 12098b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 12108b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Otherwise, the resulting fixed-arity method handle has the same 12118b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * type and behavior of the current method handle, 12128b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * except that {@link #isVarargsCollector isVarargsCollector} 12138b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * will be false. 12148b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The fixed-arity method handle may (or may not) be the 12158b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * a previous argument to {@code asVarargsCollector}. 12168b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 12178b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Here is an example, of a list-making variable arity method handle: 12188b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 12198b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle asListVar = publicLookup() 12208b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class)) 12218b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath .asVarargsCollector(Object[].class); 12228b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathMethodHandle asListFix = asListVar.asFixedArity(); 12238b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[1]", asListVar.invoke(1).toString()); 12248b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathException caught = null; 12258b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathtry { asListFix.invoke((Object)1); } 12268b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathcatch (Exception ex) { caught = ex; } 12278b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(caught instanceof ClassCastException); 12288b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[two, too]", asListVar.invoke("two", "too").toString()); 12298b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathtry { asListFix.invoke("two", "too"); } 12308b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathcatch (Exception ex) { caught = ex; } 12318b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamathassert(caught instanceof WrongMethodTypeException); 12328b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathObject[] argv = { "three", "thee", "tee" }; 12338b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[three, thee, tee]", asListVar.invoke(argv).toString()); 12348b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[three, thee, tee]", asListFix.invoke(argv).toString()); 12358b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals(1, ((List) asListVar.invoke((Object)argv)).size()); 12368b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan KamathassertEquals("[three, thee, tee]", asListFix.invoke((Object)argv).toString()); 12378b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 12388b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 12398b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return a new method handle which accepts only a fixed number of arguments 12408b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #asVarargsCollector 12418b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @see #isVarargsCollector 12428b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 12438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public MethodHandle asFixedArity() { 1244704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson // Android-changed: implementation specific. 1245704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson MethodHandle mh = this; 1246704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson if (mh.isVarargsCollector()) { 1247704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson mh = ((Transformers.VarargsCollector) mh).asFixedArity(); 1248704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson } 1249704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson assert(!mh.isVarargsCollector()); 1250704b13a41cc7efd49acf66064109756a248fe0dcOrion Hodson return mh; 12518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 12528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 12538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 12548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Binds a value {@code x} to the first argument of a method handle, without invoking it. 12558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The new method handle adapts, as its <i>target</i>, 12568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the current method handle by binding it to the given argument. 12578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The type of the bound handle will be 12588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * the same as the type of the target, except that a single leading 12598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * reference parameter will be omitted. 12608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 12618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * When called, the bound handle inserts the given value {@code x} 12628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * as a new leading argument to the target. The other arguments are 12638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * also passed unchanged. 12648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * What the target eventually returns is returned unchanged by the bound handle. 12658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 12668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * The reference {@code x} must be convertible to the first parameter 12678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * type of the target. 12688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 12698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (<em>Note:</em> Because method handles are immutable, the target method handle 12708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * retains its original type and behavior.) 12718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @param x the value to bind to the first argument of the target 12728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return a new method handle which prepends the given value to the incoming 12738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * argument list, before calling the original method handle 12748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws IllegalArgumentException if the target does not have a 12758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * leading parameter type that is a reference type 12768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @throws ClassCastException if {@code x} cannot be converted 12778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the leading parameter type of the target 12786774aff0e542cbe31c02570916ff98c6337071dfNarayan Kamath * @see MethodHandles#insertArguments 12798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 12808b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public MethodHandle bindTo(Object x) { 12818b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath x = type.leadingReferenceParameter().cast(x); // throw CCE if needed 12828b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 12830ab46853af9f5c16c877e1677d8d27b8fdecc2cdNarayan Kamath return new Transformers.BindTo(this, x); 12848b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 12858b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 12868b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath /** 12878b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Returns a string representation of the method handle, 12888b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * starting with the string {@code "MethodHandle"} and 12898b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * ending with the string representation of the method handle's type. 12908b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * In other words, this method returns a string equal to the value of: 12918b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <blockquote><pre>{@code 12928b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * "MethodHandle" + type().toString() 12938b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * }</pre></blockquote> 12948b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * <p> 12958b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * (<em>Note:</em> Future releases of this API may add further information 12968b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * to the string representation. 12978b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * Therefore, the present syntax should not be parsed by applications.) 12988b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * 12998b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath * @return a string representation of the method handle 13008b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath */ 13018b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath @Override 13028b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath public String toString() { 13038b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Android-changed: Removed debugging support. 13048b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath return "MethodHandle"+type; 13058b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath } 13068b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath 130754168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath /** @hide */ 130854168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath public int getHandleKind() { 130954168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath return handleKind; 131054168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath } 131154168f0e8137b9d2addc6e7bf723aaf1ee3fd744Narayan Kamath 1312cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath /** @hide */ 1313faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath protected void transform(EmulatedStackFrame arguments) throws Throwable { 1314faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath throw new AssertionError("MethodHandle.transform should never be called."); 1315faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath } 1316faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath 1317faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath /** 1318ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath * Creates a copy of this method handle, copying all relevant data. 1319cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath * 1320cce1c9e194b4082f00fd6aac2ef9beec75ff5500Narayan Kamath * @hide 1321ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath */ 1322ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath protected MethodHandle duplicate() { 1323ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath try { 1324ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath return (MethodHandle) this.clone(); 1325ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath } catch (CloneNotSupportedException cnse) { 1326ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath throw new AssertionError("Subclass of Transformer is not cloneable"); 1327ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath } 1328ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath } 1329ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath 1330ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath 1331ff28f8512f99a9507f12b9eb600a374414735394Narayan Kamath /** 1332faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * This is the entry point for all transform calls, and dispatches to the protected 1333faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * transform method. This layer of indirection exists purely for convenience, because 1334faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * we can invoke-direct on a fixed ArtMethod for all transform variants. 1335faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * 1336faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * NOTE: If this extra layer of indirection proves to be a problem, we can get rid 1337faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath * of this layer of indirection at the cost of some additional ugliness. 1338faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath */ 1339faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath private void transformInternal(EmulatedStackFrame arguments) throws Throwable { 1340faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath transform(arguments); 1341faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath } 1342faf8883397aed1411590edd1bf5b6681430a10f5Narayan Kamath 13438b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Android-changed: Removed implementation details : 13448b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13458b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // String standardString(); 13468b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // String debugString(); 13478b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13488b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath //// Implementation methods. 13498b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath //// Sub-classes can override these default implementations. 13508b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath //// All these methods assume arguments are already validated. 13518b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13528b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Other transforms to do: convert, explicitCast, permute, drop, filter, fold, GWT, catch 13538b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13548b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // BoundMethodHandle bindArgumentL(int pos, Object value); 13558b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ MethodHandle setVarargs(MemberName member); 13568b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ MethodHandle viewAsType(MethodType newType, boolean strict); 13578b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ boolean viewAsTypeChecks(MethodType newType, boolean strict); 13588b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13598b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // Decoding 13608b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13618b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ LambdaForm internalForm(); 13628b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ MemberName internalMemberName(); 13638b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ Class<?> internalCallerClass(); 13648b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ MethodHandleImpl.Intrinsic intrinsicName(); 13658b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ MethodHandle withInternalMemberName(MemberName member, boolean isInvokeSpecial); 13668b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ boolean isInvokeSpecial(); 13678b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ Object internalValues(); 13688b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ Object internalProperties(); 13698b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13708b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath //// Method handle implementation methods. 13718b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath //// Sub-classes can override these default implementations. 13728b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath //// All these methods assume arguments are already validated. 13738b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // 13748b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ abstract MethodHandle copyWith(MethodType mt, LambdaForm lf); 13758b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // abstract BoundMethodHandle rebind(); 13768b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ void updateForm(LambdaForm newForm); 13778b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // /*non-public*/ void customize(); 13788b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath // private static final long FORM_OFFSET; 13798b532c93d91102f2f3edf9a6b69e2ce9d2a3a8e6Narayan Kamath} 1380