1 /* 2 * Copyright (c) 1999, 2006, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang.reflect; 27 28 /** 29 * {@code InvocationHandler} is the interface implemented by 30 * the <i>invocation handler</i> of a proxy instance. 31 * 32 * <p>Each proxy instance has an associated invocation handler. 33 * When a method is invoked on a proxy instance, the method 34 * invocation is encoded and dispatched to the {@code invoke} 35 * method of its invocation handler. 36 * 37 * @author Peter Jones 38 * @see Proxy 39 * @since 1.3 40 */ 41 public interface InvocationHandler { 42 43 /** 44 * Processes a method invocation on a proxy instance and returns 45 * the result. This method will be invoked on an invocation handler 46 * when a method is invoked on a proxy instance that it is 47 * associated with. 48 * 49 * @param proxy the proxy instance that the method was invoked on 50 * 51 * @param method the {@code Method} instance corresponding to 52 * the interface method invoked on the proxy instance. The declaring 53 * class of the {@code Method} object will be the interface that 54 * the method was declared in, which may be a superinterface of the 55 * proxy interface that the proxy class inherits the method through. 56 * 57 * @param args an array of objects containing the values of the 58 * arguments passed in the method invocation on the proxy instance, 59 * or {@code null} if interface method takes no arguments. 60 * Arguments of primitive types are wrapped in instances of the 61 * appropriate primitive wrapper class, such as 62 * {@code java.lang.Integer} or {@code java.lang.Boolean}. 63 * 64 * @return the value to return from the method invocation on the 65 * proxy instance. If the declared return type of the interface 66 * method is a primitive type, then the value returned by 67 * this method must be an instance of the corresponding primitive 68 * wrapper class; otherwise, it must be a type assignable to the 69 * declared return type. If the value returned by this method is 70 * {@code null} and the interface method's return type is 71 * primitive, then a {@code NullPointerException} will be 72 * thrown by the method invocation on the proxy instance. If the 73 * value returned by this method is otherwise not compatible with 74 * the interface method's declared return type as described above, 75 * a {@code ClassCastException} will be thrown by the method 76 * invocation on the proxy instance. 77 * 78 * @throws Throwable the exception to throw from the method 79 * invocation on the proxy instance. The exception's type must be 80 * assignable either to any of the exception types declared in the 81 * {@code throws} clause of the interface method or to the 82 * unchecked exception types {@code java.lang.RuntimeException} 83 * or {@code java.lang.Error}. If a checked exception is 84 * thrown by this method that is not assignable to any of the 85 * exception types declared in the {@code throws} clause of 86 * the interface method, then an 87 * {@link UndeclaredThrowableException} containing the 88 * exception that was thrown by this method will be thrown by the 89 * method invocation on the proxy instance. 90 * 91 * @see UndeclaredThrowableException 92 */ invoke(Object proxy, Method method, Object[] args)93 public Object invoke(Object proxy, Method method, Object[] args) 94 throws Throwable; 95 } 96