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 *
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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24 */
25
26package 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 */
41public 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     */
93    public Object invoke(Object proxy, Method method, Object[] args)
94        throws Throwable;
95}
96