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3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5    * This code is free software; you can redistribute it and/or modify it
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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
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19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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       */
93      public Object invoke(Object proxy, Method method, Object[] args)
94          throws Throwable;
95  }