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    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        */
   93       public Object invoke(Object proxy, Method method, Object[] args)
   94           throws Throwable;
   95   }

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