invocationhandler.java

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/*
 * @(#)InvocationHandler.java	1.7 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang.reflect;

/**
 * <code>InvocationHandler</code> is the interface implemented by
 * the <i>invocation handler</i> of a proxy instance.
 *
 * <p>Each proxy instance has an associated invocation handler.
 * When a method is invoked on a proxy instance, the method
 * invocation is encoded and dispatched to the <code>invoke</code>
 * method of its invocation handler.
 *
 * @author	Peter Jones
 * @version	1.7, 03/01/23
 * @see		Proxy
 * @since	JDK1.3
 */
public interface InvocationHandler {

    /**
     * Processes a method invocation on a proxy instance and returns
     * the result.  This method will be invoked on an invocation handler
     * when a method is invoked on a proxy instance that it is
     * associated with.
     *
     * @param	proxy the proxy instance that the method was invoked on
     *
     * @param	method the <code>Method</code> instance corresponding to
     * the interface method invoked on the proxy instance.  The declaring
     * class of the <code>Method</code> object will be the interface that
     * the method was declared in, which may be a superinterface of the
     * proxy interface that the proxy class inherits the method through.
     *
     * @param	args an array of objects containing the values of the
     * arguments passed in the method invocation on the proxy instance,
     * or <code>null</code> if interface method takes no arguments.
     * Arguments of primitive types are wrapped in instances of the
     * appropriate primitive wrapper class, such as
     * <code>java.lang.Integer</code> or <code>java.lang.Boolean</code>.
     *
     * @return	the value to return from the method invocation on the
     * proxy instance.  If the declared return type of the interface
     * method is a primitive type, then the value returned by
     * this method must be an instance of the corresponding primitive
     * wrapper class; otherwise, it must be a type assignable to the
     * declared return type.  If the value returned by this method is
     * <code>null</code> and the interface method's return type is
     * primitive, then a <code>NullPointerException</code> will be
     * thrown by the method invocation on the proxy instance.  If the
     * value returned by this method is otherwise not compatible with
     * the interface method's declared return type as described above,
     * a <code>ClassCastException</code> will be thrown by the method
     * invocation on the proxy instance.
     *
     * @throws	Throwable the exception to throw from the method
     * invocation on the proxy instance.  The exception's type must be
     * assignable either to any of the exception types declared in the
     * <code>throws</code> clause of the interface method or to the
     * unchecked exception types <code>java.lang.RuntimeException</code>
     * or <code>java.lang.Error</code>.  If a checked exception is
     * thrown by this method that is not assignable to any of the
     * exception types declared in the <code>throws</code> clause of
     * the interface method, then an
     * {@link UndeclaredThrowableException} containing the
     * exception that was thrown by this method will be thrown by the
     * method invocation on the proxy instance.
     *
     * @see	UndeclaredThrowableException
     */
    public Object invoke(Object proxy, Method method, Object[] args)
	throws Throwable;
}