/* * Copyright (c) 1996, 2004, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.io; import java.io.ObjectOutput;import java.io.ObjectInput; /** * Only the identity of the class of an Externalizable instance is * written in the serialization stream and it is the responsibility * of the class to save and restore the contents of its instances. * * The writeExternal and readExternal methods of the Externalizable * interface are implemented by a class to give the class complete * control over the format and contents of the stream for an object * and its supertypes. These methods must explicitly * coordinate with the supertype to save its state. These methods supersede * customized implementations of writeObject and readObject methods.<br> * * Object Serialization uses the Serializable and Externalizable * interfaces.  Object persistence mechanisms can use them as well.  Each * object to be stored is tested for the Externalizable interface. If * the object supports Externalizable, the writeExternal method is called. If the * object does not support Externalizable and does implement * Serializable, the object is saved using * ObjectOutputStream. <br> When an Externalizable object is * reconstructed, an instance is created using the public no-arg * constructor, then the readExternal method called.  Serializable * objects are restored by reading them from an ObjectInputStream.<br> * * An Externalizable instance can designate a substitution object via * the writeReplace and readResolve methods documented in the Serializable * interface.<br> * * @author  unascribed * @see java.io.ObjectOutputStream * @see java.io.ObjectInputStream * @see java.io.ObjectOutput * @see java.io.ObjectInput * @see java.io.Serializable * @since   JDK1.1 */public interface Externalizable extends java.io.Serializable {    /**     * The object implements the writeExternal method to save its contents     * by calling the methods of DataOutput for its primitive values or     * calling the writeObject method of ObjectOutput for objects, strings,     * and arrays.     *     * @serialData Overriding methods should use this tag to describe     *             the data layout of this Externalizable object.     *             List the sequence of element types and, if possible,     *             relate the element to a public/protected field and/or     *             method of this Externalizable class.     *     * @param out the stream to write the object to     * @exception IOException Includes any I/O exceptions that may occur     */    void writeExternal(ObjectOutput out) throws IOException;     /**     * The object implements the readExternal method to restore its     * contents by calling the methods of DataInput for primitive     * types and readObject for objects, strings and arrays.  The     * readExternal method must read the values in the same sequence     * and with the same types as were written by writeExternal.     *     * @param in the stream to read data from in order to restore the object     * @exception IOException if I/O errors occur     * @exception ClassNotFoundException If the class for an object being     *              restored cannot be found.     */    void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;}