externalizable.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 101 行

/*
 * @(#)Externalizable.java	1.22 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program 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.   
 *   
 * This program 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 at /legal/license.txt).   
 *   
 * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.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 supercede
 * 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
 * @version 1.15, 02/02/00
 * @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;
}