1/*
2 * Copyright (c) 1996, 2004, 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
26package java.io;
27
28import java.io.ObjectOutput;
29import java.io.ObjectInput;
30
31/**
32 * Only the identity of the class of an Externalizable instance is
33 * written in the serialization stream and it is the responsibility
34 * of the class to save and restore the contents of its instances.
35 *
36 * The writeExternal and readExternal methods of the Externalizable
37 * interface are implemented by a class to give the class complete
38 * control over the format and contents of the stream for an object
39 * and its supertypes. These methods must explicitly
40 * coordinate with the supertype to save its state. These methods supersede
41 * customized implementations of writeObject and readObject methods.<br>
42 *
43 * Object Serialization uses the Serializable and Externalizable
44 * interfaces.  Object persistence mechanisms can use them as well.  Each
45 * object to be stored is tested for the Externalizable interface. If
46 * the object supports Externalizable, the writeExternal method is called. If the
47 * object does not support Externalizable and does implement
48 * Serializable, the object is saved using
49 * ObjectOutputStream. <br> When an Externalizable object is
50 * reconstructed, an instance is created using the public no-arg
51 * constructor, then the readExternal method called.  Serializable
52 * objects are restored by reading them from an ObjectInputStream.<br>
53 *
54 * An Externalizable instance can designate a substitution object via
55 * the writeReplace and readResolve methods documented in the Serializable
56 * interface.<br>
57 *
58 * @author  unascribed
59 * @see java.io.ObjectOutputStream
60 * @see java.io.ObjectInputStream
61 * @see java.io.ObjectOutput
62 * @see java.io.ObjectInput
63 * @see java.io.Serializable
64 * @since   1.1
65 */
66public interface Externalizable extends java.io.Serializable {
67    /**
68     * The object implements the writeExternal method to save its contents
69     * by calling the methods of DataOutput for its primitive values or
70     * calling the writeObject method of ObjectOutput for objects, strings,
71     * and arrays.
72     *
73     * @serialData Overriding methods should use this tag to describe
74     *             the data layout of this Externalizable object.
75     *             List the sequence of element types and, if possible,
76     *             relate the element to a public/protected field and/or
77     *             method of this Externalizable class.
78     *
79     * @param out the stream to write the object to
80     * @exception IOException Includes any I/O exceptions that may occur
81     */
82    void writeExternal(ObjectOutput out) throws IOException;
83
84    /**
85     * The object implements the readExternal method to restore its
86     * contents by calling the methods of DataInput for primitive
87     * types and readObject for objects, strings and arrays.  The
88     * readExternal method must read the values in the same sequence
89     * and with the same types as were written by writeExternal.
90     *
91     * @param in the stream to read data from in order to restore the object
92     * @exception IOException if I/O errors occur
93     * @exception ClassNotFoundException If the class for an object being
94     *              restored cannot be found.
95     */
96    void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;
97}
98