01 /*
02 * Copyright 1996-2004 Sun Microsystems, Inc. All Rights Reserved.
03 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
04 *
05 * This code is free software; you can redistribute it and/or modify it
06 * under the terms of the GNU General Public License version 2 only, as
07 * published by the Free Software Foundation. Sun designates this
08 * particular file as subject to the "Classpath" exception as provided
09 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package java.io;
27
28 import java.io.ObjectOutput;
29 import 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 * @version 1.26, 05/05/07
60 * @see java.io.ObjectOutputStream
61 * @see java.io.ObjectInputStream
62 * @see java.io.ObjectOutput
63 * @see java.io.ObjectInput
64 * @see java.io.Serializable
65 * @since JDK1.1
66 */
67 public interface Externalizable extends java.io.Serializable {
68 /**
69 * The object implements the writeExternal method to save its contents
70 * by calling the methods of DataOutput for its primitive values or
71 * calling the writeObject method of ObjectOutput for objects, strings,
72 * and arrays.
73 *
74 * @serialData Overriding methods should use this tag to describe
75 * the data layout of this Externalizable object.
76 * List the sequence of element types and, if possible,
77 * relate the element to a public/protected field and/or
78 * method of this Externalizable class.
79 *
80 * @param out the stream to write the object to
81 * @exception IOException Includes any I/O exceptions that may occur
82 */
83 void writeExternal(ObjectOutput out) throws IOException;
84
85 /**
86 * The object implements the readExternal method to restore its
87 * contents by calling the methods of DataInput for primitive
88 * types and readObject for objects, strings and arrays. The
89 * readExternal method must read the values in the same sequence
90 * and with the same types as were written by writeExternal.
91 *
92 * @param in the stream to read data from in order to restore the object
93 * @exception IOException if I/O errors occur
94 * @exception ClassNotFoundException If the class for an object being
95 * restored cannot be found.
96 */
97 void readExternal(ObjectInput in) throws IOException,
98 ClassNotFoundException;
99 }
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