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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