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1   /*
2    * Copyright (c) 1996, 2013, 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  
26  package java.io;
27  
28  /**
29   * Serializability of a class is enabled by the class implementing the
30   * java.io.Serializable interface. Classes that do not implement this
31   * interface will not have any of their state serialized or
32   * deserialized.  All subtypes of a serializable class are themselves
33   * serializable.  The serialization interface has no methods or fields
34   * and serves only to identify the semantics of being serializable. <p>
35   *
36   * To allow subtypes of non-serializable classes to be serialized, the
37   * subtype may assume responsibility for saving and restoring the
38   * state of the supertype's public, protected, and (if accessible)
39   * package fields.  The subtype may assume this responsibility only if
40   * the class it extends has an accessible no-arg constructor to
41   * initialize the class's state.  It is an error to declare a class
42   * Serializable if this is not the case.  The error will be detected at
43   * runtime. <p>
44   *
45   * During deserialization, the fields of non-serializable classes will
46   * be initialized using the public or protected no-arg constructor of
47   * the class.  A no-arg constructor must be accessible to the subclass
48   * that is serializable.  The fields of serializable subclasses will
49   * be restored from the stream. <p>
50   *
51   * When traversing a graph, an object may be encountered that does not
52   * support the Serializable interface. In this case the
53   * NotSerializableException will be thrown and will identify the class
54   * of the non-serializable object. <p>
55   *
56   * Classes that require special handling during the serialization and
57   * deserialization process must implement special methods with these exact
58   * signatures:
59   *
60   * <PRE>
61   * private void writeObject(java.io.ObjectOutputStream out)
62   *     throws IOException
63   * private void readObject(java.io.ObjectInputStream in)
64   *     throws IOException, ClassNotFoundException;
65   * private void readObjectNoData()
66   *     throws ObjectStreamException;
67   * </PRE>
68   *
69   * <p>The writeObject method is responsible for writing the state of the
70   * object for its particular class so that the corresponding
71   * readObject method can restore it.  The default mechanism for saving
72   * the Object's fields can be invoked by calling
73   * out.defaultWriteObject. The method does not need to concern
74   * itself with the state belonging to its superclasses or subclasses.
75   * State is saved by writing the individual fields to the
76   * ObjectOutputStream using the writeObject method or by using the
77   * methods for primitive data types supported by DataOutput.
78   *
79   * <p>The readObject method is responsible for reading from the stream and
80   * restoring the classes fields. It may call in.defaultReadObject to invoke
81   * the default mechanism for restoring the object's non-static and
82   * non-transient fields.  The defaultReadObject method uses information in
83   * the stream to assign the fields of the object saved in the stream with the
84   * correspondingly named fields in the current object.  This handles the case
85   * when the class has evolved to add new fields. The method does not need to
86   * concern itself with the state belonging to its superclasses or subclasses.
87   * State is saved by writing the individual fields to the
88   * ObjectOutputStream using the writeObject method or by using the
89   * methods for primitive data types supported by DataOutput.
90   *
91   * <p>The readObjectNoData method is responsible for initializing the state of
92   * the object for its particular class in the event that the serialization
93   * stream does not list the given class as a superclass of the object being
94   * deserialized.  This may occur in cases where the receiving party uses a
95   * different version of the deserialized instance's class than the sending
96   * party, and the receiver's version extends classes that are not extended by
97   * the sender's version.  This may also occur if the serialization stream has
98   * been tampered; hence, readObjectNoData is useful for initializing
99   * deserialized objects properly despite a "hostile" or incomplete source
100  * stream.
101  *
102  * <p>Serializable classes that need to designate an alternative object to be
103  * used when writing an object to the stream should implement this
104  * special method with the exact signature:
105  *
106  * <PRE>
107  * ANY-ACCESS-MODIFIER Object writeReplace() throws ObjectStreamException;
108  * </PRE><p>
109  *
110  * This writeReplace method is invoked by serialization if the method
111  * exists and it would be accessible from a method defined within the
112  * class of the object being serialized. Thus, the method can have private,
113  * protected and package-private access. Subclass access to this method
114  * follows java accessibility rules. <p>
115  *
116  * Classes that need to designate a replacement when an instance of it
117  * is read from the stream should implement this special method with the
118  * exact signature.
119  *
120  * <PRE>
121  * ANY-ACCESS-MODIFIER Object readResolve() throws ObjectStreamException;
122  * </PRE><p>
123  *
124  * This readResolve method follows the same invocation rules and
125  * accessibility rules as writeReplace.<p>
126  *
127  * The serialization runtime associates with each serializable class a version
128  * number, called a serialVersionUID, which is used during deserialization to
129  * verify that the sender and receiver of a serialized object have loaded
130  * classes for that object that are compatible with respect to serialization.
131  * If the receiver has loaded a class for the object that has a different
132  * serialVersionUID than that of the corresponding sender's class, then
133  * deserialization will result in an {@link InvalidClassException}.  A
134  * serializable class can declare its own serialVersionUID explicitly by
135  * declaring a field named <code>"serialVersionUID"</code> that must be static,
136  * final, and of type <code>long</code>:
137  *
138  * <PRE>
139  * ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L;
140  * </PRE>
141  *
142  * If a serializable class does not explicitly declare a serialVersionUID, then
143  * the serialization runtime will calculate a default serialVersionUID value
144  * for that class based on various aspects of the class, as described in the
145  * Java(TM) Object Serialization Specification.  However, it is <em>strongly
146  * recommended</em> that all serializable classes explicitly declare
147  * serialVersionUID values, since the default serialVersionUID computation is
148  * highly sensitive to class details that may vary depending on compiler
149  * implementations, and can thus result in unexpected
150  * <code>InvalidClassException</code>s during deserialization.  Therefore, to
151  * guarantee a consistent serialVersionUID value across different java compiler
152  * implementations, a serializable class must declare an explicit
153  * serialVersionUID value.  It is also strongly advised that explicit
154  * serialVersionUID declarations use the <code>private</code> modifier where
155  * possible, since such declarations apply only to the immediately declaring
156  * class--serialVersionUID fields are not useful as inherited members. Array
157  * classes cannot declare an explicit serialVersionUID, so they always have
158  * the default computed value, but the requirement for matching
159  * serialVersionUID values is waived for array classes.
160  *
161  * @author  unascribed
162  * @see java.io.ObjectOutputStream
163  * @see java.io.ObjectInputStream
164  * @see java.io.ObjectOutput
165  * @see java.io.ObjectInput
166  * @see java.io.Externalizable
167  * @since   JDK1.1
168  */
169 public interface Serializable {
170 }