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| 1 | +/* | |
| 2 | + * Copyright (c) 1996, 2005, 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: <p> | |
| 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: <p> | |
| 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.<p> | |
| 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>:<p> | |
| 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 | +} | |