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 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 * @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 JDK1.1 65 */ 66 public 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 */ writeExternal(ObjectOutput out)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 */ readExternal(ObjectInput in)96 void readExternal(ObjectInput in) throws IOException, ClassNotFoundException; 97 } 98