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Externalizable.java
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/*
* Copyright (c) 1996, 2004, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.io;
import java.io.ObjectOutput;
import java.io.ObjectInput;
/**
* Only the identity of the class of an Externalizable instance is
* written in the serialization stream and it is the responsibility
* of the class to save and restore the contents of its instances.
*
* The writeExternal and readExternal methods of the Externalizable
* interface are implemented by a class to give the class complete
* control over the format and contents of the stream for an object
* and its supertypes. These methods must explicitly
* coordinate with the supertype to save its state. These methods supersede
* customized implementations of writeObject and readObject methods.<br>
*
* Object Serialization uses the Serializable and Externalizable
* interfaces. Object persistence mechanisms can use them as well. Each
* object to be stored is tested for the Externalizable interface. If
* the object supports Externalizable, the writeExternal method is called. If the
* object does not support Externalizable and does implement
* Serializable, the object is saved using
* ObjectOutputStream. <br> When an Externalizable object is
* reconstructed, an instance is created using the public no-arg
* constructor, then the readExternal method called. Serializable
* objects are restored by reading them from an ObjectInputStream.<br>
*
* An Externalizable instance can designate a substitution object via
* the writeReplace and readResolve methods documented in the Serializable
* interface.<br>
*
* @author unascribed
* @see java.io.ObjectOutputStream
* @see java.io.ObjectInputStream
* @see java.io.ObjectOutput
* @see java.io.ObjectInput
* @see java.io.Serializable
* @since JDK1.1
*/
public interface Externalizable extends java.io.Serializable {
/**
* The object implements the writeExternal method to save its contents
* by calling the methods of DataOutput for its primitive values or
* calling the writeObject method of ObjectOutput for objects, strings,
* and arrays.
*
* @serialData Overriding methods should use this tag to describe
* the data layout of this Externalizable object.
* List the sequence of element types and, if possible,
* relate the element to a public/protected field and/or
* method of this Externalizable class.
*
* @param out the stream to write the object to
* @exception IOException Includes any I/O exceptions that may occur
*/
void writeExternal(ObjectOutput out) throws IOException;
/**
* The object implements the readExternal method to restore its
* contents by calling the methods of DataInput for primitive
* types and readObject for objects, strings and arrays. The
* readExternal method must read the values in the same sequence
* and with the same types as were written by writeExternal.
*
* @param in the stream to read data from in order to restore the object
* @exception IOException if I/O errors occur
* @exception ClassNotFoundException If the class for an object being
* restored cannot be found.
*/
void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;
}