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Externalizable.java API Doc Java SE 5 API 3476 Fri Aug 26 14:56:58 BST 2005 java.io

Externalizable

public interface Externalizable implements Serializable

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.
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.
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.
An Externalizable instance can designate a substitution object via the writeReplace and readResolve methods documented in the Serializable interface.

author: unascribed
version: 1.19, 01/12/04
see: java.io.ObjectOutputStream
see: java.io.ObjectInputStream
see: java.io.ObjectOutput
see: java.io.ObjectInput
see: java.io.Serializable
since: JDK1.1

Fields Summary
Constructors Summary
Methods Summary
public void readExternal(java.io.ObjectInput in)
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.
public void writeExternal(java.io.ObjectOutput out)
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