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Top Description Methods
java.io

public Interface Externalizable

extends Serializable
Known Direct Implementers
java.time.Ser, java.time.chrono.Ser, java.time.zone.Ser, java.util.LinkedList.ReverseOrderLinkedListView
Imports
java.io.ObjectOutput, .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.
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.
Since
1.1
See Also
java.io.ObjectOutputStream, java.io.ObjectInputStream, java.io.ObjectOutput, java.io.ObjectInput, java.io.Serializable

Method Summary

Modifier and TypeMethod and Description
public void
readExternal(ObjectInput
the stream to read data from in order to restore the object
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.

public void
writeExternal(ObjectOutput
the stream to write the object to
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.

Method Detail

readExternalback to summary
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException

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.

Parameters
in:ObjectInput

the stream to read data from in order to restore the object

Exceptions
IOException:
if I/O errors occur
ClassNotFoundException:
If the class for an object being restored cannot be found.
writeExternalback to summary
public void writeExternal(ObjectOutput out) throws IOException

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.

Parameters
out:ObjectOutput

the stream to write the object to

Exceptions
IOException:
Includes any I/O exceptions that may occur
Serial data
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.