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<title>
  Interface java.io.Externalizable
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<h1>
  Interface java.io.Externalizable
</h1>
<dl>
  <dt> public interface <b>Externalizable</b>
  <dt> extends <a href="java.io.Serializable.html#_top_">Serializable</a>
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Externalization allows a class to specify the methods to be used to
 write the object's contents to a stream and to read them back.  The
 Externalizable interface's writeExternal and readExternal methods
 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. <br>
 Object Serialization uses the Serializable and Externalizable
 interfaces.  Object persistence mechanisms may use them also.  Each
 object to be stored is tested for the Externalizable interface. If
 the object supports it, the writeExternal method is called. If the
 object does not support Externalizable and does implement
 Serializable the object should be saved using
 ObjectOutputStream. <br> When an Externalizable object is to be
 reconstructed, an instance is created using the public no-arg
 constructor and the readExternal method called.  Serializable
 objects are restored by reading them from an ObjectInputStream.
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    <dt> <b>See Also:</b>
    <dd> <a href="java.io.ObjectOutputStream.html#_top_">ObjectOutputStream</a>, <a href="java.io.ObjectInputStream.html#_top_">ObjectInputStream</a>, <a href="java.io.ObjectOutput.html#_top_">ObjectOutput</a>, <a href="java.io.ObjectInput.html#_top_">ObjectInput</a>, <a href="java.io.Serializable.html#_top_">Serializable</a>
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  <img src="images/method-index.gif" width=207 height=38 alt="Method Index">
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  <dt> <img src="images/red-ball-small.gif" width=6 height=6 alt=" o ">
	<a href="#readExternal(java.io.ObjectInput)"><b>readExternal</b></a>(ObjectInput)
  <dd>  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.
  <dt> <img src="images/red-ball-small.gif" width=6 height=6 alt=" o ">
	<a href="#writeExternal(java.io.ObjectOutput)"><b>writeExternal</b></a>(ObjectOutput)
  <dd>  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.
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  <img src="images/methods.gif" width=151 height=38 alt="Methods">
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<a name="writeExternal(java.io.ObjectOutput)"><img src="images/red-ball.gif" width=12 height=12 alt=" o "></a>
<a name="writeExternal"><b>writeExternal</b></a>
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 public abstract void writeExternal(<a href="java.io.ObjectOutput.html#_top_">ObjectOutput</a> out) throws <a href="java.io.IOException.html#_top_">IOException</a>
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<dl>
  <dd> 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.
<p>
  <dd><dl>
    <dt> <b>Throws:</b> <a href="java.io.IOException.html#_top_">IOException</a>
    <dd> Includes any I/O exceptions that may occur
  </dl></dd>
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<a name="readExternal(java.io.ObjectInput)"><img src="images/red-ball.gif" width=12 height=12 alt=" o "></a>
<a name="readExternal"><b>readExternal</b></a>
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 public abstract void readExternal(<a href="java.io.ObjectInput.html#_top_">ObjectInput</a> in) throws <a href="java.io.IOException.html#_top_">IOException</a>, <a href="java.lang.ClassNotFoundException.html#_top_">ClassNotFoundException</a>
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<dl>
  <dd> 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.
<p>
  <dd><dl>
    <dt> <b>Throws:</b> <a href="java.lang.ClassNotFoundException.html#_top_">ClassNotFoundException</a>
    <dd> If the class for an object being
              restored cannot be found.
  </dl></dd>
</dl>
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