* Note that classes which implement this interface must take into account * that all superclass data must also be written to the stream as well. * The class implementing this interface must figure out how to make that * happen. *
* This interface can be used to provide object persistence. When an
* object is to be stored externally, the writeExternal method is
* called to save state. When the object is restored, an instance is
* created using the default no-argument constructor and the
* readExternal method is used to restore the state.
*
* @author Aaron M. Renn (arenn@urbanophile.com)
*/
public interface Externalizable extends Serializable
{
long serialVersionUID = -282491828744381764L;
/**
* This method restores an object's state by reading in the instance data
* for the object from the passed in stream. Note that this stream is not
* a subclass of InputStream, but rather is a class that
* implements
* the ObjectInput interface. That interface provides a
* mechanism for
* reading in Java data types from a stream.
*
* Note that this method must be compatible with writeExternal.
* It must read back the exact same types that were written by that
* method in the exact order they were written.
*
* If this method needs to read back an object instance, then the class
* for that object must be found and loaded. If that operation fails,
* then this method throws a ClassNotFoundException
*
* @param in An ObjectInput instance for reading in the object
* state
*
* @exception ClassNotFoundException If the class of an object being
* restored cannot be found
* @exception IOException If any other error occurs
*/
void readExternal(ObjectInput in)
throws ClassNotFoundException, IOException;
/**
* This method is responsible for writing the instance data of an object
* to the passed in stream. Note that this stream is not a subclass of
* OutputStream, but rather is a class that implements the
* ObjectOutput interface. That interface provides a
* number of methods
* for writing Java data values to a stream.
*
* Not that the implementation of this method must be coordinated with
* the implementation of readExternal.
*
* @param out An ObjectOutput instance for writing the
* object state
*
* @exception IOException If an error occurs
*/
void writeExternal(ObjectOutput out) throws IOException;
}