108 lines
4.6 KiB
Java
108 lines
4.6 KiB
Java
/* Externalizable.java -- Interface for saving and restoring object data
|
|
Copyright (C) 1998 Free Software Foundation, Inc.
|
|
|
|
This file is part of GNU Classpath.
|
|
|
|
GNU Classpath is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2, or (at your option)
|
|
any later version.
|
|
|
|
GNU Classpath is distributed in the hope that it will be useful, but
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with GNU Classpath; see the file COPYING. If not, write to the
|
|
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
|
|
02110-1301 USA.
|
|
|
|
Linking this library statically or dynamically with other modules is
|
|
making a combined work based on this library. Thus, the terms and
|
|
conditions of the GNU General Public License cover the whole
|
|
combination.
|
|
|
|
As a special exception, the copyright holders of this library give you
|
|
permission to link this library with independent modules to produce an
|
|
executable, regardless of the license terms of these independent
|
|
modules, and to copy and distribute the resulting executable under
|
|
terms of your choice, provided that you also meet, for each linked
|
|
independent module, the terms and conditions of the license of that
|
|
module. An independent module is a module which is not derived from
|
|
or based on this library. If you modify this library, you may extend
|
|
this exception to your version of the library, but you are not
|
|
obligated to do so. If you do not wish to do so, delete this
|
|
exception statement from your version. */
|
|
|
|
|
|
package java.io;
|
|
|
|
/**
|
|
* This interface provides a way that classes can completely control how
|
|
* the data of their object instances are written and read to and from
|
|
* streams. It has two methods which are used to write the data to a stream
|
|
* and to read the data from a stream. The read method must read the data
|
|
* in exactly the way it was written by the write method.
|
|
* <p>
|
|
* 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.
|
|
* <p>
|
|
* This interface can be used to provide object persistence. When an
|
|
* object is to be stored externally, the <code>writeExternal</code> method is
|
|
* called to save state. When the object is restored, an instance is
|
|
* created using the default no-argument constructor and the
|
|
* <code>readExternal</code> method is used to restore the state.
|
|
*
|
|
* @author Aaron M. Renn (arenn@urbanophile.com)
|
|
*/
|
|
public interface Externalizable extends Serializable
|
|
{
|
|
/**
|
|
* 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 <code>InputStream</code>, but rather is a class that
|
|
* implements
|
|
* the <code>ObjectInput</code> interface. That interface provides a
|
|
* mechanism for
|
|
* reading in Java data types from a stream.
|
|
* <p>
|
|
* Note that this method must be compatible with <code>writeExternal</code>.
|
|
* It must read back the exact same types that were written by that
|
|
* method in the exact order they were written.
|
|
* <p>
|
|
* 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 <code>ClassNotFoundException</code>
|
|
*
|
|
* @param in An <code>ObjectInput</code> 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
|
|
* <code>OutputStream</code>, but rather is a class that implements the
|
|
* <code>ObjectOutput</code> interface. That interface provides a
|
|
* number of methods
|
|
* for writing Java data values to a stream.
|
|
* <p>
|
|
* Not that the implementation of this method must be coordinated with
|
|
* the implementation of <code>readExternal</code>.
|
|
*
|
|
* @param out An <code>ObjectOutput</code> instance for writing the
|
|
* object state
|
|
*
|
|
* @exception IOException If an error occurs
|
|
*/
|
|
void writeExternal(ObjectOutput out) throws IOException;
|
|
}
|