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110 lines
4.7 KiB
Java
110 lines
4.7 KiB
Java
/* Externalizable.java -- Interface for saving and restoring object data
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Copyright (C) 1998 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.io;
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/**
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* This interface provides a way that classes can completely control how
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* the data of their object instances are written and read to and from
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* streams. It has two methods which are used to write the data to a stream
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* and to read the data from a stream. The read method must read the data
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* in exactly the way it was written by the write method.
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* <p>
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* Note that classes which implement this interface must take into account
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* that all superclass data must also be written to the stream as well.
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* The class implementing this interface must figure out how to make that
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* happen.
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* <p>
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* This interface can be used to provide object persistence. When an
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* object is to be stored externally, the <code>writeExternal</code> method is
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* called to save state. When the object is restored, an instance is
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* created using the default no-argument constructor and the
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* <code>readExternal</code> method is used to restore the state.
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*
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* @version 0.0
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*
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* @author Aaron M. Renn (arenn@urbanophile.com)
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*/
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public interface Externalizable extends Serializable
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{
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/**
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* This method restores an object's state by reading in the instance data
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* for the object from the passed in stream. Note that this stream is not
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* a subclass of <code>InputStream</code>, but rather is a class that implements
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* the <code>ObjectInput</code> interface. That interface provides a mechanism for
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* reading in Java data types from a stream.
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* <p>
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* Note that this method must be compatible with <code>writeExternal</code>.
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* It must read back the exact same types that were written by that
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* method in the exact order they were written.
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* <p>
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* If this method needs to read back an object instance, then the class
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* for that object must be found and loaded. If that operation fails,
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* then this method throws a <code>ClassNotFoundException</code>
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*
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* @param in An <code>ObjectInput</code> instance for reading in the object state
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*
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* @exception ClassNotFoundException If the class of an object being restored cannot be found
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* @exception IOException If any other error occurs
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*/
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public abstract void
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readExternal(ObjectInput in) throws ClassNotFoundException, IOException;
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/*************************************************************************/
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/**
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* This method is responsible for writing the instance data of an object
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* to the passed in stream. Note that this stream is not a subclass of
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* <code>OutputStream</code>, but rather is a class that implements the
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* <code>ObjectOutput</code> interface. That interface provides a number of methods
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* for writing Java data values to a stream.
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* <p>
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* Not that the implementation of this method must be coordinated with
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* the implementation of <code>readExternal</code>.
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*
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* @param out An <code>ObjectOutput</code> instance for writing the object state
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*
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* @exception IOException If an error occurs
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*/
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public abstract void
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writeExternal(ObjectOutput out) throws IOException;
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} // interface Externalizable
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