Initial revision

From-SVN: r102074

libjava/classpath/java/io/Externalizable.java

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+/* 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;
+}