/*************************************************************************
*
* $RCSfile: WeakReference.java,v $
*
* $Revision: 1.1 $
*
* last change: $Author: jl $ $Date: 2002/04/11 15:41:03 $
*
* The Contents of this file are made available subject to the terms of
* either of the following licenses
*
* - GNU Lesser General Public License Version 2.1
* - Sun Industry Standards Source License Version 1.1
*
* Sun Microsystems Inc., October, 2000
*
* GNU Lesser General Public License Version 2.1
* =============================================
* Copyright 2000 by Sun Microsystems, Inc.
* 901 San Antonio Road, Palo Alto, CA 94303, USA
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 2.1, as published by the Free Software Foundation.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*
*
* Sun Industry Standards Source License Version 1.1
* =================================================
* The contents of this file are subject to the Sun Industry Standards
* Source License Version 1.1 (the "License"); You may not use this file
* except in compliance with the License. You may obtain a copy of the
* License at http://www.openoffice.org/license.html.
*
* Software provided under this License is provided on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING,
* WITHOUT LIMITATION, WARRANTIES THAT THE SOFTWARE IS FREE OF DEFECTS,
* MERCHANTABLE, FIT FOR A PARTICULAR PURPOSE, OR NON-INFRINGING.
* See the License for the specific provisions governing your rights and
* obligations concerning the Software.
*
* The Initial Developer of the Original Code is: Sun Microsystems, Inc.
*
* Copyright: 2000 by Sun Microsystems, Inc.
*
* All Rights Reserved.
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* Contributor(s): _______________________________________
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*
************************************************************************/
package com.sun.star.uno;
import com.sun.star.uno.XWeak;
import com.sun.star.uno.UnoRuntime;
import com.sun.star.uno.XAdapter;
import com.sun.star.uno.XReference;
/** This class holds weak reference to an object. It actually holds a reference to a
com.sun.star.XAdapter implementation and obtains a hard reference if necessary.
*/
public class WeakReference
{
private final boolean DEBUG= false;
private OWeakRefListener m_listener;
// There is no default constructor. Every instance must register itself with the
// XAdapter interface, which is done in the constructors. Assume we have this code
// WeakReference ref= new WeakReference();
// ref = someOtherWeakReference;
//
// ref would not be notified (XReference.dispose()) because it did not register
// itself. Therefore the XAdapter would be kept aliver although this is not
// necessary.
/** Creates an instance of this class.
*@param obj - another instance that is to be copied
*/
public WeakReference(WeakReference obj)
{
if (obj != null)
{
Object weakImpl= obj.get();
if (weakImpl != null)
{
XWeak weak= (XWeak) UnoRuntime.queryInterface(XWeak.class, weakImpl);
if (weak != null)
{
XAdapter adapter= (XAdapter) weak.queryAdapter();
if (adapter != null)
m_listener= new OWeakRefListener(adapter);
}
}
}
}
/** Creates an instance of this class.
*@param obj XWeak implementation
*/
public WeakReference(Object obj)
{
XWeak weak= (XWeak) UnoRuntime.queryInterface(XWeak.class, obj);
if (weak != null)
{
XAdapter adapter= (XAdapter) weak.queryAdapter();
if (adapter != null)
m_listener= new OWeakRefListener(adapter);
}
}
/** Returns a hard reference to the object that is kept weak by this class.
*@return a hard reference to the XWeak implementation.
*/
public Object get()
{
if (m_listener != null)
return m_listener.get();
return null;
}
}
/** Implementation of com.sun.star.uno.XReference for use with WeakReference.
* It keeps the XAdapter implementation and registers always with it. Deregistering
* occurs on notification by the adapter and the adapter is released.
*/
class OWeakRefListener implements XReference
{
private final boolean DEBUG= false;
private XAdapter m_adapter;
/** The constructor registered this object with adapter.
*@param adapter the XAdapter implementation.
*/
OWeakRefListener( XAdapter adapter)
{
m_adapter= adapter;
m_adapter.addReference(this);
}
/** Method of com.sun.star.uno.XReference. When called, it deregisteres this
* object with the adapter and releases the reference to it.
*/
synchronized public void dispose()
{
if (m_adapter != null)
{
m_adapter.removeReference(this);
m_adapter= null;
}
}
/** Obtains a hard reference to the object which is kept weak by the adapter
* and returns it.
* @return hard reference to the otherwise weakly kept object.
*/
synchronized Object get()
{
Object retVal= null;
if (m_adapter != null)
{
retVal= m_adapter.queryAdapted();
if (retVal == null)
{
// If this object registered as listener with XAdapter while it was notifying
// the listeners then this object might not have been notified. If queryAdapted
// returned null then the weak kept object is dead and the listeners have already
// been notified. And we missed it.
m_adapter.removeReference(this);
m_adapter= null;
}
}
return retVal;
}
}