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/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* This file incorporates work covered by the following license notice:
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed
* with this work for additional information regarding copyright
* ownership. The ASF licenses this file to you under the Apache
* License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0 .
*/
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.
*
* <p>It actually holds a reference to a <code>com.sun.star.XAdapter</code>
* implementation and obtains a hard reference if necessary.
*/
public class WeakReference
{
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= UnoRuntime.queryInterface(XWeak.class, weakImpl);
if (weak != null)
{
XAdapter adapter= 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= UnoRuntime.queryInterface(XWeak.class, obj);
if (weak != null)
{
XAdapter adapter= 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.
*
* <p>It keeps the XAdapter implementation and registers always with it.
* Deregistering occurs on notification by the adapter and the adapter is
* released.</p>
*/
class OWeakRefListener implements XReference
{
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 <code>com.sun.star.uno.XReference</code>.
*
* <p>When called, it deregisteres this object with the adapter and releases
* the reference to it.</p>
*/
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;
}
}
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