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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= 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= 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;
}
}