javaunohelper/com/sun/star/lib/uno/helper/WeakAdapter.java

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  27
  28 package com.sun.star.lib.uno.helper;
  29 import java.lang.ref.WeakReference;
  30 import com.sun.star.uno.XAdapter;
  31 import com.sun.star.uno.XReference;
  32 import java.util.List;
  33 import java.util.Collections;
  34 import java.util.LinkedList;
  35
  36 /** An XAdapter implementation that holds a weak reference (java.lang.ref.WeakReference)
  37  *  to an object. Clients can register listener (com.sun.star.lang.XReference) which
  38  *  are notified when the the object (the one which is kept weak) is being finalized. That
  39  *  is, that object is being destroyed because there are not any hard references
  40  *  to it.
  41  */
  42 public class WeakAdapter implements XAdapter
  43 {
  44     private final boolean DEBUG= false;
  45     // references the XWeak implementation
  46     private WeakReference m_weakRef;
  47     // contains XReference objects registered by addReference
  48     private List m_xreferenceList;
  49
  50     /**
  51      *@param component the object that is to be held weak
  52      */
  53     public WeakAdapter(Object component)
  54     {
  55         m_weakRef= new WeakReference(component);
  56         m_xreferenceList= Collections.synchronizedList( new LinkedList());
  57     }
  58
  59     /** Called by the XWeak implementation (WeakBase) when it is being finalized.
  60      *  It is only being called once.
  61      *  The registererd XReference listeners are notified. On notification they are
  62      *  to unregister themselves. The notification is thread-safe. However, it is possible
  63      *  to add a listener during the notification process, which will never receive a
  64      *  notification. To prevent this, one would have to synchronize this method with
  65      *  the addReference method. But this can result in deadlocks in a multithreaded
  66      *  environment.
  67      */
  68     void referentDying()
  69     {
  70         //synchronized call
  71         Object[] references= m_xreferenceList.toArray();
  72         for (int i= references.length; i > 0; i--)
  73         {
  74             ((XReference) references[i-1]).dispose();
  75         }
  76     }
  77
  78     /** Method  of com.sun.star.uno.XAdapter. It is called to obtain a hard reference
  79      *  to the object which is kept weak by this instance.
  80      *  @return hard reference to the object
  81      */
  82     public Object queryAdapted()
  83     {
  84         return m_weakRef.get();
  85     }
  86     /** Method of com.sun.star.uno.XAdapter. Called by clients to register listener which
  87      * are notified when the weak object is dying.
  88      *@param xReference a listener
  89      */
  90     public void removeReference(XReference xReference)
  91     {
  92         m_xreferenceList.remove(xReference);
  93     }
  94     /** Method of com.sun.star.uno.XAdapter. Called by clients to unregister listeners.
  95      *@param a listener
  96      */
  97     public void addReference(XReference xReference)
  98     {
  99         m_xreferenceList.add(xReference);
 100     }
 101 }
 102