Examples of java.lang.ref.WeakReference

java.lang.ref.WeakReference
Weak reference objects, which do not prevent their referents from being made finalizable, finalized, and then reclaimed. Weak references are most often used to implement canonicalizing mappings.
Suppose that the garbage collector determines at a certain point in time that an object is weakly reachable. At that time it will atomically clear all weak references to that object and all weak references to any other weakly-reachable objects from which that object is reachable through a chain of strong and soft references. At the same time it will declare all of the formerly weakly-reachable objects to be finalizable. At the same time or at some later time it will enqueue those newly-cleared weak references that are registered with reference queues. @version 1.19, 11/17/05 @author Mark Reinhold @since 1.2

   
   /** @param callback The handle to callback a client (is checked already to be not null) */
   Container(boolean useWeakReference, I_Timeout callback, Object userData) {
      this.useWeakReference = useWeakReference;
      if (this.useWeakReference) {
         this.callback = new WeakReference(callback);
         if (userData != null) 
            this.userData = new WeakReference(userData);
      }
      else {
         this.callback = callback;
         this.userData = userData;
      }

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   }


   /** @return The callback handle can be null for weak references */
   I_Timeout getCallback() {
      if (this.useWeakReference) {
         WeakReference weak = (WeakReference)this.callback;
         return (I_Timeout)weak.get();
      }
      else {
         return (I_Timeout)this.callback;
      }
   }

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   Object getUserData() {
      if (this.userData == null) {
         return null;
      }
      if (this.useWeakReference) {
         WeakReference weak = (WeakReference)this.userData;
         return weak.get();
      }
      else {
         return this.userData;
      }
   }

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            this.childs = new HashMap();
         }
         if (doClone) {
            ContextNode clone = child.getClone();
            clone.parent = this;
            this.childs.put(clone.getAbsoluteName(), new WeakReference(clone));
         }
         else {
            if (child.parent != null && this != child.parent) {
               // If child had another parent already remove it
               child.parent.removeChild(child);
            }
            child.parent = this;
            this.childs.put(child.getAbsoluteName(), new WeakReference(child));
         }
      }
      return true;
   }

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                                                     Component component) {
        // ATTN: component has a strong reference to window via chain
        // of Component.parent fields.  Since WeakHasMap refers to its
        // values strongly, we need to break the strong link from the
        // value (component) back to its key (window).
        WeakReference weakValue = null;
        if (component != null) {
            weakValue = new WeakReference(component);
        }
        mostRecentFocusOwners.put(window, weakValue);
    }

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    /*
     * Please be careful changing this method! It is called from
     * javax.swing.JComponent.runInputVerifier() using reflection.
     */
    static synchronized Component getMostRecentFocusOwner(Window window) {
        WeakReference weakValue =
            (WeakReference)mostRecentFocusOwners.get(window);
        return weakValue == null ? null : (Component)weakValue.get();
    }

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    {
        if (Thread.currentThread() != dispatchThread) {
            return;
        }


        currentEvent = new WeakReference(e);


        // This series of 'instanceof' checks should be replaced with a
        // polymorphic type (for example, an interface which declares a
        // getWhen() method). However, this would require us to make such
        // a type public, or to place it in sun.awt. Both of these approaches

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      // Remove ourself from any previous parent.
      if (parent != null) {
    // assert parent.kids != null;
    for (Iterator iter = parent.kids.iterator(); iter.hasNext(); ) {
        WeakReference ref = (WeakReference) iter.next();
        Logger kid = (Logger) ref.get();
        if (kid == this) {
            iter.remove();
      break;
        }
     }
    // We have now removed ourself from our parents' kids.
      }


      // Set our new parent.
      parent = newParent;
      if (parent.kids == null) {
          parent.kids = new ArrayList(2);
      }
      parent.kids.add(new WeakReference(this));


      // As a result of the reparenting, the effective level
      // may have changed for us and our children.
      updateEffectiveLevel();

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  // System.err.println("effective level: \"" + getName() + "\" := " + level);


  // Recursively update the level on each of our kids.
  if (kids != null) {
      for (int i = 0; i < kids.size(); i++) {
          WeakReference ref = (WeakReference)kids.get(i);
    Logger kid = (Logger) ref.get();
    if (kid != null) {
        kid.updateEffectiveLevel();
     }
      }
  }

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       * otherwise, remove the reserved entry.  In all cases, notify
       * all waiters on reserved entries in this cache.
       */
      synchronized (cache) {
    if (proxyClass != null) {
        cache.put(key, new WeakReference(proxyClass));
    } else {
        cache.remove(key);
    }
    cache.notifyAll();
      }

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