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    1   /*
    2    * Copyright (c) 1999, 2006, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   package javax.swing;
   26   
   27   import java.beans.PropertyChangeEvent;
   28   import java.beans.PropertyChangeListener;
   29   import java.io;
   30   import java.lang.ref.WeakReference;
   31   import java.lang.ref.ReferenceQueue;
   32   
   33   /**
   34    * A package-private PropertyChangeListener which listens for
   35    * property changes on an Action and updates the properties
   36    * of an ActionEvent source.
   37    * <p>
   38    * Subclasses must override the actionPropertyChanged method,
   39    * which is invoked from the propertyChange method as long as
   40    * the target is still valid.
   41    * </p>
   42    * <p>
   43    * WARNING WARNING WARNING WARNING WARNING WARNING:<br>
   44    * Do NOT create an annonymous inner class that extends this!  If you do
   45    * a strong reference will be held to the containing class, which in most
   46    * cases defeats the purpose of this class.
   47    *
   48    * @param T the type of JComponent the underlying Action is attached to
   49    *
   50    * @author Georges Saab
   51    * @see AbstractButton
   52    */
   53   abstract class ActionPropertyChangeListener<T extends JComponent>
   54           implements PropertyChangeListener, Serializable {
   55       private static ReferenceQueue<JComponent> queue;
   56   
   57       // WeakReference's aren't serializable.
   58       private transient OwnedWeakReference<T> target;
   59       // The Component's that reference an Action do so through a strong
   60       // reference, so that there is no need to check for serialized.
   61       private Action action;
   62   
   63       private static ReferenceQueue<JComponent> getQueue() {
   64           synchronized(ActionPropertyChangeListener.class) {
   65               if (queue == null) {
   66                   queue = new ReferenceQueue<JComponent>();
   67               }
   68           }
   69           return queue;
   70       }
   71   
   72       public ActionPropertyChangeListener(T c, Action a) {
   73           super();
   74           setTarget(c);
   75           this.action = a;
   76       }
   77   
   78       /**
   79        * PropertyChangeListener method.  If the target has been gc'ed this
   80        * will remove the <code>PropertyChangeListener</code> from the Action,
   81        * otherwise this will invoke actionPropertyChanged.
   82        */
   83       public final void propertyChange(PropertyChangeEvent e) {
   84           T target = getTarget();
   85           if (target == null) {
   86               getAction().removePropertyChangeListener(this);
   87           } else {
   88               actionPropertyChanged(target, getAction(), e);
   89           }
   90       }
   91   
   92       /**
   93        * Invoked when a property changes on the Action and the target
   94        * still exists.
   95        */
   96       protected abstract void actionPropertyChanged(T target, Action action,
   97                                                     PropertyChangeEvent e);
   98   
   99       private void setTarget(T c) {
  100           ReferenceQueue<JComponent> queue = getQueue();
  101           // Check to see whether any old buttons have
  102           // been enqueued for GC.  If so, look up their
  103           // PCL instance and remove it from its Action.
  104           OwnedWeakReference r;
  105           while ((r = (OwnedWeakReference)queue.poll()) != null) {
  106               ActionPropertyChangeListener oldPCL = r.getOwner();
  107               Action oldAction = oldPCL.getAction();
  108               if (oldAction!=null) {
  109                   oldAction.removePropertyChangeListener(oldPCL);
  110               }
  111           }
  112           this.target = new OwnedWeakReference<T>(c, queue, this);
  113       }
  114   
  115       public T getTarget() {
  116           if (target == null) {
  117               // Will only happen if serialized and real target was null
  118               return null;
  119           }
  120           return this.target.get();
  121       }
  122   
  123       public Action getAction() {
  124             return action;
  125       }
  126   
  127       private void writeObject(ObjectOutputStream s) throws IOException {
  128           s.defaultWriteObject();
  129           s.writeObject(getTarget());
  130       }
  131   
  132       @SuppressWarnings("unchecked")
  133       private void readObject(ObjectInputStream s)
  134                        throws IOException, ClassNotFoundException {
  135           s.defaultReadObject();
  136           T target = (T)s.readObject();
  137           if (target != null) {
  138               setTarget(target);
  139           }
  140       }
  141   
  142   
  143       private static class OwnedWeakReference<U extends JComponent> extends
  144                                 WeakReference<U> {
  145           private ActionPropertyChangeListener owner;
  146   
  147           OwnedWeakReference(U target, ReferenceQueue<? super U> queue,
  148                              ActionPropertyChangeListener owner) {
  149               super(target, queue);
  150               this.owner = owner;
  151           }
  152   
  153           public ActionPropertyChangeListener getOwner() {
  154               return owner;
  155           }
  156       }
  157   }

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