libjava/java/beans/PropertyChangeListenerProxy.java

   1 /* PropertyChangeListenerProxy.java -- adds a name to a property listener
   2    Copyright (C) 2002, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.beans;
  40
  41 import java.util.EventListenerProxy;
  42
  43 /**
  44  * This class provides an extension to <code>PropertyChangeListener</code> -
  45  * associating a name with the listener. This can be used to filter the
  46  * changes that one is interested in.
  47  *
  48  * @author Eric Blake (ebb9@email.byu.edu)
  49  * @since 1.4
  50  * @status udpated to 1.4
  51  */
  52 public class PropertyChangeListenerProxy extends EventListenerProxy
  53   implements PropertyChangeListener
  54 {
  55   /**
  56    * The name of the property to listen for. Package visible for use by
  57    * PropertyChangeSupport.
  58    */
  59   final String propertyName;
  60
  61   /**
  62    * Create a new proxy which filters property change events and only passes
  63    * changes to the named property on to the delegate. A null propertyName
  64    * or listener does not fail now, but may cause a NullPointerException down
  65    * the road.
  66    *
  67    * @param propertyName the property's name to filter on
  68    * @param listener the delegate listener
  69    */
  70   public PropertyChangeListenerProxy(String propertyName,
  71                                      PropertyChangeListener listener)
  72   {
  73     super(listener);
  74     this.propertyName = propertyName;
  75   }
  76
  77   /**
  78    * Forwards the event on to the delegate if the property name matches.
  79    *
  80    * @param event the event to pass on, if it meets the filter
  81    * @throws NullPointerException if the delegate this was created with is null
  82    */
  83   public void propertyChange(PropertyChangeEvent event)
  84   {
  85     // Note: Sun does not filter, under the assumption that since
  86     // PropertyChangeSupport unwraps proxys, this method should never be
  87     // called by normal use of listeners.
  88     String name = event == null ? null : event.getPropertyName();
  89     if (name == null ? propertyName == null : name.equals(propertyName))
  90       ((PropertyChangeListener) getListener()).propertyChange(event);
  91   }
  92
  93   /**
  94    * Gets the name of the property this proxy is filtering on.
  95    *
  96    * @return the property name
  97    */
  98   public String getPropertyName()
  99   {
 100     return propertyName;
 101   }
 102 } // class PropertyChangeListenerProxy