001    /* EventListenerList.java --
002       Copyright (C) 2002, 2004, 2005, 2006,  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package javax.swing.event;
039    
040    import gnu.java.lang.CPStringBuilder;
041    
042    import java.io.IOException;
043    import java.io.ObjectInputStream;
044    import java.io.ObjectOutputStream;
045    import java.io.Serializable;
046    import java.lang.reflect.Array;
047    import java.util.EventListener;
048    
049    
050    /**
051     * A utility class for keeping track of {@link EventListener}s.
052     *
053     * <p><b>Example for using this class:</b>
054     *
055     * <blockquote><pre> import java.util.EventListener;
056     * import javax.swing.event.EventListenerList;
057     *
058     * class Foo
059     * {
060     *   protected final EventListenerList listeners = new EventListenerList();
061     *   protected BarClosedEvent barClosedEvent = null;
062     *
063     *   public void addBarListener(BarListener l)
064     *   {
065     *     listeners.<a href="#add(java.lang.Class, java.util.EventListener)"
066     *               >add</a>(BarListener.class, l);
067     *   }
068     *
069     *   public void removeBarListener(BarListener l)
070     *   {
071     *     listeners.<a href="#remove(java.lang.Class, java.util.EventListener)"
072     *               >remove</a>(BarListener.class, l);
073     *   }
074     *
075     *   protected void fireBarClosedEvent()
076     *   {
077     *     Object[] l = listeners.<a href="#getListenerList()"
078     *                            >getListenerList()</a>;
079     *
080     *     for (int i = l.length - 2; i >= 0; i -= 2)
081     *       if (l[i] == BarListener.class)
082     *         {
083     *           // Create the event on demand, when it is needed the first time.
084     *           if (barClosedEvent == null)
085     *             barClosedEvent = new BarClosedEvent(this);
086     *
087     *           ((BarClosedListener) l[i + 1]).barClosed(barClosedEvent);
088     *         }
089     *   }
090     * }</pre></blockquote>
091     *
092     * @author Andrew Selkirk (aselkirk@sympatico.ca)
093     * @author Sascha Brawer (brawer@dandelis.ch)
094     */
095    public class EventListenerList
096      implements Serializable
097    {
098      /**
099       * An ID for serializing instances of this class; verified with the
100       * serialver tool of Sun J2SE 1.4.1_01.
101       */
102      static final long serialVersionUID = -5677132037850737084L;
103    
104    
105      /**
106       * An empty array that is shared by all instances of this class that
107       * have no listeners.
108       */
109      private static final Object[] NO_LISTENERS = new Object[0];
110      
111      
112      /**
113       * An array with all currently registered listeners.  The array has
114       * twice as many elements as there are listeners.  For an even
115       * integer <code>i</code>, <code>listenerList[i]</code> indicates
116       * the registered class, and <code>listenerList[i + 1]</code> is the
117       * listener.
118       */
119      protected transient Object[] listenerList = NO_LISTENERS;
120    
121      
122      /**
123       * EventListenerList constructor
124       */
125      public EventListenerList()
126      {
127        // Nothing to do here.
128      }
129    
130    
131      /**
132       * Registers a listener of a specific type.
133       *
134       * @param t the type of the listener.
135       *
136       * @param listener the listener to add, which must be an instance of
137       * <code>t</code>, or of a subclass of <code>t</code>.
138       *
139       * @throws IllegalArgumentException if <code>listener</code> is not
140       * an instance of <code>t</code> (or a subclass thereof).
141       *
142       * @throws NullPointerException if <code>t</code> is <code>null</code>.
143       */
144      public <T extends EventListener> void add(Class<T> t, T listener)
145      {
146        int oldLength;
147        Object[] newList;
148    
149        if (listener == null)
150          return;
151    
152        if (!t.isInstance(listener))
153          throw new IllegalArgumentException();
154    
155        oldLength = listenerList.length;
156        newList = new Object[oldLength + 2];
157        if (oldLength > 0)
158          System.arraycopy(listenerList, 0, newList, 0, oldLength);
159    
160        newList[oldLength] = t;
161        newList[oldLength + 1] = listener;
162        listenerList = newList;
163      }
164    
165    
166      /**
167       * Determines the number of listeners.
168       */
169      public int getListenerCount()
170      {
171        return listenerList.length / 2;
172      }
173    
174    
175      /**
176       * Determines the number of listeners of a particular class.
177       *
178       * @param t the type of listeners to be counted. In order to get
179       * counted, a subscribed listener must be exactly of class
180       * <code>t</code>. Thus, subclasses of <code>t</code> will not be
181       * counted.
182       */
183      public int getListenerCount(Class<?> t)
184      {
185        int result = 0;
186        for (int i = 0; i < listenerList.length; i += 2)
187          if (t == listenerList[i])
188            ++result;
189    
190        return result;
191      }
192    
193    
194      /**
195       * Returns an array containing a sequence of listenerType/listener pairs, one
196       * for each listener.
197       * 
198       * @return An array containing the listener types and references.
199       */
200      public Object[] getListenerList()
201      {
202        // returning the internal storage is a bad idea, but tests show that the
203        // reference implementation does this...
204        return listenerList;
205      }
206    
207    
208      /**
209       * Retrieves the currently subscribed listeners of a particular
210       * type.  For a listener to be returned, it must have been
211       * registered with exactly the type <code>c</code>; subclasses are
212       * not considered equal.
213       *
214       * <p>The returned array can always be cast to <code>c[]</code>.
215       * Since it is a newly allocated copy, the caller may arbitrarily
216       * modify the array.
217       *
218       * @param c the class which was passed to {@link #add}.
219       *
220       * @throws ClassCastException if <code>c</code> does not implement
221       * the {@link EventListener} interface.
222       *
223       * @throws NullPointerException if <code>c</code> is
224       * <code>null</code>.
225       *
226       * @return an array of <code>c</code> whose elements are the
227       * currently subscribed listeners of the specified type.  If there
228       * are no such listeners, an empty array is returned.
229       *
230       * @since 1.3
231       */
232      public <T extends EventListener> T[] getListeners(Class<T> c)
233      {
234        int count, f;
235        EventListener[] result;
236    
237        count = getListenerCount(c);
238        result = (EventListener[]) Array.newInstance(c, count);
239        f = 0;
240        for (int i = listenerList.length - 2; i >= 0; i -= 2)
241          if (listenerList[i] == c)
242            result[f++] = (EventListener) listenerList[i + 1];
243        
244        return (T[]) result;
245      }
246    
247    
248      /**
249       * Removes a listener of a specific type.
250       *
251       * @param t the type of the listener.
252       *
253       * @param listener the listener to remove, which must be an instance
254       * of <code>t</code>, or of a subclass of <code>t</code>.
255       *
256       * @throws IllegalArgumentException if <code>listener</code> is not
257       * an instance of <code>t</code> (or a subclass thereof).
258       *
259       * @throws NullPointerException if <code>t</code> is <code>null</code>.
260       */
261      public <T extends EventListener> void remove(Class<T> t, T listener)
262      {
263        Object[] oldList, newList;
264        int oldLength;
265    
266        if (listener == null)
267          return;
268    
269        if (!t.isInstance(listener))
270          throw new IllegalArgumentException();
271    
272        oldList = listenerList;
273        oldLength = oldList.length;
274        for (int i = 0; i < oldLength; i += 2)
275          if (oldList[i] == t && oldList[i + 1] == listener)
276            {
277              if (oldLength == 2)
278                newList = NO_LISTENERS;
279              else
280                {
281                  newList = new Object[oldLength - 2];
282                  if (i > 0)
283                    System.arraycopy(oldList, 0, newList, 0, i);
284                  if (i < oldLength - 2)
285                    System.arraycopy(oldList, i + 2, newList, i,
286                                     oldLength - 2 - i);
287                }
288              listenerList = newList;
289              return;
290            }
291      }
292    
293    
294      /**
295       * Returns a string representation of this object that may be useful
296       * for debugging purposes.
297       */
298      public String toString()
299      {
300        CPStringBuilder buf = new CPStringBuilder("EventListenerList: ");
301        buf.append(listenerList.length / 2);
302        buf.append(" listeners: ");
303        for (int i = 0; i < listenerList.length; i += 2)
304          {
305            buf.append(" type ");
306            buf.append(((Class) listenerList[i]).getName());
307            buf.append(" listener ");
308            buf.append(listenerList[i + 1]);
309          }
310        return buf.toString();
311      }
312    
313      /**
314       * Serializes an instance to an ObjectOutputStream.
315       *
316       * @param out the stream to serialize to
317       *
318       * @throws IOException if something goes wrong
319       */
320      private void writeObject(ObjectOutputStream out)
321        throws IOException
322      {
323        out.defaultWriteObject();
324        for (int i = 0; i < listenerList.length; i += 2)
325          {
326            Class cl = (Class) listenerList[i];
327            EventListener l = (EventListener) listenerList[i + 1];
328            if (l != null && l instanceof Serializable)
329              {
330                out.writeObject(cl.getName());
331                out.writeObject(l);
332              }
333          }
334        // Write end marker.
335        out.writeObject(null);
336      }
337    
338      /**
339       * Deserializes an instance from an ObjectInputStream.
340       *
341       * @param in the input stream
342       *
343       * @throws ClassNotFoundException if a serialized class can't be found
344       * @throws IOException if something goes wrong
345       */
346      private <T extends EventListener> void readObject(ObjectInputStream in)
347        throws ClassNotFoundException, IOException
348      {
349        listenerList = NO_LISTENERS;
350        in.defaultReadObject();
351        Object type;
352        ClassLoader cl = Thread.currentThread().getContextClassLoader();
353        while ((type = in.readObject()) != null)
354          {
355            EventListener l = (EventListener) in.readObject();
356            add(((Class<T>) Class.forName((String) type, true, cl)), (T) l);
357          }
358      }
359    }