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 java.io.IOException;
041 import java.io.ObjectInputStream;
042 import java.io.ObjectOutputStream;
043 import java.io.Serializable;
044 import java.lang.reflect.Array;
045 import java.util.EventListener;
046
047
048 /**
049 * A utility class for keeping track of {@link EventListener}s.
050 *
051 * <p><b>Example for using this class:</b>
052 *
053 * <blockquote><pre> import java.util.EventListener;
054 * import javax.swing.event.EventListenerList;
055 *
056 * class Foo
057 * {
058 * protected final EventListenerList listeners = new EventListenerList();
059 * protected BarClosedEvent barClosedEvent = null;
060 *
061 * public void addBarListener(BarListener l)
062 * {
063 * listeners.<a href="#add(java.lang.Class, java.util.EventListener)"
064 * >add</a>(BarListener.class, l);
065 * }
066 *
067 * public void removeBarListener(BarListener l)
068 * {
069 * listeners.<a href="#remove(java.lang.Class, java.util.EventListener)"
070 * >remove</a>(BarListener.class, l);
071 * }
072 *
073 * protected void fireBarClosedEvent()
074 * {
075 * Object[] l = listeners.<a href="#getListenerList()"
076 * >getListenerList()</a>;
077 *
078 * for (int i = l.length - 2; i >= 0; i -= 2)
079 * if (l[i] == BarListener.class)
080 * {
081 * // Create the event on demand, when it is needed the first time.
082 * if (barClosedEvent == null)
083 * barClosedEvent = new BarClosedEvent(this);
084 *
085 * ((BarClosedListener) l[i + 1]).barClosed(barClosedEvent);
086 * }
087 * }
088 * }</pre></blockquote>
089 *
090 * @author Andrew Selkirk (aselkirk@sympatico.ca)
091 * @author Sascha Brawer (brawer@dandelis.ch)
092 */
093 public class EventListenerList
094 implements Serializable
095 {
096 /**
097 * An ID for serializing instances of this class; verified with the
098 * serialver tool of Sun J2SE 1.4.1_01.
099 */
100 static final long serialVersionUID = -5677132037850737084L;
101
102
103 /**
104 * An empty array that is shared by all instances of this class that
105 * have no listeners.
106 */
107 private static final Object[] NO_LISTENERS = new Object[0];
108
109
110 /**
111 * An array with all currently registered listeners. The array has
112 * twice as many elements as there are listeners. For an even
113 * integer <code>i</code>, <code>listenerList[i]</code> indicates
114 * the registered class, and <code>listenerList[i + 1]</code> is the
115 * listener.
116 */
117 protected transient Object[] listenerList = NO_LISTENERS;
118
119
120 /**
121 * EventListenerList constructor
122 */
123 public EventListenerList()
124 {
125 // Nothing to do here.
126 }
127
128
129 /**
130 * Registers a listener of a specific type.
131 *
132 * @param t the type of the listener.
133 *
134 * @param listener the listener to add, which must be an instance of
135 * <code>t</code>, or of a subclass of <code>t</code>.
136 *
137 * @throws IllegalArgumentException if <code>listener</code> is not
138 * an instance of <code>t</code> (or a subclass thereof).
139 *
140 * @throws NullPointerException if <code>t</code> is <code>null</code>.
141 */
142 public <T extends EventListener> void add(Class<T> t, T listener)
143 {
144 int oldLength;
145 Object[] newList;
146
147 if (listener == null)
148 return;
149
150 if (!t.isInstance(listener))
151 throw new IllegalArgumentException();
152
153 oldLength = listenerList.length;
154 newList = new Object[oldLength + 2];
155 if (oldLength > 0)
156 System.arraycopy(listenerList, 0, newList, 0, oldLength);
157
158 newList[oldLength] = t;
159 newList[oldLength + 1] = listener;
160 listenerList = newList;
161 }
162
163
164 /**
165 * Determines the number of listeners.
166 */
167 public int getListenerCount()
168 {
169 return listenerList.length / 2;
170 }
171
172
173 /**
174 * Determines the number of listeners of a particular class.
175 *
176 * @param t the type of listeners to be counted. In order to get
177 * counted, a subscribed listener must be exactly of class
178 * <code>t</code>. Thus, subclasses of <code>t</code> will not be
179 * counted.
180 */
181 public int getListenerCount(Class<?> t)
182 {
183 int result = 0;
184 for (int i = 0; i < listenerList.length; i += 2)
185 if (t == listenerList[i])
186 ++result;
187
188 return result;
189 }
190
191
192 /**
193 * Returns an array containing a sequence of listenerType/listener pairs, one
194 * for each listener.
195 *
196 * @return An array containing the listener types and references.
197 */
198 public Object[] getListenerList()
199 {
200 // returning the internal storage is a bad idea, but tests show that the
201 // reference implementation does this...
202 return listenerList;
203 }
204
205
206 /**
207 * Retrieves the currently subscribed listeners of a particular
208 * type. For a listener to be returned, it must have been
209 * registered with exactly the type <code>c</code>; subclasses are
210 * not considered equal.
211 *
212 * <p>The returned array can always be cast to <code>c[]</code>.
213 * Since it is a newly allocated copy, the caller may arbitrarily
214 * modify the array.
215 *
216 * @param c the class which was passed to {@link #add}.
217 *
218 * @throws ClassCastException if <code>c</code> does not implement
219 * the {@link EventListener} interface.
220 *
221 * @throws NullPointerException if <code>c</code> is
222 * <code>null</code>.
223 *
224 * @return an array of <code>c</code> whose elements are the
225 * currently subscribed listeners of the specified type. If there
226 * are no such listeners, an empty array is returned.
227 *
228 * @since 1.3
229 */
230 public <T extends EventListener> T[] getListeners(Class<T> c)
231 {
232 int count, f;
233 EventListener[] result;
234
235 count = getListenerCount(c);
236 result = (EventListener[]) Array.newInstance(c, count);
237 f = 0;
238 for (int i = listenerList.length - 2; i >= 0; i -= 2)
239 if (listenerList[i] == c)
240 result[f++] = (EventListener) listenerList[i + 1];
241
242 return (T[]) result;
243 }
244
245
246 /**
247 * Removes a listener of a specific type.
248 *
249 * @param t the type of the listener.
250 *
251 * @param listener the listener to remove, which must be an instance
252 * of <code>t</code>, or of a subclass of <code>t</code>.
253 *
254 * @throws IllegalArgumentException if <code>listener</code> is not
255 * an instance of <code>t</code> (or a subclass thereof).
256 *
257 * @throws NullPointerException if <code>t</code> is <code>null</code>.
258 */
259 public <T extends EventListener> void remove(Class<T> t, T listener)
260 {
261 Object[] oldList, newList;
262 int oldLength;
263
264 if (listener == null)
265 return;
266
267 if (!t.isInstance(listener))
268 throw new IllegalArgumentException();
269
270 oldList = listenerList;
271 oldLength = oldList.length;
272 for (int i = 0; i < oldLength; i += 2)
273 if (oldList[i] == t && oldList[i + 1] == listener)
274 {
275 if (oldLength == 2)
276 newList = NO_LISTENERS;
277 else
278 {
279 newList = new Object[oldLength - 2];
280 if (i > 0)
281 System.arraycopy(oldList, 0, newList, 0, i);
282 if (i < oldLength - 2)
283 System.arraycopy(oldList, i + 2, newList, i,
284 oldLength - 2 - i);
285 }
286 listenerList = newList;
287 return;
288 }
289 }
290
291
292 /**
293 * Returns a string representation of this object that may be useful
294 * for debugging purposes.
295 */
296 public String toString()
297 {
298 StringBuffer buf = new StringBuffer("EventListenerList: ");
299 buf.append(listenerList.length / 2);
300 buf.append(" listeners: ");
301 for (int i = 0; i < listenerList.length; i += 2)
302 {
303 buf.append(" type ");
304 buf.append(((Class) listenerList[i]).getName());
305 buf.append(" listener ");
306 buf.append(listenerList[i + 1]);
307 }
308 return buf.toString();
309 }
310
311 /**
312 * Serializes an instance to an ObjectOutputStream.
313 *
314 * @param out the stream to serialize to
315 *
316 * @throws IOException if something goes wrong
317 */
318 private void writeObject(ObjectOutputStream out)
319 throws IOException
320 {
321 out.defaultWriteObject();
322 for (int i = 0; i < listenerList.length; i += 2)
323 {
324 Class cl = (Class) listenerList[i];
325 EventListener l = (EventListener) listenerList[i + 1];
326 if (l != null && l instanceof Serializable)
327 {
328 out.writeObject(cl.getName());
329 out.writeObject(l);
330 }
331 }
332 // Write end marker.
333 out.writeObject(null);
334 }
335
336 /**
337 * Deserializes an instance from an ObjectInputStream.
338 *
339 * @param in the input stream
340 *
341 * @throws ClassNotFoundException if a serialized class can't be found
342 * @throws IOException if something goes wrong
343 */
344 private <T extends EventListener> void readObject(ObjectInputStream in)
345 throws ClassNotFoundException, IOException
346 {
347 listenerList = NO_LISTENERS;
348 in.defaultReadObject();
349 Object type;
350 ClassLoader cl = Thread.currentThread().getContextClassLoader();
351 while ((type = in.readObject()) != null)
352 {
353 EventListener l = (EventListener) in.readObject();
354 add(((Class<T>) Class.forName((String) type, true, cl)), (T) l);
355 }
356 }
357 }