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 }