001/* UndoableEditSupport.java --
002   Copyright (C) 2002, 2003, 2004, 2005, 2006,  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package javax.swing.undo;
040
041import java.util.Iterator;
042import java.util.Vector;
043
044import javax.swing.event.UndoableEditEvent;
045import javax.swing.event.UndoableEditListener;
046
047/**
048 * A helper class for supporting {@link
049 * javax.swing.event.UndoableEditListener}.
050 *
051 * @author Andrew Selkirk (aselkirk@sympatico.ca)
052 * @author Sascha Brawer (brawer@dandelis.ch)
053 */
054public class UndoableEditSupport
055{
056  /**
057   * The number of times that {@link #beginUpdate()} has been called
058   * without a matching call to {@link #endUpdate()}.
059   */
060  protected int updateLevel;
061
062
063  /**
064   * compoundEdit
065   */
066  protected CompoundEdit compoundEdit;
067
068
069  /**
070   * The currently registered listeners.
071   */
072  protected Vector<UndoableEditListener> listeners =
073    new Vector<UndoableEditListener>();
074
075
076  /**
077   * The source of the broadcast UndoableEditEvents.
078   */
079  protected Object realSource;
080
081
082  /**
083   * Constructs a new helper for broadcasting UndoableEditEvents.  The
084   * events will indicate the newly constructed
085   * <code>UndoableEditSupport</code> instance as their source.
086   *
087   * @see #UndoableEditSupport(java.lang.Object)
088   */
089  public UndoableEditSupport()
090  {
091    realSource = this;
092  }
093
094
095  /**
096   * Constructs a new helper for broadcasting UndoableEditEvents.
097   *
098   * @param realSource the source of the UndoableEditEvents that will
099   * be broadcast by this helper. If <code>realSource</code> is
100   * <code>null</code>, the events will indicate the newly constructed
101   * <code>UndoableEditSupport</code> instance as their source.
102   */
103  public UndoableEditSupport(Object realSource)
104  {
105    if (realSource == null)
106      realSource = this;
107    this.realSource = realSource;
108  }
109
110
111  /**
112   * Returns a string representation of this object that may be useful
113   * for debugging.
114   */
115  public String toString()
116  {
117    // Note that often, this.realSource == this. Therefore, dumping
118    // realSource without additional checks may lead to infinite
119    // recursion. See Classpath bug #7119.
120    return super.toString() + " updateLevel: " + updateLevel
121      + " listeners: " + listeners + " compoundEdit: " + compoundEdit;
122  }
123
124
125  /**
126   * Registers a listener.
127   *
128   * @param val the listener to be added.
129   */
130  public synchronized void addUndoableEditListener(UndoableEditListener val)
131  {
132    listeners.add(val);
133  }
134
135
136  /**
137   * Unregisters a listener.
138   * @param val the listener to be removed.
139   */
140  public synchronized void removeUndoableEditListener(UndoableEditListener val)
141  {
142    listeners.removeElement(val);
143  }
144
145
146  /**
147   * Returns an array containing the currently registered listeners.
148   */
149  public synchronized UndoableEditListener[] getUndoableEditListeners()
150  {
151    UndoableEditListener[] result = new UndoableEditListener[listeners.size()];
152    return listeners.toArray(result);
153  }
154
155
156  /**
157   * Notifies all registered listeners that an {@link
158   * UndoableEditEvent} has occured.
159   *
160   * <p><b>Lack of Thread Safety:</b> It is <em>not</em> safe to call
161   * this method from concurrent threads, unless the call is protected
162   * by a synchronization on this <code>UndoableEditSupport</code>
163   * instance.
164   *
165   * @param edit the edit action to be posted.
166   */
167  protected void _postEdit(UndoableEdit edit)
168  {
169    UndoableEditEvent event;
170    Iterator<UndoableEditListener> iter;
171
172    // Do nothing if we have no listeners.
173    if (listeners.isEmpty())
174      return;
175
176    event = new UndoableEditEvent(realSource, edit);
177
178    // We clone the vector because this allows listeners to register
179    // or unregister listeners in their undoableEditHappened method.
180    // Otherwise, this would throw exceptions (in the case of
181    // Iterator, a java.util.ConcurrentModificationException; in the
182    // case of a direct loop over the Vector elements, some
183    // index-out-of-bounds exception).
184    iter = new Vector<UndoableEditListener>(listeners).iterator();
185    while (iter.hasNext())
186      iter.next().undoableEditHappened(event);
187  }
188
189
190  /**
191   * If {@link #beginUpdate} has been called (so that the current
192   * update level is greater than zero), adds the specified edit
193   * to {@link #compoundEdit}. Otherwise, notify listeners of the
194   * edit by calling {@link #_postEdit(UndoableEdit)}.
195   *
196   * <p><b>Thread Safety:</b> It is safe to call this method from any
197   * thread without external synchronization.
198   *
199   * @param edit the edit action to be posted.
200   */
201  public synchronized void postEdit(UndoableEdit edit)
202  {
203    if (compoundEdit != null)
204      compoundEdit.addEdit(edit);
205    else
206      _postEdit(edit);
207  }
208
209
210  /**
211   * Returns the current update level.
212   */
213  public int getUpdateLevel()
214  {
215    return updateLevel;
216  }
217
218
219  /**
220   * Starts a (possibly nested) update session. If the current update
221   * level is zero, {@link #compoundEdit} is set to the result of the
222   * {@link #createCompoundEdit} method. In any case, the update level
223   * is increased by one.
224   *
225   * <p><b>Thread Safety:</b> It is safe to call this method from any
226   * thread without external synchronization.
227   */
228  public synchronized void beginUpdate()
229  {
230    if (compoundEdit == null)
231      compoundEdit = createCompoundEdit();
232    ++updateLevel;
233  }
234
235
236  /**
237   * Creates a new instance of {@link CompoundEdit}. Called by {@link
238   * #beginUpdate}. If a subclass wants {@link #beginUpdate} to work
239   * on a specific {@link #compoundEdit}, it should override this
240   * method.
241   *
242   * @return a newly created instance of {@link CompoundEdit}.
243   */
244  protected CompoundEdit createCompoundEdit()
245  {
246    return new CompoundEdit();
247  }
248
249
250  /**
251   * Ends an update session. If the terminated session was the
252   * outermost session, {@link #compoundEdit} will receive an
253   * <code>end</code> message, and {@link #_postEdit} gets called in
254   * order to notify any listeners. Finally, the
255   * <code>compoundEdit</code> is discarded.
256   *
257   * <p><b>Thread Safety:</b> It is safe to call this method from any
258   * thread without external synchronization.
259   */
260  public synchronized void endUpdate()
261  {
262    if (updateLevel == 0)
263      throw new IllegalStateException();
264
265    if (--updateLevel > 0)
266      return;
267
268    compoundEdit.end();
269    _postEdit(compoundEdit);
270    compoundEdit = null;
271  }
272}