001    /* UndoableEditSupport.java --
002       Copyright (C) 2002, 2003, 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    
039    package javax.swing.undo;
040    
041    import java.util.Iterator;
042    import java.util.Vector;
043    
044    import javax.swing.event.UndoableEditEvent;
045    import 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     */
054    public 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 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 = ((Vector) listeners.clone()).iterator();
185        while (iter.hasNext())
186          ((UndoableEditListener) 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    }