001 /* AbstractUndoableEdit.java --
002 Copyright (C) 2002, 2003, 2004 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
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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.
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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
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031 independent module, the terms and conditions of the license of that
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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
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036 exception statement from your version. */
037
038
039 package javax.swing.undo;
040
041 import java.io.Serializable;
042
043 import javax.swing.UIManager;
044
045 /**
046 * A default implementation of <code>UndoableEdit</code> that can be
047 * used as a base for implementing editing operations.
048 *
049 * @author Andrew Selkirk (aselkirk@sympatico.ca)
050 * @author Sascha Brawer (brawer@dandelis.ch)
051 */
052 public class AbstractUndoableEdit
053 implements UndoableEdit, Serializable
054 {
055 /**
056 * The serialization ID. Verified using the <code>serialver</code>
057 * tool of Apple/Sun JDK 1.3.1 on MacOS X 10.1.5, and Sun JDK
058 * 1.4.1_01 on GNU/Linux.
059 */
060 static final long serialVersionUID = 580150227676302096L;
061
062
063 /**
064 * The constant string “Undo”, which was returned by
065 * {@link #getUndoPresentationName()} on early versions of the
066 * platform. However, this field has become obsolete with version
067 * 1.3.1. That method now retrieves a localized string from the
068 * {@link javax.swing.UIManager}, using the key
069 * <code>“AbstractUndoableEdit.undoText”</code>.
070 */
071 protected static final String UndoName = "Undo";
072
073
074 /**
075 * The constant string “Redo”, which was returned by
076 * {@link #getRedoPresentationName()} on early versions of the
077 * platform. However, this field has become obsolete with version
078 * 1.3.1. That method now retrieves a localized string from the
079 * {@link javax.swing.UIManager}, using the key
080 * <code>“AbstractUndoableEdit.redoText”</code>.
081 */
082 protected static final String RedoName = "Redo";
083
084
085 /**
086 * Indicates whether this editing action has been executed. A value
087 * of <code>true</code> means that the action was performed, or that
088 * a redo operation was successful. A value of <code>false</code>
089 * means that the action has not yet performed, or that an undo
090 * operation was successful.
091 */
092 private boolean hasBeenDone;
093
094
095 /**
096 * Indicates whether this editing action is still alive. The value
097 * is set to <code>true</code> by the constructor, and to
098 * <code>false</code> by the {@link #die()} method.
099 */
100 private boolean alive;
101
102
103 /**
104 * Constructs a new <code>AbstractUndoableEdit</code>. The initial
105 * state is that the editing action is alive, and
106 * <code>hasBeenDone</code> is <code>true</code>.
107 */
108 public AbstractUndoableEdit()
109 {
110 // The API specification is not clear, but Mauve test code has
111 // determined that hasBeenDone is initially set to true.
112 alive = hasBeenDone = true;
113 }
114
115
116 /**
117 * Undoes this editing action.
118 *
119 * @throws CannotUndoException if {@link #canUndo()} returns
120 * <code>false</code>, for example because this action has already
121 * been undone.
122 *
123 * @see #canUndo()
124 * @see #redo()
125 */
126 public void undo()
127 throws CannotUndoException
128 {
129 if (!canUndo())
130 throw new CannotUndoException();
131 hasBeenDone = false;
132 }
133
134
135 /**
136 * Determines whether it would be possible to undo this editing
137 * action.
138 *
139 * @return <code>true</code> to indicate that this action can be
140 * undone, <code>false</code> otherwise.
141 *
142 * @see #undo()
143 * @see #canRedo()
144 */
145 public boolean canUndo()
146 {
147 return alive && hasBeenDone;
148 }
149
150
151 /**
152 * Redoes this editing action.
153 *
154 * @throws CannotRedoException if {@link #canRedo()} returns
155 * <code>false</code>, for example because this action has not
156 * yet been undone.
157 *
158 * @see #canRedo()
159 * @see #undo()
160 */
161 public void redo()
162 throws CannotRedoException
163 {
164 if (!canRedo())
165 throw new CannotRedoException();
166 hasBeenDone = true;
167 }
168
169
170 /**
171 * Determines whether it would be possible to redo this editing
172 * action.
173 *
174 * @return <code>true</code> to indicate that this action can be
175 * redone, <code>false</code> otherwise.
176 *
177 * @see #redo()
178 * @see #canUndo()
179 */
180 public boolean canRedo()
181 {
182 return alive && !hasBeenDone;
183 }
184
185
186 /**
187 * Informs this edit action that it will no longer be used. Some
188 * actions might use this information to release resources, for
189 * example open files. Called by {@link UndoManager} before this
190 * action is removed from the edit queue.
191 */
192 public void die()
193 {
194 alive = false;
195 }
196
197
198 /**
199 * Incorporates another editing action into this one, thus forming a
200 * combined action.
201 *
202 * <p>The default implementation always returns <code>false</code>,
203 * indicating that the editing action could not be incorporated.
204 *
205 * @param edit the editing action to be incorporated.
206 */
207 public boolean addEdit(UndoableEdit edit)
208 {
209 return false;
210 }
211
212
213 /**
214 * Incorporates another editing action into this one, thus forming a
215 * combined action that replaces the argument action.
216 *
217 * <p>The default implementation always returns <code>false</code>,
218 * indicating that the argument action should not be replaced.
219 *
220 * @param edit the editing action to be replaced.
221 */
222 public boolean replaceEdit(UndoableEdit edit)
223 {
224 return false;
225 }
226
227
228 /**
229 * Determines whether this editing action is significant enough for
230 * being seperately undoable by the user. A typical significant
231 * action would be the resizing of an object. However, changing the
232 * selection in a text document would usually not be considered
233 * significant.
234 *
235 * <p>The default implementation returns <code>true</code>.
236 *
237 * @return <code>true</code> to indicate that the action is
238 * significant enough for being separately undoable, or
239 * <code>false</code> otherwise.
240 */
241 public boolean isSignificant()
242 {
243 return true;
244 }
245
246
247 /**
248 * Returns a human-readable, localized name that describes this
249 * editing action and can be displayed to the user.
250 *
251 * <p>The default implementation returns an empty string.
252 */
253 public String getPresentationName()
254 {
255 return "";
256 }
257
258
259 /**
260 * Calculates a localized name for presenting the undo action to the
261 * user.
262 *
263 * <p>The default implementation returns the concatenation of the
264 * string “Undo” and the action name, which is
265 * determined by calling {@link #getPresentationName()}.
266 *
267 * <p>The string “Undo” is retrieved from the {@link
268 * javax.swing.UIManager}, using the key
269 * <code>“AbstractUndoableEdit.undoText”</code>. This
270 * allows the text to be localized.
271 */
272 public String getUndoPresentationName()
273 {
274 String msg, pres;
275
276 msg = UIManager.getString("AbstractUndoableEdit.undoText");
277 if (msg == null)
278 msg = UndoName;
279
280 pres = getPresentationName();
281 if ((pres == null) || (pres.length() == 0))
282 return msg;
283 else
284 return msg + ' ' + pres;
285 }
286
287
288 /**
289 * Calculates a localized name for presenting the redo action to the
290 * user.
291 *
292 * <p>The default implementation returns the concatenation of the
293 * string “Redo” and the action name, which is
294 * determined by calling {@link #getPresentationName()}.
295 *
296 * <p>The string “Redo” is retrieved from the {@link
297 * javax.swing.UIManager}, using the key
298 * <code>“AbstractUndoableEdit.redoText”</code>. This
299 * allows the text to be localized.
300 */
301 public String getRedoPresentationName()
302 {
303 String msg, pres;
304
305 msg = UIManager.getString("AbstractUndoableEdit.redoText");
306 if (msg == null)
307 msg = RedoName;
308
309 pres = getPresentationName();
310 if ((pres == null) || (pres.length() == 0))
311 return msg;
312 else
313 return msg + ' ' + pres;
314 }
315
316
317 public String toString()
318 {
319 return super.toString()
320 + " hasBeenDone: " + hasBeenDone
321 + " alive: " + alive;
322 }
323 }