001 /* StateEdit.java -- UndoableEdit for StateEditable implementations. 002 Copyright (C) 2002, 2003 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.Hashtable; 042 import java.util.Iterator; 043 044 /** 045 * A helper class, making it easy to support undo and redo. 046 * 047 * <p>The following example shows how to use this class.</p> 048 * 049 * <pre> 050 * Foo foo; // class Foo implements {@link StateEditable} 051 * StateEdit edit; 052 * 053 * edit = new StateEdit(foo, "Name Change"); 054 * foo.setName("Jane Doe"); 055 * edit.end(); 056 * undoManager.addEdit(edit); 057 * </pre> 058 * 059 * <p>If <code>Foo</code>’s implementation of {@link 060 * StateEditable} considers the name as part of the editable state, 061 * the user can now choose “Undo Name Change” or 062 * “Redo Name Change” from the respective menu. No 063 * further undo support is needed from the application.</p> 064 * 065 * <p>The following explains what happens in the example.</p> 066 * 067 * <ol> 068 * <li>When a <code>StateEdit</code> is created, the associated 069 * {@link StateEditable} gets asked to store its state into a hash 070 * table, {@link #preState}.</li> 071 * <li>The application will now perform some changes to the edited 072 * object. This typically happens by invoking methods on the edited 073 * object.</li> 074 * <li>The editing phase is terminated by invoking the {@link #end()} 075 * method of the <code>StateEdit</code>. The <code>end()</code> method 076 * does two things. 077 * 078 * <ul> 079 * <li>The edited object receives a second request for storing 080 * its state. This time, it will use a different hash table, {@link 081 * #postState}.</li> 082 * <li>To increase efficiency, the <code>StateEdit</code> now removes 083 * any entries from {@link #preState} and {@link #postState} that have 084 * the same key, and whose values are equal. Equality is determined 085 * by invoking the <code>equals</code> method inherited from 086 * {@link java.lang.Object}.</li> 087 * </ul></li> 088 * <li>When the user later chooses to undo the <code>StateEdit</code>, 089 * the edited object is asked to {@linkplain StateEditable#restoreState 090 * restore its state} from the {@link #preState} table. Similarly, 091 * when the user chooses to <i>redo</i> the <code>StateEdit</code>, 092 * the edited object gets asked to restore its state from the {@link 093 * #postState}.</li> 094 * </ol> 095 * 096 * @author Andrew Selkirk (aselkirk@sympatico.ca) 097 * @author Sascha Brawer (brawer@dandelis.ch) 098 */ 099 public class StateEdit 100 extends AbstractUndoableEdit 101 { 102 /** 103 * The ID of the Java source file in Sun’s Revision Control 104 * System (RCS). This certainly should not be part of the API 105 * specification. But in order to be API-compatible with 106 * Sun’s reference implementation, GNU Classpath also has to 107 * provide this field and match its value. The value used here has 108 * been in every JDK release at least from 1.2 to 1.5. 109 */ 110 protected static final String RCSID = "$" + 111 "Id: StateEdit.java,v 1.6 1997/10/01 20:05:51 sandipc Exp $"; 112 113 114 /** 115 * The object which is being edited by this <code>StateEdit</code>. 116 */ 117 protected StateEditable object; 118 119 120 /** 121 * The state of <code>object</code> at the time of constructing 122 * this <code>StateEdit</code>. 123 */ 124 protected Hashtable<Object, Object> preState; 125 126 127 /** 128 * The state of <code>object</code> at the time when {@link #end()} 129 * was called. 130 */ 131 protected Hashtable<Object, Object> postState; 132 133 134 /** 135 * A human-readable name for this edit action. 136 */ 137 protected String undoRedoName; 138 139 140 /** 141 * Constructs a <code>StateEdit</code>, specifying the object whose 142 * state is being edited. 143 * 144 * @param obj the object whose state is being edited by this 145 * <code>StateEdit</code>. 146 */ 147 public StateEdit(StateEditable obj) 148 { 149 init(obj, null); 150 } 151 152 153 /** 154 * Constructs a <code>StateEdit</code>, specifying the object whose 155 * state is being edited. 156 * 157 * @param obj the object whose state is being edited by this 158 * <code>StateEdit</code>. 159 * 160 * @param name the human-readable name of the editing action. 161 */ 162 public StateEdit(StateEditable obj, String name) 163 { 164 init(obj, name); 165 } 166 167 168 /** 169 * Initializes this <code>StateEdit</code>. The edited object will 170 * be asked to store its current state into {@link #preState}. 171 * 172 * @param obj the object being edited. 173 * 174 * @param name the human-readable name of the editing action. 175 */ 176 protected void init(StateEditable obj, String name) 177 { 178 object = obj; 179 undoRedoName = name; 180 preState = new Hashtable<Object,Object>(); 181 postState = new Hashtable<Object,Object>(); 182 obj.storeState(preState); 183 } 184 185 186 /** 187 * Informs this <code>StateEdit</code> that all edits are finished. 188 * The edited object will be asked to store its state into {@link 189 * #postState}, and any redundant entries will get removed from 190 * {@link #preState} and {@link #postState}. 191 */ 192 public void end() 193 { 194 object.storeState(postState); 195 removeRedundantState(); 196 } 197 198 199 /** 200 * Undoes this edit operation. The edited object will be asked to 201 * {@linkplain StateEditable#restoreState restore its state} from 202 * {@link #preState}. 203 * 204 * @throws CannotUndoException if {@link #canUndo()} returns 205 * <code>false</code>, for example because this action has already 206 * been undone. 207 */ 208 public void undo() 209 { 210 super.undo(); 211 object.restoreState(preState); 212 } 213 214 215 /** 216 * Redoes this edit operation. The edited object will be asked to 217 * {@linkplain StateEditable#restoreState restore its state} from 218 * {@link #postState}. 219 * 220 * @throws CannotRedoException if {@link #canRedo()} returns 221 * <code>false</code>, for example because this action has not yet 222 * been undone. 223 */ 224 public void redo() 225 { 226 super.redo(); 227 object.restoreState(postState); 228 } 229 230 231 /** 232 * Returns a human-readable, localized name that describes this 233 * editing action and can be displayed to the user. 234 * 235 * @return the name, or <code>null</code> if no presentation 236 * name is available. 237 */ 238 public String getPresentationName() 239 { 240 return undoRedoName; 241 } 242 243 244 /** 245 * Removes all redundant entries from the pre- and post-edit state 246 * hash tables. An entry is considered redundant if it is present 247 * both before and after the edit, and if the two values are equal. 248 */ 249 protected void removeRedundantState() 250 { 251 Iterator i = preState.keySet().iterator(); 252 while (i.hasNext()) 253 { 254 Object key = i.next(); 255 if (postState.containsKey(key)) 256 { 257 if (preState.get(key).equals(postState.get(key))) 258 { 259 i.remove(); 260 postState.remove(key); 261 } 262 } 263 } 264 } 265 }