Source for javax.swing.undo.StateEdit

   1: /* StateEdit.java -- UndoableEdit for StateEditable implementations.
   2:    Copyright (C) 2002, 2003 Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: 
  39: package javax.swing.undo;
  40: 
  41: import java.util.Hashtable;
  42: import java.util.Iterator;
  43: 
  44: /**
  45:  * A helper class, making it easy to support undo and redo.
  46:  *
  47:  * <p>The following example shows how to use this class.</p>
  48:  *
  49:  * <pre>
  50:  * Foo foo; // class Foo implements {@link StateEditable}
  51:  * StateEdit edit;
  52:  *
  53:  * edit = new StateEdit(foo, "Name Change");
  54:  * foo.setName("Jane Doe");
  55:  * edit.end();
  56:  * undoManager.addEdit(edit);
  57:  * </pre>
  58:  *
  59:  * <p>If <code>Foo</code>&#x2019;s implementation of {@link
  60:  * StateEditable} considers the name as part of the editable state,
  61:  * the user can now choose &#x201c;Undo Name Change&#x201d; or
  62:  * &#x201c;Redo Name Change&#x201d; from the respective menu. No
  63:  * further undo support is needed from the application.</p>
  64:  *
  65:  * <p>The following explains what happens in the example.</p>
  66:  *
  67:  * <ol>
  68:  * <li>When a <code>StateEdit</code> is created, the associated
  69:  *     {@link StateEditable} gets asked to store its state into a hash
  70:  *     table, {@link #preState}.</li>
  71:  * <li>The application will now perform some changes to the edited
  72:  *     object. This typically happens by invoking methods on the edited
  73:  *     object.</li>
  74:  * <li>The editing phase is terminated by invoking the {@link #end()}
  75:  *     method of the <code>StateEdit</code>. The <code>end()</code> method
  76:  *     does two things.
  77:  *
  78:  *     <ul>
  79:  *     <li>The edited object receives a second request for storing
  80:  *         its state.  This time, it will use a different hash table, {@link
  81:  *         #postState}.</li>
  82:  *     <li>To increase efficiency, the <code>StateEdit</code> now removes
  83:  *         any entries from {@link #preState} and {@link #postState} that have
  84:  *         the same key, and whose values are equal. Equality is determined
  85:  *         by invoking the <code>equals</code> method inherited from
  86:  *         {@link java.lang.Object}.</li>
  87:  *     </ul></li>
  88:  * <li>When the user later chooses to undo the <code>StateEdit</code>,
  89:  * the edited object is asked to {@linkplain StateEditable#restoreState
  90:  * restore its state} from the {@link #preState} table.  Similarly,
  91:  * when the user chooses to <i>redo</i> the <code>StateEdit</code>,
  92:  * the edited object gets asked to restore its state from the {@link
  93:  * #postState}.</li>
  94:  * </ol>
  95:  *
  96:  * @author Andrew Selkirk (aselkirk@sympatico.ca)
  97:  * @author Sascha Brawer (brawer@dandelis.ch)
  98:  */
  99: public class StateEdit
 100:   extends AbstractUndoableEdit
 101: {
 102:   /**
 103:    * The ID of the Java source file in Sun&#x2019;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&#x2019;s reference implementation, GNU Classpath also has to
 107:    * provide this field. However, we do not try to match its value.
 108:    */
 109:   protected static final String RCSID = "";
 110: 
 111: 
 112:   /**
 113:    * The object which is being edited by this <code>StateEdit</code>.
 114:    */
 115:   protected StateEditable object;
 116: 
 117: 
 118:   /**
 119:    * The state of <code>object</code> at the time of constructing
 120:    * this <code>StateEdit</code>.
 121:    */
 122:   protected Hashtable preState;
 123: 
 124: 
 125:   /**
 126:    * The state of <code>object</code> at the time when {@link #end()}
 127:    * was called.
 128:    */
 129:   protected Hashtable postState;
 130: 
 131: 
 132:   /**
 133:    * A human-readable name for this edit action.
 134:    */
 135:   protected String undoRedoName;
 136: 
 137: 
 138:   /**
 139:    * Constructs a <code>StateEdit</code>, specifying the object whose
 140:    * state is being edited.
 141:    *
 142:    * @param obj the object whose state is being edited by this
 143:    * <code>StateEdit</code>.
 144:    */
 145:   public StateEdit(StateEditable obj)
 146:   {
 147:     init(obj, null);
 148:   }
 149: 
 150: 
 151:   /**
 152:    * Constructs a <code>StateEdit</code>, specifying the object whose
 153:    * state is being edited.
 154:    *
 155:    * @param obj the object whose state is being edited by this
 156:    * <code>StateEdit</code>.
 157:    *
 158:    * @param name the human-readable name of the editing action.
 159:    */
 160:   public StateEdit(StateEditable obj, String name)
 161:   {
 162:     init(obj, name);
 163:   }
 164: 
 165: 
 166:   /**
 167:    * Initializes this <code>StateEdit</code>. The edited object will
 168:    * be asked to store its current state into {@link #preState}.
 169:    *
 170:    * @param obj the object being edited.
 171:    *
 172:    * @param name the human-readable name of the editing action.
 173:    */
 174:   protected void init(StateEditable obj, String name)
 175:   {
 176:     object = obj;
 177:     undoRedoName = name;
 178:     preState = new Hashtable();
 179:     postState = new Hashtable();
 180:     obj.storeState(preState);
 181:   }
 182: 
 183: 
 184:   /**
 185:    * Informs this <code>StateEdit</code> that all edits are finished.
 186:    * The edited object will be asked to store its state into {@link
 187:    * #postState}, and any redundant entries will get removed from
 188:    * {@link #preState} and {@link #postState}.
 189:    */
 190:   public void end()
 191:   {
 192:     object.storeState(postState);
 193:     removeRedundantState();
 194:   }
 195: 
 196: 
 197:   /**
 198:    * Undoes this edit operation. The edited object will be asked to
 199:    * {@linkplain StateEditable#restoreState restore its state} from
 200:    * {@link #preState}.
 201:    *
 202:    * @throws CannotUndoException if {@link #canUndo()} returns
 203:    * <code>false</code>, for example because this action has already
 204:    * been undone.
 205:    */
 206:   public void undo()
 207:   {
 208:     super.undo();
 209:     object.restoreState(preState);
 210:   }
 211: 
 212: 
 213:   /**
 214:    * Redoes this edit operation. The edited object will be asked to
 215:    * {@linkplain StateEditable#restoreState restore its state} from
 216:    * {@link #postState}.
 217:    *
 218:    * @throws CannotRedoException if {@link #canRedo()} returns
 219:    * <code>false</code>, for example because this action has not yet
 220:    * been undone.
 221:    */
 222:   public void redo()
 223:   {
 224:     super.redo();
 225:     object.restoreState(postState);
 226:   }
 227: 
 228: 
 229:   /**
 230:    * Returns a human-readable, localized name that describes this
 231:    * editing action and can be displayed to the user.
 232:    *
 233:    * @return the name, or <code>null</code> if no presentation
 234:    * name is available.
 235:    */
 236:   public String getPresentationName()
 237:   {
 238:     return undoRedoName;
 239:   }
 240: 
 241: 
 242:   /**
 243:    * Removes all redundant entries from the pre- and post-edit state
 244:    * hash tables. An entry is considered redundant if it is present
 245:    * both before and after the edit, and if the two values are equal.
 246:    */
 247:   protected void removeRedundantState()
 248:   {
 249:     Iterator i = preState.keySet().iterator();
 250:     while (i.hasNext())
 251:       {
 252:     Object key = i.next();
 253:     if (postState.containsKey(key))
 254:       {
 255:         if (preState.get(key).equals(postState.get(key)))
 256:           {
 257:         i.remove();
 258:         postState.remove(key);
 259:           }
 260:       }
 261:       }
 262:   }
 263: }