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+/* AbstractUndoableEdit.java --
+   Copyright (C) 2002, 2003, 2004  Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package javax.swing.undo;
+
+import java.io.Serializable;
+
+import javax.swing.UIManager;
+
+/**
+ * A default implementation of <code>UndoableEdit</code> that can be
+ * used as a base for implementing editing operations.
+ *
+ * @author Andrew Selkirk (aselkirk@sympatico.ca)
+ * @author Sascha Brawer (brawer@dandelis.ch)
+ */
+public class AbstractUndoableEdit
+  implements UndoableEdit, Serializable
+{
+  /**
+   * The serialization ID.  Verified using the <code>serialver</code>
+   * tool of Apple/Sun JDK 1.3.1 on MacOS X 10.1.5, and Sun JDK
+   * 1.4.1_01 on GNU/Linux.
+   */
+  static final long serialVersionUID = 580150227676302096L;
+
+
+  /**
+   * The constant string &#x201c;Undo&#x201d;, which was returned by
+   * {@link #getUndoPresentationName()} on early versions of the
+   * platform. However, this field has become obsolete with version
+   * 1.3.1.  That method now retrieves a localized string from the
+   * {@link javax.swing.UIManager}, using the key
+   * <code>&#x201c;AbstractUndoableEdit.undoText&#x201d;</code>.
+   */
+  protected static final String UndoName = "Undo";
+
+
+  /**
+   * The constant string &#x201c;Redo&#x201d;, which was returned by
+   * {@link #getRedoPresentationName()} on early versions of the
+   * platform. However, this field has become obsolete with version
+   * 1.3.1.  That method now retrieves a localized string from the
+   * {@link javax.swing.UIManager}, using the key
+   * <code>&#x201c;AbstractUndoableEdit.redoText&#x201d;</code>.
+   */
+  protected static final String RedoName = "Redo";
+
+
+  /**
+   * Indicates whether this editing action has been executed.  A value
+   * of <code>true</code> means that the action was performed, or that
+   * a redo operation was successful. A value of <code>false</code>
+   * means that the action has not yet performed, or that an undo
+   * operation was successful.
+   */
+  private boolean hasBeenDone;
+
+
+  /**
+   * Indicates whether this editing action is still alive. The value
+   * is set to <code>true</code> by the constructor, and to
+   * <code>false</code> by the {@link #die()} method.
+   */
+  private boolean alive;
+
+
+  /**
+   * Constructs a new <code>AbstractUndoableEdit</code>. The initial
+   * state is that the editing action is alive, and
+   * <code>hasBeenDone</code> is <code>true</code>.
+   */
+  public AbstractUndoableEdit()
+  {
+    // The API specification is not clear, but Mauve test code has
+    // determined that hasBeenDone is initially set to true.
+    alive = hasBeenDone = true;
+  }
+
+
+  /**
+   * Undoes this editing action.
+   *
+   * @throws CannotUndoException if {@link #canUndo()} returns
+   * <code>false</code>, for example because this action has already
+   * been undone.
+   *
+   * @see #canUndo()
+   * @see #redo()
+   */
+  public void undo()
+    throws CannotUndoException
+  {
+    if (!canUndo())
+      throw new CannotUndoException();
+    hasBeenDone = false;
+  }
+  
+  
+  /**
+   * Determines whether it would be possible to undo this editing
+   * action.
+   *
+   * @return <code>true</code> to indicate that this action can be
+   * undone, <code>false</code> otherwise.
+   *
+   * @see #undo()
+   * @see #canRedo()
+   */
+  public boolean canUndo()
+  {
+    return alive && hasBeenDone;
+  }
+  
+  
+  /**
+   * Redoes this editing action.
+   *
+   * @throws CannotRedoException if {@link #canRedo()} returns
+   * <code>false</code>, for example because this action has not
+   * yet been undone.
+   *
+   * @see #canRedo()
+   * @see #undo()
+   */
+  public void redo()
+    throws CannotRedoException
+  {
+    if (!canRedo())
+      throw new CannotRedoException();
+    hasBeenDone = true;
+  }
+  
+  
+  /**
+   * Determines whether it would be possible to redo this editing
+   * action.
+   *
+   * @return <code>true</code> to indicate that this action can be
+   * redone, <code>false</code> otherwise.
+   *
+   * @see #redo()
+   * @see #canUndo()
+   */
+  public boolean canRedo()
+  {
+    return alive && !hasBeenDone;
+  }
+
+
+  /**
+   * Informs this edit action that it will no longer be used. Some
+   * actions might use this information to release resources, for
+   * example open files.  Called by {@link UndoManager} before this
+   * action is removed from the edit queue.
+   */
+  public void die()
+  {
+    alive = false;
+  }
+
+
+  /**
+   * Incorporates another editing action into this one, thus forming a
+   * combined action.
+   *
+   * <p>The default implementation always returns <code>false</code>,
+   * indicating that the editing action could not be incorporated.
+   *
+   * @param edit the editing action to be incorporated.
+   */
+  public boolean addEdit(UndoableEdit edit)
+  {
+    return false;
+  }
+  
+  
+  /**
+   * Incorporates another editing action into this one, thus forming a
+   * combined action that replaces the argument action.
+   *
+   * <p>The default implementation always returns <code>false</code>,
+   * indicating that the argument action should not be replaced.
+   *
+   * @param edit the editing action to be replaced.
+   */
+  public boolean replaceEdit(UndoableEdit edit)
+  {
+    return false;
+  }
+  
+  
+  /**
+   * Determines whether this editing action is significant enough for
+   * being seperately undoable by the user. A typical significant
+   * action would be the resizing of an object. However, changing the
+   * selection in a text document would usually not be considered
+   * significant.
+   *
+   * <p>The default implementation returns <code>true</code>.
+   *
+   * @return <code>true</code> to indicate that the action is
+   * significant enough for being separately undoable, or
+   * <code>false</code> otherwise.
+   */
+  public boolean isSignificant()
+  {
+    return true;
+  }
+  
+  
+  /**
+   * Returns a human-readable, localized name that describes this
+   * editing action and can be displayed to the user.
+   *
+   * <p>The default implementation returns an empty string.
+   */
+  public String getPresentationName()
+  {
+    return "";
+  }
+
+
+  /**
+   * Calculates a localized name for presenting the undo action to the
+   * user.
+   *
+   * <p>The default implementation returns the concatenation of the
+   * string &#x201c;Undo&#x201d; and the action name, which is
+   * determined by calling {@link #getPresentationName()}.
+   *
+   * <p>The string &#x201c;Undo&#x201d; is retrieved from the {@link
+   * javax.swing.UIManager}, using the key
+   * <code>&#x201c;AbstractUndoableEdit.undoText&#x201d;</code>.  This
+   * allows the text to be localized.
+   */
+  public String getUndoPresentationName()
+  {
+    String msg, pres;
+
+    msg = UIManager.getString("AbstractUndoableEdit.undoText");
+    if (msg == null)
+      msg = UndoName;
+
+    pres = getPresentationName();
+    if ((pres == null) || (pres.length() == 0))
+      return msg;
+    else
+      return msg + ' ' + pres;
+  }
+
+
+  /**
+   * Calculates a localized name for presenting the redo action to the
+   * user.
+   *
+   * <p>The default implementation returns the concatenation of the
+   * string &#x201c;Redo&#x201d; and the action name, which is
+   * determined by calling {@link #getPresentationName()}.
+   *
+   * <p>The string &#x201c;Redo&#x201d; is retrieved from the {@link
+   * javax.swing.UIManager}, using the key
+   * <code>&#x201c;AbstractUndoableEdit.redoText&#x201d;</code>.  This
+   * allows the text to be localized.
+   */
+  public String getRedoPresentationName()
+  {
+    String msg, pres;
+
+    msg = UIManager.getString("AbstractUndoableEdit.redoText");
+    if (msg == null)
+      msg = RedoName;
+
+    pres = getPresentationName();
+    if ((pres == null) || (pres.length() == 0))
+      return msg;
+    else
+      return msg + ' ' + pres;
+  }
+
+
+  public String toString()
+  {
+    return super.toString()
+      + " hasBeenDone: " + hasBeenDone
+      + " alive: " + alive;
+  }
+}