swing/undo/AbstractUndoableEdit.java

/* AbstractUndoableEdit.java
   Copyright (C) 2002, 2003 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
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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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;
  }
}