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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

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GNU Classpath is distributed in the hope that it will be useful, but

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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

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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

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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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this exception to your version of the library, but you are not

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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 “Undo”, 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 “Redo”, 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 “Undo” 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 “Redo” 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;

  }

}