Java Swing Undo-Redo

Java Swing provides support for undo/redo in applications such as text editors. Bellows are main steps for the implementation:

• Instantiate UndoManager object

  	UndoManager undo_ = new UndoManager();
  

• Create UndoAction and RedoAction class

  class UndoAction extends AbstractAction
  {
  	public UndoAction()
  	{
  		super("Undo");
  		setEnabled(false);
  	}
  
  	public void actionPerformed(ActionEvent e)
  	{
  		try
  		{
  			undo_.undo();    // undo the editing
  		}
  		catch (CannotUndoException ex)
  		{
  			System.out.println("Unable to undo: " + ex);
  			ex.printStackTrace();
  		}
  		updateUndoState();
  		redoAction.updateRedoState();
  	}
  
  	protected void updateUndoState()
  	{
  		if (undo_.canUndo()) // check if undoable
  		{
  			setEnabled(true);
  			putValue(Action.NAME, undo_.getUndoPresentationName());
  		}
  		else
  		{
  			setEnabled(false);
  			putValue(Action.NAME, "Undo");
  		}
  	}
  	private final static long serialVersionUID = 5L;
  }
  
  class RedoAction extends AbstractAction
  {
  	public RedoAction()
  	{
  		super("Redo");
  		setEnabled(false);
  	}
  
  	public void actionPerformed(ActionEvent e)
  	{
  		try
  		{
  			undo_.redo();    // redo the edit
  		}
  		catch (CannotRedoException ex)
  		{
  			System.out.println("Unable to redo: " + ex);
  			ex.printStackTrace();
  		}
  		updateRedoState();
  		undoAction.updateUndoState();
  	}
  
  	protected void updateRedoState()
  	{
  		if (undo_.canRedo())     // check if redoable
  		{
  			setEnabled(true);
  			putValue(Action.NAME, undo_.getRedoPresentationName());
  		}
  		else
  		{
  			setEnabled(false);
  			putValue(Action.NAME, "Redo");
  		}
  	}
  
  	private final static long serialVersionUID = 5L;
  }
  

• Create MyUndoableEditListener class

  protected class MyUndoableEditListener implements UndoableEditListener
  {
  	public void undoableEditHappened(UndoableEditEvent e)
  	{
  		// Remember the edit and update the menus.
  		undo_.addEdit(e.getEdit());
  		undoAction.updateUndoState();
  		redoAction.updateRedoState();
  	}
  }
  

• Instantiate UndoAction and RedoAction objects, and add to menu

  	undoAction = new UndoAction();
  	menu.add(undoAction);
  
  	redoAction = new RedoAction();
  	menu.add(redoAction);
  

• Add MyUndoableEditListener and watching for undoable changes

  	AbstractDocument doc = (AbstractDocument) textPane.getStyledDocument();
  	doc.addUndoableEditListener(new MyUndoableEditListener());