JTextArea textarea = new JTextArea();
 final UndoManager undo = new UndoManager();
 Document doc = textarea.getDocument();
 
 //The next two lines should be in one line.    
 doc.addUndoableEditListener(
   new UndoableEditListener() {
     The next two lines should be in one line.
     public void undoableEditHappened(
       UndoableEditEvent evt) {
         undo.addEdit(evt.getEdit());
     }
 });
 
 textarea.getActionMap().put("Undo",
     new AbstractAction("Undo") {
         public void actionPerformed(ActionEvent evt) {
             try {
                 if (undo.canUndo()) {
                     undo.undo();
                 }
             } catch (CannotUndoException e) {
             }
         }
     });
 textarea.getInputMap().put(KeyStroke.getKeyStroke(
   "control Z"), "Undo");
 
 textarea.getActionMap().put("Redo",
 new AbstractAction("Redo") {
         public void actionPerformed(ActionEvent evt) {
             try {
                 if (undo.canRedo()) {
                     undo.redo();
                 } 
             } catch (CannotRedoException e) {
             }
         }
     });
  textarea.getInputMap().put(KeyStroke.getKeyStroke(
    "control Y"), "Redo");