static void jenableUndo(JTextComponent textcomp) {
  final new UndoManager undo;
  textcomp.getDocument().addUndoableEditListener(new UndoableEditListener() {
    public void undoableEditHappened(UndoableEditEvent evt) {
      undo.addEdit(evt.getEdit());
    }
  });
  
  textcomp.getActionMap().put("Undo", abstractAction("Undo", r {
    if (undo.canUndo()) undo.undo()
  }));
  textcomp.getInputMap().put(KeyStroke.getKeyStroke("control Z"), "Undo");
}