public void redo(){
  if (!redoStack.isEmpty()) {
    UndoableAction redoEvent=redoStack.pop();
    redoEvent.redo();
    undoStack.push(redoEvent);
  }
}

public void redo ( ) { if ( ! redoStack . isEmpty ( ) ) { UndoableAction redoEvent = redoStack . pop ( ) ; redoEvent . redo ( ) ; undoStack . push ( redoEvent ) ; } }
redo the last undone action .
