@Override
			public void actionPerformed(ActionEvent e) {

				//it means there is nothing to undo 
				//warn user in case of user wants to make undo operation
				if(model.getObjects().size()==0 || model.getDraw_index()==0){
					JOptionPane.showMessageDialog(null,"You can't do undo operation");
				}
				else{ //tell controller to start undo operation
					paint_panel.clear();  //clear current graph
					control.unDoShape(paint_panel.getG2());					
				}
			}