public void actionPerformed(ActionEvent e) {
		String actionCommand = e.getActionCommand();
		if (e.getSource() instanceof JButton) {
			if ("Add".equals(actionCommand))
				add();
			if ("Subtract".equals(actionCommand))
				subtract();
			if ("Multiply".equals(actionCommand))
				multiply();
			if ("Divide".equals(actionCommand))
				divide();
		}
	}