protected JButton b1;
 
    public ButtonTurnOff() 
    {
    
        b1 = new JButton("Turn Off Computer");
        b1.setActionCommand("Turn Off Computer");
		b1.addActionListener(this);
        add(b1);
    }
 
    public void actionPerformed(ActionEvent e) 
    {
        if ("Turn Off Computer".equals(e.getActionCommand())) 
        {
           System.exit(0); //  is effectively equivalent to the call Runtime.getRuntime().exit(0)
        }
       
    }