public void mouseEntered(MouseEvent evt)
    {
        JLabel button = (JLabel)evt.getSource();
        oldBorder = button.getBorder();
        button.setBorder(ROLLOVER_BORDER);
    }
public void mouseEntered ( MouseEvent evt ) { JLabel button = ( JLabel ) evt . getSource ( ) ; oldBorder = button . getBorder ( ) ; button . setBorder ( ROLLOVER_BORDER ) ; }
Invoked when the mouse enters a component.