code: public void mousePressed (MouseEvent e)
      {
          // ignore if we're not enabled
          if (!isEnabled()) {
              return;
          }
  
          // keep track of the selected button
          _selectedButton = (JLabel)e.getSource();
          // if the selected button is already selected, ignore the click
          if (_selectedButton.getBorder() == SELECTED_BORDER) {
              _selectedButton = null;
          } else {
              _selectedButton.setBorder(SELECTED_BORDER);
              _selectedButton.repaint();
          }
      }
docs: documentation inherited from interface