code: public static synchronized void setToggling (AbstractButton b)
      {
          if (_toggler == null) {
              _toggler = new ActionListener () {
                  public void actionPerformed (ActionEvent event)
                  {
                      AbstractButton but = (AbstractButton) event.getSource();
                      but.setSelected(!but.isSelected());
                  }
              };
          }
  
          b.addActionListener(_toggler);
      }
docs: Set the specified button such that it alternates between being selected and not whenever it
  is pushed.