Ampel

 private int zustand = 1;

  public void ampel_WindowActivated(WindowEvent evt) {
    while (true) {
      zustand++;
      if (zustand > 4) {zustand=1;}
      switch (zustand) {
        case  1:
        panelRot.setVisible(true);
        panelGelb.setVisible(false);
        panelGruen.setVisible(false);
        break;
        case  2:
        panelRot.setVisible(true);
        panelGelb.setVisible(true);
        panelGruen.setVisible(false);
        break;
        case  3:
        panelRot.setVisible(false);
        panelGelb.setVisible(false);
        panelGruen.setVisible(true);
        break;
        case  4:
        panelRot.setVisible(false);
        panelGelb.setVisible(true);
        panelGruen.setVisible(false);
        break;
      }
      try{
        Thread.sleep(400);
      }
      catch (Exception e){
      }
    }

  }