comboBox.setOpaque(true); comboBox.setLayout(createLayoutManager());
  public void installUI(JComponent c)  {    super.installUI(c);    if (c instanceof JComboBox)      {	comboBox = (JComboBox) c;	comboBox.setOpaque(true);	comboBox.setLayout(createLayoutManager());	installDefaults();	installComponents();	installListeners();	installKeyboardActions();      }  }