shadow = null; darkShadow = null; highlight = null;
buttonBackground = null; buttonShadow = null; buttonDarkShadow = null; buttonHighlight = null;
  protected void uninstallDefaults()  {    if (comboBox.getFont() instanceof UIResource)      comboBox.setFont(null);    if (comboBox.getForeground() instanceof UIResource)      comboBox.setForeground(null);        if (comboBox.getBackground() instanceof UIResource)      comboBox.setBackground(null);    shadow = null;    darkShadow = null;    highlight = null;  }