Swing/ComboBoxFocusBorder のバックアップ(No.1)

JComboBox<String> combo3 = new JComboBox<String>(model) {
  @Override public void updateUI() {
    setRenderer(null);
    super.updateUI();
    if (isWindowsLnF()) {
      setRenderer(new DefaultListCellRenderer() {
        @Override public Component getListCellRendererComponent(
            JList<?> list, Object value, int index,
            boolean isSelected, boolean cellHasFocus) {
          JLabel l = (JLabel) super.getListCellRendererComponent(
              list, value, index, isSelected, cellHasFocus);
          if (index < 0) {
            l.setBorder(BorderFactory.createEmptyBorder(1, 1, 1, 1));
          }
          return l;
        }
      });
    }
  }
  @Override protected void paintBorder(Graphics g) {
    super.paintBorder(g);
    if (isFocusOwner() && !isPopupVisible() && isWindowsLnF()) {
      Graphics2D g2 = (Graphics2D) g.create();
      g2.setPaint(Color.DARK_GRAY);
      g2.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
      g2.dispose();
    }
  }
  private boolean isWindowsLnF() {
    return getUI().getClass().getName().contains("WindowsComboBoxUI");
  }
};