JComboBoxのドロップダウンリストに角丸のBorderを設定する

JComboBox<String> combo1 = new JComboBox<String>(makeModel()) {
  private transient PopupMenuListener listener;
  @Override public void updateUI() {
    removePopupMenuListener(listener);
    UIManager.put("ComboBox.border", new RoundedCornerBorder());
    super.updateUI();
    setUI(new BasicComboBoxUI());
    listener = new HeavyWeightContainerListener();
    addPopupMenuListener(listener);
    Object o = getAccessibleContext().getAccessibleChild(0);
    if (o instanceof JComponent) {
      JComponent c = (JComponent) o;
      c.setBorder(new RoundedCornerBorder());
      c.setForeground(FOREGROUND);
      c.setBackground(BACKGROUND);
    }
  }
};