Swing/PopupMenuTitle のバックアップ(No.1)

JPopupMenu popup1 = new JPopupMenu("JPopupMenu#setLabel(...)") {
  @Override public void updateUI() {
    setBorder(null);
    super.updateUI();
    Border border = getBorder();
    String title = getLabel();
    if (!isCompoundMotifBorderBorder(border) && title != null) {
      Color color = UIManager.getColor("Separator.foreground");
      Border underline = BorderFactory.createMatteBorder(1, 0, 0, 0, color);
      Border labelBorder = BorderFactory.createTitledBorder(
          underline,
          title,
          TitledBorder.CENTER,
          TitledBorder.ABOVE_TOP,
          getFont(),
          getForeground());
      setBorder(BorderFactory.createCompoundBorder(border, labelBorder));
    }
  }
};

private static boolean isCompoundMotifBorderBorder(Border border) {
  boolean b0 = border instanceof CompoundBorder;
  boolean b1 = b0 && isMotifBorder(((CompoundBorder) border).getInsideBorder());
  boolean b2 = b0 && isMotifBorder(((CompoundBorder) border).getOutsideBorder());
  return b1 || b2;
}

private static boolean isMotifBorder(Border border) {
  return border.getClass().getName().contains("MotifBorders");
}