JToggleButton内に選択状態を同期したJRadioButtonを描画する

private static Component makeRadioIconLayer(AbstractButton button) {
  JRadioButton radio = new JRadioButton();
  radio.setOpaque(false);
  Dimension d = radio.getPreferredSize();
  Insets i = button.getInsets();
  button.setMargin(new Insets(i.top, d.width, i.bottom, i.right));
  button.setPreferredSize(button.getPreferredSize());
  button.setVerticalAlignment(SwingConstants.TOP);
  LayerUI<AbstractButton> layer = new LayerUI<AbstractButton>() {
    @Override public void paint(Graphics g, JComponent c) {
      super.paint(g, c);
      if (c instanceof JLayer) {
        AbstractButton b = (AbstractButton) ((JLayer<?>) c).getView();
        Graphics2D g2 = (Graphics2D) g.create();
        radio.setSelected(b.isSelected());
        int x = i.left - d.width + 8;
        int y = i.top + 8;
        SwingUtilities.paintComponent(
            g2, radio, b, x, y, d.width, d.height);
        g2.dispose();
      }
    }
  };
  return new JLayer<>(button, layer);
}