JFrameのデフォルトWindow装飾タイトルバー上にJButtonを配置する

class ExtraBarPositionHandler extends WindowAdapter implements ComponentListener {
  private final JWindow extraBar;

  protected ExtraBarPositionHandler(JWindow extraBar) {
    this.extraBar = extraBar;
  }

  @Override public void windowActivated(WindowEvent e) {
    extraBar.setBackground(UIManager.getColor("activeCaption"));
  }

  @Override public void windowDeactivated(WindowEvent e) {
    extraBar.setBackground(UIManager.getColor("inactiveCaption"));
  }

  @Override public void windowOpened(WindowEvent e) {
    setLocationRelativeTo(e.getWindow());
    extraBar.setVisible(true);
  }

  @Override public void windowClosed(WindowEvent e) {
    extraBar.setVisible(false);
  }

  @Override public void windowIconified(WindowEvent e) {
    extraBar.setVisible(false);
  }

  @Override public void windowDeiconified(WindowEvent e) {
    setLocationRelativeTo(e.getWindow());
    extraBar.setVisible(true);
  }

  @Override public void componentResized(ComponentEvent e) {
    // System.out.println("componentResized");
    // ???: setLocationRelativeTo(e.getComponent());
    EventQueue.invokeLater(() -> setLocationRelativeTo(e.getComponent()));
  }

  @Override public void componentMoved(ComponentEvent e) {
    setLocationRelativeTo(e.getComponent());
  }

  @Override public void componentShown(ComponentEvent e) {
    setLocationRelativeTo(e.getComponent());
    extraBar.setVisible(true);
  }

  @Override public void componentHidden(ComponentEvent e) {
    extraBar.setVisible(false);
  }

  private void setLocationRelativeTo(Component p) {
    EventQueue.invokeLater(() -> updateExtraBarLocation(p));
  }

  private void updateExtraBarLocation(Component p) {
    JRootPane root = SwingUtilities.getRootPane(p);
    Icon iconifyIcon = UIManager.getIcon("InternalFrame.iconifyIcon");
    Insets zeroIns = new Insets(0, 0, 0, 0);
    Border bdr = root.getBorder();
    Insets ins = bdr == null ? zeroIns : bdr.getBorderInsets(root);
    if (p instanceof Frame &&
        ((Frame) p).getExtendedState() == Frame.MAXIMIZED_BOTH) {
      ins = zeroIns;
    }
    JButton iconifyIconButton = SwingUtils
        .descendants(root)
        .filter(JButton.class::isInstance)
        .map(JButton.class::cast)
        .filter(b -> Objects.equals(b.getIcon(), iconifyIcon))
        .findFirst()
        .orElse(null);
    Point pt = iconifyIconButton == null
        ? new Point()
        : iconifyIconButton.getLocation();
    SwingUtilities.convertPointToScreen(pt, root);
    int x = pt.x - extraBar.getWidth();
    int y = p.getY() + ins.top + 1;
    extraBar.setLocation(x, y);
  }
}