JToolBar内にJMenuBarを配置して分離・移動可能に設定する

JMenuBar menuBar = new JMenuBar();
menuBar.add(makeMenu("JMenu 1"));

JMenu menu2 = makeMenu("JMenu 2");
menu2.addMenuListener(new MenuListener() {
  private boolean isFloating(Component c) {
    Container p = SwingUtilities.getAncestorOfClass(JToolBar.class, c);
    return p instanceof JToolBar &&
        ((BasicToolBarUI) ((JToolBar) p).getUI()).isFloating();
  }

  @Override public void menuSelected(MenuEvent e) {
    JMenu menu = (JMenu) e.getSource();
    if (menu.isTopLevelMenu() && !isFloating(menu)) {
      Dimension d = menu.getPreferredSize();
      Component cp = menu.getRootPane().getContentPane();
      Point pt = SwingUtilities.convertPoint(
          menu.getParent(), menu.getLocation(), cp);
      pt.y += d.height * 2;
      if (!cp.getBounds().contains(pt)) {
        EventQueue.invokeLater(() -> {
          JPopupMenu popup = menu.getPopupMenu();
          Rectangle bounds = popup.getBounds();
          Point loc = menu.getLocationOnScreen();
          loc.y -= bounds.height + UIManager.getInt("Menu.menuPopupOffsetY");
          popup.setLocation(loc);
        });
      }
    }
  }

  @Override public void menuDeselected(MenuEvent e) {
    // Do nothing
  }

  @Override public void menuCanceled(MenuEvent e) {
    // Do nothing
  }
});
menuBar.add(menu2);

JToolBar toolBar = new JToolBar() {
  @Override public void updateUI() {
    super.updateUI();
    setLayout(new BorderLayout());
  }
};
toolBar.add(menuBar);

add(toolBar, BorderLayout.NORTH);