code: public List<MenuItem> getMenuItems(MenuItem item) {
          synchronized (subMenuItems) {
              ArrayList<MenuItem> menuItems = subMenuItems.get(item);
              return menuItems == null ? null : Collections.unmodifiableList(menuItems);
          }
      }
docs: Get a list of all menu items for a given submenu
  @param item the submenu to use
  @return a list of submenu items that's immutable