public class Main extends JavaPlugin {

  @Override public void onEnable() {
    Menu menu = new MenuBuilder(27, "Example", this)
            .set(13, new ItemStack(Material.PLAYER_HEAD, 1), (player, itemStack) -> player.sendMessage(ChatColor.GREEN + itemStack.getType().name()))
            .fillEmpty(new ItemStack(Material.BLACK_STAINED_GLASS, 1))
            .close(event -> event.getPlayer().sendMessage(ChatColor.GREEN + "You have closed the menu!"))
            .create();

    menu.open(player);
  }
}