public interface IMenuRepository { void AddMenu(Menu menu); } public class MenuRepository : IMenuRepository { private ListIn this example, we have defined an interface called IMenuRepository with a method called AddMenu, which takes a Menu object as a parameter. The MenuRepository class implements this interface and has a private List of Menu objects. The AddMenu method adds the passed-in menu item to the list. In this case, it appears that we are not using any external library.