Menu.createIterator is one-shot iterator only

[JerryYangSH]

The Menu.createIterator is one-shot iterator, not support re-iterating. This looks a bug to me. Could you have a chance to fix this?

public class Menu extends MenuComponent {
    private Iterator iterator; // Seriously!
    private List<MenuComponent> menuComponents;
...
    public Iterator<MenuComponent> createIterator() {
		if (iterator == null) {
			iterator = new CompositeIterator(menuComponents.iterator());
		}
		return iterator; // the `iterator' never resets to null once it's set.
	}
...
}

...
headfirst.designpatterns.composite.menuiterator
public class MenuTestDrive {
	public static void main(String args[]) {
...
		Waitress waitress = new Waitress(allMenus);
   
		waitress.printVegetarianMenu();
		waitress.printVegetarianMenu(); // calling printVegetarianMenu again will print nothing
	}

Output is : 

VEGETARIAN MENU
----
  K&B's Pancake Breakfast(v), 2.99
     -- Pancakes with scrambled eggs, and toast
  Blueberry Pancakes(v), 3.49
     -- Pancakes made with fresh blueberries, and blueberry syrup
  Waffles(v), 3.59
     -- Waffles, with your choice of blueberries or strawberries
  Vegetarian BLT(v), 2.99
     -- (Fakin') Bacon with lettuce & tomato on whole wheat
  Steamed Veggies and Brown Rice(v), 3.99
     -- A medly of steamed vegetables over brown rice
  Pasta(v), 3.89
     -- Spaghetti with Marinara Sauce, and a slice of sourdough bread
  Apple Pie(v), 1.59
     -- Apple pie with a flakey crust, topped with vanilla icecream
  Cheesecake(v), 1.99
     -- Creamy New York cheesecake, with a chocolate graham crust
  Sorbet(v), 1.89
     -- A scoop of raspberry and a scoop of lime
  Veggie Burger and Air Fries(v), 3.99
     -- Veggie burger on a whole wheat bun, lettuce, tomato, and fries
  Burrito(v), 4.29
     -- A large burrito, with whole pinto beans, salsa, guacamole

VEGETARIAN MENU
----
Process finished with exit code 0