java 中迭代器的使用方法详解

public interface Menu<T> {
  Iterator<T> createIterator();
}

public class MenuItem {
  private String name;
  private String description;
  private boolean vegetarian;
  private double price;

  public MenuItem(String name, String description, boolean vegetarian, double price) {
    this.name = name;
    this.description = description;
    this.vegetarian = vegetarian;
    this.price = price;
  }

  public String getName() {
    return name;
  }

  public String getDescription() {
    return description;
  }

  public boolean isVegetarian() {
    return vegetarian;
  }

  public double getPrice() {
    return price;
  }
}

public class DinerMenu implements Menu<MenuItem> {
  private static final int MAX_ITEMS = 6;
  private int numberOfItems = 0;
  private MenuItem[] menuItems;

  public DinerMenu() {
    menuItems = new MenuItem[MAX_ITEMS];
    addItem("Vegetarian BLT", "(Fakin') Bacon with lettuce & tomato on whole wheat", true, 2.99);
    addItem("BLT", "Bacon with lettuce & tomato on whole wheat", false, 2.99);
    addItem("Soup of the day", "Soup of the day, with a side of potato salad", false, 3.29);
    addItem("Hotdog", "A hot dog, with saurkraut, relish, onions, topped with cheese", false, 3.05);
  }

  public void addItem(String name, String description, boolean vegetarian, double price) {
    MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
    if (numberOfItems >= MAX_ITEMS) {
      System.out.println("Sorry, menu is full, Can't add item to menu");
    } else {
      menuItems[numberOfItems] = menuItem;
      numberOfItems++;
    }
  }

  @Deprecated
  public MenuItem[] getMenuItems() {
    return menuItems;
  }

  public Iterator<MenuItem> createIterator() {
    return new DinerMenuIterator(menuItems);
  }
}
public class PancakeHouseMenu implements Menu<MenuItem> {
  private ArrayList<MenuItem> menuItems;

  public PancakeHouseMenu() {
    menuItems = new ArrayList<>();
    addItem("K&B's Pancake Breakfast", "Pancakes with scrambled eggs, and toast", true, 2.99);
    addItem("Regular Pancake Breakfast", "Pancakes with fried eggs, sausage", false, 2.99);
    addItem("Blueberry Pancakes", "Pancakes made with fresh blueberries", true, 3.49);
    addItem("Waffles", "Waffles, with your choice of blueberries or strawberries", true, 3.49);
  }

  public void addItem(String name, String description, boolean vegetarian, double price) {
    MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
    menuItems.add(menuItem);
  }

  @Deprecated
  public ArrayList<MenuItem> getMenuItems() {
    return menuItems;
  }

  public Iterator<MenuItem> createIterator() {
    return menuItems.iterator();
  }
}

public interface Iterator<T> {
  boolean hasNext();
  T next();
}

public class DinerMenuIterator implements Iterator<MenuItem> {
  private MenuItem[] items;
  private int position = 0;

  public DinerMenuIterator(MenuItem[] items) {
    this.items = items;
  }

  @Override
  public boolean hasNext() {
    return position < items.length && items[position] != null;
  }

  @Override
  public MenuItem next() {
    return items[position++];
  }

  @Override
  public void remove() {
    if (position <= 0) {
      throw new IllegalStateException("You can't remove an item until you've done at least one next()");
    }

    if (items[position - 1] != null) {
      for (int i = position - 1; i < items.length - 1; i++) {
        items[i] = items[i + 1];
      }
      items[items.length - 1] = null;
    }
  }
}
public class PancakeHouseIterator implements Iterator<MenuItem> {
  private ArrayList<MenuItem> items;
  private int position = 0;

  public PancakeHouseIterator(ArrayList<MenuItem> items) {
    this.items = items;
  }

  @Override
  public boolean hasNext() {
    return position < items.size();
  }

  @Override
  public MenuItem next() {
    return items.get(position++);
  }
}

public class Waitress {
  private Menu<MenuItem> pancakeHouseMenu;
  private Menu<MenuItem> dinerMenu;

  public Waitress(Menu<MenuItem> pancakeHouseMenu, Menu<MenuItem> dinerMenu) {
    this.pancakeHouseMenu = pancakeHouseMenu;
    this.dinerMenu = dinerMenu;
  }

  public void printMenu() {
    Iterator<MenuItem> pancakeIterator = pancakeHouseMenu.createIterator();
    Iterator<MenuItem> dinerIterator = dinerMenu.createIterator();
    System.out.println("MENU\n----\nBREAKFAST");
    printMenu(pancakeIterator);
    System.out.println("\nLUNCH");
    printMenu(dinerIterator);

  }

  private void printMenu(Iterator<MenuItem> iterator) {
    while (iterator.hasNext()) {
      MenuItem menuItem = iterator.next();
      System.out.print(menuItem.getName() + ", ");
      System.out.print(menuItem.getPrice() + " -- ");
      System.out.println(menuItem.getDescription());
    }
  }
}