Head First设计形式-迭代器模式

Head First设计模式-迭代器模式

一、整体代码

       Iterator.java

public interface Iterator {
	boolean hasNext();
	Object next();
}

      DinerMenuIterator.java

public class DinerMenuIterator implements Iterator {
	MenuItem[] items;
	int position = 0;
 
	public DinerMenuIterator(MenuItem[] items) {
		this.items = items;
	}
 
	public Object next() {
		MenuItem menuItem = items[position];
		position = position + 1;
		return menuItem;
	}
 
	public boolean hasNext() {
		if (position >= items.length || items[position] == null) {
			return false;
		} else {
			return true;
		}
	}
}

       PancakeHouseMenuIterator.java

import java.util.ArrayList;

public class PancakeHouseMenuIterator implements Iterator {
	private ArrayList items;
	private int position = 0;
 
	public PancakeHouseMenuIterator(ArrayList items) {
		this.items = items;
	}
 
	public Object next() {
		Object object = items.get(position);
		position = position + 1;
		return object;
	}
 
	public boolean hasNext() {
		if (position >= items.size()) {
			return false;
		} else {
			return true;
		}
	}
}

      DinerMenu.java

public class DinerMenu  {
	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);
		addItem("Steamed Veggies and Brown Rice",
			"Steamed vegetables over brown rice", true, 3.99);
		addItem("Pasta",
			"Spaghetti with Marinara Sauce, and a slice of sourdough bread",
			true, 3.89);
	}
  
	public void addItem(String name, String description, 
	                     boolean vegetarian, double price) 
	{
		MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
		if (numberOfItems >= MAX_ITEMS) {
			System.err.println("Sorry, menu is full!  Can't add item to menu");
		} else {
			menuItems[numberOfItems] = menuItem;
			numberOfItems = numberOfItems + 1;
		}
	}
 
  
	public Iterator createIterator() {
		return new DinerMenuIterator(menuItems);
	}
 
	// other menu methods here
}

      PancakeHouseMenu.java

import java.util.ArrayList;

public class PancakeHouseMenu {
	private ArrayList 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,
			3.59);
	}

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

	// other menu methods here
}

       MenuItem.java

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 double getPrice() {
		return price;
	}
  
	public boolean isVegetarian() {
		return vegetarian;
	}
	public String toString() {
		return (name + ", $" + price + "\n   " + description);
	}
}

     Waitress.java

import java.util.*;
public class Waitress {
	private PancakeHouseMenu pancakeHouseMenu;
	private DinerMenu dinerMenu;
 
	public Waitress(PancakeHouseMenu pancakeHouseMenu, DinerMenu dinerMenu) {
		this.pancakeHouseMenu = pancakeHouseMenu;
		this.dinerMenu = dinerMenu;

	}
 
	public void printMenu() {
		System.out.println("MENU\n----\nBREAKFAST");
		printMenu(pancakeHouseMenu.createIterator());
		System.out.println("\nLUNCH");
		printMenu(dinerMenu.createIterator());
	}
 
	private void printMenu(Iterator iterator) {
		while (iterator.hasNext()) {
			MenuItem menuItem = (MenuItem)iterator.next();
			System.out.print(menuItem.getName() + ", ");
			System.out.print(menuItem.getPrice() + " -- ");
			System.out.println(menuItem.getDescription());
		}
	}

}

     MenuTestDrive.java

import java.util.*;

public class MenuTestDrive {
	public static void main(String args[]) {
		PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
		DinerMenu dinerMenu = new DinerMenu();
		Waitress waitress = new Waitress(pancakeHouseMenu, dinerMenu);
		waitress.printMenu();
	}
}

二、结果

三、解释

       迭代器模式：提供一种方法一个聚合对象中的各个元素，而不是暴露其内部的显示。

       OO原则：类只有一个改变的理由。