JAVA设计模式---迭代器模式

1、定义： 提供一种方法顺序访问一个聚合对象中的各个元素，而又不暴露其内部的表示。

2、实例：
1）需求：
菜单（煎饼屋菜单、餐厅菜单和咖啡菜单）采用不同的集合存取（ArrayList,String[],Hashtable）,使用迭代器模式使服务员（waitress）能够不依赖于具体菜单而实现打印菜单操作。

2）代码实现：

　　a）菜单接口及实体类：

public interface Menu {
    public Iterator createIterator();
}

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

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    public boolean isVegetarian() {
        return vegetarian;
    }

    public void setVegetarian(boolean vegetarian) {
        this.vegetarian = vegetarian;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

　　b) 菜单具体实现

public class PancakeHouseMenu implements Menu {
    ArrayList menuItems;

    public PancakeHouseMenu() {
        menuItems = new ArrayList();
        addItem("kobe‘s pancake breakfast","pancakes with eggs",false,2.99);
        addItem("lilei‘s pancake breakfast", "pancakes with toast", false, 3.59);
    }

    public void addItem(String s, String s1, boolean b, double v) {
        MenuItem menuItem = new MenuItem(s,s1,b,v);
        menuItems.add(menuItem);
    }

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

public class DinnerMenu implements Menu {
    private static final int MAX_SIZE = 6;
    int numOfItems = 0;
    MenuItem[] menuItems;

    public DinnerMenu() {
        menuItems = new MenuItem[MAX_SIZE];
        addItem("Vegetarian BLT","Bacon with tomato",true,2.99);
        addItem("Hot dog","With onions and cheese",false,3.05);
    }

    private void addItem(String s, String s1, boolean b, double v) {
        MenuItem menuItem = new MenuItem(s,s1,b,v);
        if(numOfItems >= MAX_SIZE){
            System.err.println("sorry,menu is full!");
        }else{
            menuItems[numOfItems]=menuItem;
            numOfItems = numOfItems + 1;
        }
    }

    @Override
    public Iterator createIterator() {
        return new DinerMenuIterator(menuItems);
    }
}

public class CoffeeMenu implements Menu {
    Hashtable menuItems = new Hashtable();

    public CoffeeMenu() {
        addItem("Mocha","Han Meimei order on couple of Mocha",false,3.01);
    }

    private void addItem(String s, String s1, boolean b, double v) {
        MenuItem menuItem = new MenuItem(s,s1,b,v);
        menuItems.put(menuItem.getName(),menuItem);
    }

    @Override
    public Iterator createIterator() {
        return menuItems.values().iterator();
    }
}

　　c) 数组没有.iterator()方法，需要具体实现

public class DinerMenuIterator implements Iterator {
    MenuItem[] list;
    int position = 0;

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

    @Override
    public boolean hasNext() {
        if(position>=list.length || list[position] == null){
            return false;
        }else{
            return true;
        }
    }

    @Override
    public Object next() {
        MenuItem menuItem = list[position];
        position = position + 1;
        return menuItem;
    }

    @Override
    public void remove() {
        if(position <=0){
            throw new IllegalStateException("now  you can not remove an item");
        }
        if(list[position] != null){
            for(int i=position-1;i<(list.length-1);i++){
                list[i] = list[i+1];
            }
            list[list.length-1]=null;
        }
    }
}

　　d) waitress实现

public class Waitress {
    Menu pancakeHouseMenu;
    Menu dinnerMenu;
    Menu coffeeMenu;

    public Waitress(Menu pancakeHouseMenu, Menu dinnerMenu, Menu coffeeMenu) {
        this.pancakeHouseMenu = pancakeHouseMenu;
        this.dinnerMenu = dinnerMenu;
        this.coffeeMenu = coffeeMenu;
    }

    public void printMenu(){
        Iterator pancakeHouseIterator = pancakeHouseMenu.createIterator();
        Iterator dinnerIterator = dinnerMenu.createIterator();
        Iterator coffeeIterator = coffeeMenu.createIterator();
        System.out.println("Menu\n=====Breakfast==start======");
        printMenu(pancakeHouseIterator);
        System.out.println("Menu\n=====Breakfast===end=====");
        System.out.println("Menu\n=====Lunch==start======");
        printMenu(dinnerIterator);
        System.out.println("Menu\n=====Lunch===end=====");
        System.out.println("Menu\n=====Coffee==start======");
        printMenu(coffeeIterator);
        System.out.println("Menu\n=====Coffee===end=====");
    }

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

　　e) 测试类

public class MenuTest {
    public static void main(String[] args) {
        PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
        DinnerMenu dinnerMenu = new DinnerMenu();
        CoffeeMenu coffeeMenu = new CoffeeMenu();

        Waitress waitress = new Waitress(pancakeHouseMenu,dinnerMenu,coffeeMenu);
        waitress.printMenu();
    }
}

　　测试结果：

Menu
=====Breakfast==start======
kobe‘s pancake breakfast,
2.99,
pancakes with eggs
lilei‘s pancake breakfast,
3.59,
pancakes with toast
Menu
=====Breakfast===end=====
Menu
=====Lunch==start======
Vegetarian BLT,
2.99,
Bacon with tomato
Hot dog,
3.05,
With onions and cheese
Menu
=====Lunch===end=====
Menu
=====Coffee==start======
Mocha,
3.01,
Han Meimei order on couple of Mocha
Menu
=====Coffee===end=====