深入浅出设计模式-010：迭代器模式（Iterator Pattern）

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本文通过餐厅菜单的例子，详细介绍了迭代器模式的概念及其实现方式。该模式允许客户端以一致的方式遍历不同的集合类型，而无需了解这些类型的内部结构。

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深入浅出设计模式-010：迭代器模式（Iterator Pattern）

一：餐厅举例
    //菜单项
    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{
            get { return name; }
        }
        public String getDescription{
            get { return description; }
        }
        public Boolean getVegetatian{
            get { return vegetarian; }
        }
        public Double getPrice{
            get { return price; }
        }
    }
    //用ArrayList
    class PancakeHouseMenu{
        private ArrayList menuItems;
        public PancakeHouseMenu(){
            menuItems = new ArrayList();
            addItem("11", "11", true, 2);
        }
        public void addItem(String name, String description, Boolean vegetarian, Double price){
            menuItems.Add(new MenuItem(name, description, vegetarian, price));
        }
        public ArrayList getMenuItems{
            get { return menuItems; }
        }
    }
    //用数组
    class DinerMenu{
        public const int MAX_ITEMS = 6;
        int numberOfItems = 0;
        MenuItem[] menuItems;
        public DinerMenu(){
            menuItems = new MenuItem[MAX_ITEMS];
            addItem("21", "21", false, 2);
        }
        public void addItem(String name, String description, Boolean vegetarian, Double price){
            if (numberOfItems < MAX_ITEMS - 1){
                menuItems[numberOfItems++] = new MenuItem(name, description, vegetarian, price);
            }
        }
        public MenuItem[] getMenuItems{
            get { return menuItems; }
        }
    }
    //遍历时
    static void Main(string[] args)
    {
        PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
        ArrayList breakfastItems = pancakeHouseMenu.getMenuItems;

DinerMenu dinerMenu = new DinerMenu();
MenuItem[] lunchItems = dinerMenu.getMenuItems;

        for (int index = 0; index < breakfastItems.Count; index++)
        {
            MenuItem menuItem = (MenuItem)breakfastItems[index];
        }
        for (int index = 0; index < lunchItems.Length; index++)
        {
            MenuItem menuItem = lunchItems[index];
        }
    }

二：我们希望的结果是：利用迭代器操作，屏蔽内部细节
    static void Main(string[] args)
    {
        PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();

        DinerMenu dinerMenu = new DinerMenu();

        Iterator iterator1 = pancakeHouseMenu.createIterator();
        while (iterator1.hasNext())
        {
            MenuItem menuItem = (MenuItem)iterator1.next();
        }
        Iterator iterator2 = dinerMenu.createIterator();
        while (iterator2.hasNext())
        {
            MenuItem menuItem = (MenuItem)iterator2.next();
        }
    }

    public interface Iterator{
        Boolean hasNext();
        Object next();
    }
    class DinerMenuIterator : Iterator{
        MenuItem[] items;
        int position = 0;
        public DinerMenuIterator(MenuItem[] items){
            this.items = items;
        }
        public Boolean hasNext(){
            if (position >= items.Length || items[position] == null){
                return false;
            }
            return true;
        }
        public Object next(){
            return items[position++];
        }
    }
    class PancakeHouseMenuIterator : Iterator{
        private ArrayList items;
        int position = 0;
        public PancakeHouseMenuIterator(ArrayList items){
            this.items = items;
        }
        public Boolean hasNext(){
            if (position >= items.Count || items[position] == null){
                return false;
            }
            return true;
        }
        public Object next(){
            return items[position++];
        }
    }
    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{
            get { return name; }
        }
        public String getDescription{
            get { return description; }
        }
        public Boolean getVegetatian{
            get { return vegetarian; }
        }
        public Double getPrice{
            get { return price; }
        }
    }

    class PancakeHouseMenu{
        private ArrayList menuItems;
        public PancakeHouseMenu(){
            menuItems = new ArrayList();
            addItem("11", "11", true, 2);
        }
        public void addItem(String name, String description, Boolean vegetarian, Double price){
            menuItems.Add(new MenuItem(name, description, vegetarian, price));
        }
        //关键部分
        public Iterator createIterator(){
            return new PancakeHouseMenuIterator(menuItems);
        }
    }
    class DinerMenu{
        public const int MAX_ITEMS = 6;
        int numberOfItems = 0;
        MenuItem[] menuItems;
        public DinerMenu(){
            menuItems = new MenuItem[MAX_ITEMS];
            addItem("21", "21", false, 2);
        }
        public void addItem(String name, String description, Boolean vegetarian, Double price){
            if (numberOfItems < MAX_ITEMS - 1){
                menuItems[numberOfItems++] = new MenuItem(name, description, vegetarian, price);
            }
        }
        //关键部分
        public Iterator createIterator(){
            return new DinerMenuIterator(menuItems);
        }
    }