【设计模式】迭代器模式

定义：迭代器模式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。

package cn.sp.test1;


/**
 * 菜单类
 * Created by 2YSP on 2017/7/14.
 */
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 void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    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;
    }

    @Override
    public String toString() {
        return "MenuItem{" +
                "name='" + name + '\'' +
                ", description='" + description + '\'' +
                ", vegetarian=" + vegetarian +
                ", price=" + price +
                '}';
    }
}

package cn.sp.test1;

import java.util.Iterator;

/**
 * Created by 2YSP on 2017/7/14.
 */
public class DinnerMenu {
    static final  int MAX_ITEMS = 6;
    int numberOfItems = 0;
    MenuItem[] menuItems;

    public DinnerMenu(){
        menuItems = new MenuItem[MAX_ITEMS];
        addItem("Vegetarian BLT","bacon ",true,2.99);
        addItem("BLT","Bacon with lettuce & tomato on whole wheat",false,2.99);
        addItem("Soup of the day","with a side of potato salad",false,3.29);
    }

    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 MenuItem[] getMenuItems(){不再需要
//        return menuItems;
//    }

    public Iterator createIterator(){
        return  new DinnerMenuIterator(menuItems);
    }
}

package cn.sp.test1;

import java.util.Iterator;

/**
 * Created by 2YSP on 2017/7/14.
 */
public class DinnerMenuIterator implements Iterator {
    MenuItem[] menuItems;
    int position = 0;//记录当前位置

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

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

    public boolean hasNext(){
        if(position > menuItems.length || menuItems[position] == null){//不但要检查是否超过数组长度，还要检查下一项是否为Null
            return  false;
        }else {
            return  true;
        }
    }

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

        if (menuItems[position-1] != null ){
            for(int i = position-1;i < (menuItems.length -1);i++){
                menuItems[i] = menuItems[i+1];
            }
            menuItems[menuItems.length-1] = null;
        }
    }
}

package cn.sp.test1;

import java.util.ArrayList;
import java.util.Iterator;

/**
 * Created by 2YSP on 2017/7/14.
 */
public class PancakeHouseMenu {
    ArrayList menuItems;

    public PancakeHouseMenu(){
        menuItems = new ArrayList();
        addItem("ddf","Pancakes with scrambled eggs,and toast",true,2.99);
        addItem("Regular ","Pancakes with fried eggs,sausage",false,2.99);
        addItem("Blueberry","Pancakes made with fresh blueberries",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);
    }

//    public ArrayList getMenuItems(){
//        return menuItems;
//    }

    public Iterator createIterator(){
//        return  new PancakeHouseMenuIterator(menuItems);
        return  menuItems.iterator();//ArrayList有迭代器
    }
}

package cn.sp.test1;

import java.util.ArrayList;
import java.util.Iterator;

/**
 * Created by 2YSP on 2017/7/14.
 */
public class PancakeHouseMenuIterator implements Iterator {
    ArrayList menuItems;
    int position = 0;

    public  PancakeHouseMenuIterator(ArrayList items){
        menuItems = items;
    }

    public Object next(){
        Object obj = menuItems.get(position);
        position = position + 1;
        return obj;
    }

    public boolean hasNext(){
        if(position >= menuItems.size() || menuItems.get(position) == null){
            return  false;
        }else{
            return  true;
        }
    }
}

package cn.sp.test1;

import java.util.Iterator;

/**
 * Created by 2YSP on 2017/7/14.
 */
public class Test {
    public static void main(String[] args) {
        PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
        DinnerMenu dinnerMenu = new DinnerMenu();
        Iterator it1 = pancakeHouseMenu.createIterator();
        while (it1.hasNext()){
            System.out.println(((MenuItem)it1.next()).toString());
        }
        System.out.println("===================");
        Iterator it2 = dinnerMenu.createIterator();
        while (it2.hasNext()){
            System.out.println(((MenuItem)it2.next()).toString());
        }
    }
}

运行结果：

MenuItem{name='ddf', description='Pancakes with scrambled eggs,and toast', vegetarian=true, price=2.99}
MenuItem{name='Regular ', description='Pancakes with fried eggs,sausage', vegetarian=false, price=2.99}
MenuItem{name='Blueberry', description='Pancakes made with fresh blueberries', vegetarian=true, price=3.49}
===================
MenuItem{name='Vegetarian BLT', description='bacon ', vegetarian=true, price=2.99}
MenuItem{name='BLT', description='Bacon with lettuce & tomato on whole wheat', vegetarian=false, price=2.99}
MenuItem{name='Soup of the day', description='with a side of potato salad', vegetarian=false, price=3.29}