迭代器模式

杨小杰

发布于 2019-07-04 16:30:17

5340

发布于 2019-07-04 16:30:17

文章被收录于专栏：JAVA知识总结与分享

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

情节

有两家餐厅，共有两个菜单，两家准备合并，每个餐厅都有一个销售系统，但是内部菜单的组成结构稍有不同，一个是用数组存储菜单对象，一个是用集合存储菜单对象

需求

将两个菜单合并显示

两个菜单代码

数组菜单

package com.iteratorPattern.arr;

import com.iteratorPattern.vo.MenuItem;

/**
 * @program: test
 * @description: 数组菜单
 * @author: Mr.Yang
 * @create: 2019-01-01 15:22
 **/
public class ArrMenu {
    static final int MAX_ITEMS=3;
    int items=0;
    MenuItem[] menuItems;
    public ArrMenu(){
        menuItems=new MenuItem[MAX_ITEMS];
        addItem("西红柿鸡蛋","有营养",10.00);
        addItem("酸辣白菜","好吃",11.00);
        addItem("酸辣土豆丝","特色菜",12.00);
    }

    private void addItem(String name,String description,Double price){
        MenuItem menuItem = new MenuItem(name, description, price);
        if(items>=MAX_ITEMS){
            System.err.println("menu is full,Can't add item to menu");
        }else{
            menuItems[items]=menuItem;
            items+=1;
        }
    }

    public MenuItem[] getItems(){
        return menuItems;
    }

}

list集合菜单

package com.iteratorPattern.list;

import com.iteratorPattern.vo.MenuItem;

import java.util.ArrayList;

/**
 * @program: test
 * @description: list集合菜单
 * @author: Mr.Yang
 * @create: 2019-01-01 15:32
 **/
public class ListMenu {
    ArrayList<MenuItem> menuItems;
    public ListMenu(){
        menuItems = new ArrayList<MenuItem>();
        addItem("紫菜鸡蛋汤","有营养的汤",6.00);
        addItem("豆腐脑","早餐必备",7.00);
        addItem("鱿鱼汤","补充大脑",8.00);
    }


    private void addItem(String name,String description,Double price){
        MenuItem menuItem = new MenuItem(name, description, price);
        menuItems.add(menuItem);
    }

    public ArrayList<MenuItem> getItems(){
        return menuItems;
    }
}

当前合并测试类

package com.iteratorPattern.test;

import com.iteratorPattern.arr.ArrMenu;
import com.iteratorPattern.list.ListMenu;
import com.iteratorPattern.vo.MenuItem;

import java.util.ArrayList;

/**
 * @program: test
 * @description: 测试1
 * @author: Mr.Yang
 * @create: 2019-01-01 15:38
 **/
public class TestOne {
    //打印菜单--菜类和汤类，需要遍历两次，如果再有一个会变成三次，四次…………
    public static void main(String[] args) {
        ArrMenu arrMenu = new ArrMenu();
        MenuItem[] items = arrMenu.getItems();
        for (int i = 0; i < items.length; i++) {
            MenuItem item = items[i];
            System.out.println("item name:"+item.getName());
            System.out.println("item description:"+item.getDescription());
            System.out.println("item price:"+item.getPrice());
        }
        ListMenu listMenu = new ListMenu();
        ArrayList listMenuItems = listMenu.getItems();
        for (int i = 0; i < listMenuItems.size(); i++) {
            MenuItem item = (MenuItem) listMenuItems.get(i);
            System.out.println("item name:"+item.getName());
            System.out.println("item description:"+item.getDescription());
            System.out.println("item price:"+item.getPrice());
        }
    }
}

整合后

创建迭代器

package com.iteratorPattern.Iterator;

/**
 * @program: test
 * @description: 迭代器接口
 * @author: Mr.Yang
 * @create: 2019-01-01 15:44
 **/
public interface Iterator {
    boolean hasNext();
    Object next();
}

添加数组遍历方式的迭代器

package com.iteratorPattern.arr;

import com.iteratorPattern.Iterator.Iterator;
import com.iteratorPattern.vo.MenuItem;

/**
 * @program: test
 * @description: 数组遍历方式迭代器
 * @author: Mr.Yang
 * @create: 2019-01-01 15:46
 **/
public class ArrMenuIterator implements Iterator {
    MenuItem[] items;
    int position=0;
    public ArrMenuIterator(MenuItem[] items){
        this.items=items;
    }

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

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

数组菜单添加创建迭代器的方法

package com.iteratorPattern.arr;

import com.iteratorPattern.Iterator.Iterator;
import com.iteratorPattern.vo.MenuItem;

/**
 * @program: test
 * @description: 数组菜单
 * @author: Mr.Yang
 * @create: 2019-01-01 15:22
 **/
public class ArrMenu {
    static final int MAX_ITEMS=3;
    int items=0;
    MenuItem[] menuItems;
    public ArrMenu(){
        menuItems=new MenuItem[MAX_ITEMS];
        addItem("西红柿鸡蛋","有营养",10.00);
        addItem("酸辣白菜","好吃",11.00);
        addItem("酸辣土豆丝","特色菜",12.00);
    }

    private void addItem(String name,String description,Double price){
        MenuItem menuItem = new MenuItem(name, description, price);
        if(items>=MAX_ITEMS){
            System.err.println("menu is full,Can't add item to menu");
        }else{
            menuItems[items]=menuItem;
            items+=1;
        }
    }

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

}

创建list迭代器

package com.iteratorPattern.list;

import com.iteratorPattern.Iterator.Iterator;
import com.iteratorPattern.vo.MenuItem;

import java.util.ArrayList;

/**
 * @program: test
 * @description: list迭代器
 * @author: Mr.Yang
 * @create: 2019-01-01 16:12
 **/
public class ListMenuIterator implements Iterator {
    ArrayList listMenus;
    int position=0;
    public ListMenuIterator(ArrayList listMenus){
        this.listMenus=listMenus;
    }

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

    public Object next() {
        MenuItem menuItem = (MenuItem) listMenus.get(position);
        position+=1;
        return menuItem;
    }
}

list集合菜单添加创建迭代器的方法

package com.iteratorPattern.list;

import com.iteratorPattern.Iterator.Iterator;
import com.iteratorPattern.vo.MenuItem;

import java.util.ArrayList;

/**
 * @program: test
 * @description: list集合菜单
 * @author: Mr.Yang
 * @create: 2019-01-01 15:32
 **/
public class ListMenu {
    ArrayList<MenuItem> menuItems;
    public ListMenu(){
        menuItems = new ArrayList<MenuItem>();
        addItem("紫菜鸡蛋汤","有营养的汤",6.00);
        addItem("豆腐脑","早餐必备",7.00);
        addItem("鱿鱼汤","补充大脑",8.00);
    }


    private void addItem(String name,String description,Double price){
        MenuItem menuItem = new MenuItem(name, description, price);
        menuItems.add(menuItem);
    }
    public Iterator createIterator(){
        return new ListMenuIterator(menuItems);
    }
}

测试

package com.iteratorPattern.test;

import com.iteratorPattern.Iterator.Iterator;
import com.iteratorPattern.arr.ArrMenu;
import com.iteratorPattern.list.ListMenu;
import com.iteratorPattern.vo.MenuItem;

/**
 * @program: test
 * @description: 测试2
 * @author: Mr.Yang
 * @create: 2019-01-01 16:17
 **/
public class TestTwo {
    public static void main(String[] args) {
        ArrMenu arrMenu = new ArrMenu();
        ListMenu listMenu = new ListMenu();
        System.out.println("---------------数组 菜类---------------");
        printMenu(arrMenu.createIterator());
        System.out.println("---------------集合 汤类---------------");
        printMenu(listMenu.createIterator());
    }
    private static void printMenu(Iterator iterator){
        while (iterator.hasNext()){
            MenuItem next = (MenuItem) iterator.next();
            System.out.println("menu name is :"+next.getName());
            System.out.println("menu description is :"+next.getDescription());
            System.out.println("menu price is :"+next.getPrice());
        }
    }
}

测试结果

---------------数组 菜类---------------
menu name is :西红柿鸡蛋
menu description is :有营养
menu price is :10.0
menu name is :酸辣白菜
menu description is :好吃
menu price is :11.0
menu name is :酸辣土豆丝
menu description is :特色菜
menu price is :12.0
---------------集合 汤类---------------
menu name is :紫菜鸡蛋汤
menu description is :有营养的汤
menu price is :6.0
menu name is :豆腐脑
menu description is :早餐必备
menu price is :7.0
menu name is :鱿鱼汤
menu description is :补充大脑
menu price is :8.0

说明

此处不用java.util下面的迭代器是为了更好的了解迭代器是如何工作的，java.util比我们所实现的迭代器多了一个remove方法，如果有其他需求，自定义的迭代器相比于java.util更易拓展。

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