设计模式系列:迭代器模式

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概念

迭代器一般用于访问聚合对象内部元素。只暴露该暴露的，隐藏该隐藏的。比如隐藏掉容器内部的实现逻辑，只暴露
遍历的接口。

实现

类图

图片

代码

  • Iterator
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package com.littlehui.design.iterator;

/**
 * @Description TODO
 * @ClassName Iterator
 * @Author littlehui
 * @Date 2019/10/12 14:56
 * @Version 1.0
 **/
public interface Iterator {

    boolean hasNext();

    Object next();

    void remove();
}
  • IteratorCreator
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package com.littlehui.design.iterator;

/**
 * @Description TODO
 * @ClassName IteratorCreator
 * @Author littlehui
 * @Date 2019/10/12 14:57
 * @Version 1.0
 **/
public interface IteratorCreator {

    public Iterator createIterator();
}
  • MenuItem
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package com.littlehui.design.iterator;

/**
 * @Description TODO
 * @ClassName MenuItem
 * @Author littlehui
 * @Date 2019/10/12 14:57
 * @Version 1.0
 **/
public class MenuItem {

    private String code;

    private String menuName;

    public MenuItem(String code, String menuName) {
        this.code = code;
        this.menuName = menuName;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getMenuName() {
        return menuName;
    }

    public void setMenuName(String menuName) {
        this.menuName = menuName;
    }

    public void printMenu() {
        System.out.println("编码：" + code + "名称：" + menuName);
    }
}
  • MenuContainer
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package com.littlehui.design.iterator;


import java.util.ArrayList;
import java.util.List;

/**
 * @Description TODO
 * @ClassName MenuContainer
 * @Author littlehui
 * @Date 2019/10/12 14:57
 * @Version 1.0
 **/
public class MenuContainer implements IteratorCreator {

    private List<MenuItem> menuItems;

    public MenuContainer(List<MenuItem> menuItems) {
        this.menuItems = menuItems;
    }

    public MenuContainer() {

    }

    public void addMenuItem(MenuItem menuItem) {
        if (menuItems == null) {
            menuItems = new ArrayList<MenuItem>();
        }
        menuItems.add(menuItem);
    }

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

}
  • MenuContainerIterator
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package com.littlehui.design.iterator;

import java.util.ArrayList;
import java.util.List;

/**
 * @Description TODO
 * @ClassName MenuContainerIterator
 * @Author littlehui
 * @Date 2019/10/12 14:58
 * @Version 1.0
 **/
public class MenuContainerIterator implements Iterator {

    private List<MenuItem> menuItemList = null;

    private int currentIndex = -1;

    private int lastIndex = 0;

    public MenuContainerIterator(List<MenuItem> menuItemList) {
        this.menuItemList = menuItemList;
        lastIndex = menuItemList.size() - 1;
    }

    @Override
    public boolean hasNext() {
        if (currentIndex < lastIndex) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    public Object next() {
        MenuItem currentItem = menuItemList.get(++currentIndex);
        return currentItem;
    }

    @Override
    public void remove() {
        menuItemList.remove(currentIndex);
        --currentIndex;
        lastIndex = menuItemList.size() - 1;
    }
}
  • Client
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package com.littlehui.design.iterator;

import java.util.ArrayList;
import java.util.List;

/**
 * @Description TODO
 * @ClassName Client
 * @Author littlehui
 * @Date 2019/10/12 15:16
 * @Version 1.0
 **/
public class Client {

    public static void main(String[] args) {

        List<MenuItem> menuItemList = new ArrayList();
        menuItemList.add(new MenuItem("CODE_1", "第一个菜单"));
        menuItemList.add(new MenuItem("CODE_2", "第二个菜单"));
        menuItemList.add(new MenuItem("CODE_3", "第三个菜单"));

        MenuContainer menuContainer = new MenuContainer(menuItemList);
        Iterator iterator = menuContainer.createIterator();
        while (iterator.hasNext()) {
            MenuItem item = (MenuItem)iterator.next();
            if ("CODE_2".equals(item.getCode())) {
                iterator.remove();
            } else {
                item.printMenu();
            }
        }
    }
}
  • 执行
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Connected to the target VM, address: '127.0.0.1:51875', transport: 'socket'
编码：CODE_1名称：第一个菜单
编码：CODE_3名称：第三个菜单
Disconnected from the target VM, address: '127.0.0.1:51875', transport: 'socket'

Process finished with exit code 0

场景

如上简单描述了一个菜单面板利用迭代器模式的遍历过程。

总结