大话设计模式-迭代器模式

需求
设计一个公交车上售票员要求每个人买票的程序。
实现

abstract class Iterator
{  
    //第一个  
    public abstract Object first();    
    //下一个  
    public abstract Object next();  
    //时候到结尾  
    public abstract boolean isDone();  
    //当前对象  
    public abstract Object currentItem();  
} 

abstract class Aggregate
{  
    public abstract Iterator createIterator();  
} 

class ConcreteIterator extends Iterator 
{  
    private ConcreteAggregate aggregate;  
    private int current=0;    
    public ConcreteIterator(ConcreteAggregate aggregate) 
    {  
        this.aggregate=aggregate;  
    }  
    @Override  
    public Object first()
    {  
        return aggregate.get(0);  
    }  
    @Override  
    public Object next() 
    {  
        Object ret=null;  
        current++;  
        if(current<aggregate.count())
        {  
            ret=aggregate.get(current);  
        }  
        return ret;  
    }  
    @Override  
    public Object currentItem() 
    {  
        return aggregate.get(current);  
    }  
    @Override  
    public boolean isDone() 
    {  
        return current>=aggregate.count()?true:false;  
    }  
}  

import java.util.*;

class ConcreteAggregate extends Aggregate 
{  
    private List<Object> items=new ArrayList<Object>();    
    @Override  
    public Iterator createIterator() 
    {  
        return new ConcreteIterator(this);  
    }  
    public int count()
    {  
        return items.size();  
    }  
    public Object get(int index) 
    {  
        return items.get(index);  
    }  
    public void set(Object value) 
    {  
        items.add(value);  
    }  
}  

public class Main  
{  
    public static void main(String[] args)  
    {  
    	 ConcreteAggregate a=new ConcreteAggregate();  
         a.set("大鸟");  
         a.set("小菜");  
         a.set("行李");  
         a.set("老外");  
         a.set("公交内部员工");  
         a.set("小偷");  
         Iterator iterator=new ConcreteIterator(a);  
         while (!iterator.isDone())
         {  
             System.out.println(iterator.currentItem() + "\t请买车票.");  
             iterator.next();  
         }  
    }  
}

迭代器模式，又叫做游标模式，提供一种方法访问一个容器对象中各个元素，而又不需暴露该对象的内部细节。

在现代面向对象编程语言如C++，java等中已经实现了迭代器模式。

import java.util.*;

public class Main
{  
	public static void main(String[] args) 
	{  
		List<Integer> list=new ArrayList<Integer>();  
		Random random=new Random();  
        for(int i=0;i<10;i++)
        {  
            list.add(random.nextInt(20));  
        }  
        System.out.println("数组元素:"+list);  
        System.out.println("迭代结果:");  
        Iterator<Integer> iterator=list.iterator();  
        while(iterator.hasNext())
        {  
            System.out.print(iterator.next()+" ");  
        }  
    }  
}