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。