迭代器模式

ref: http://blog.csdn.net/fengzhe0411/article/details/7187905

迭代器模式我们在jdbc，和容器中经常用到。每个容器要想遍历的时候，我们会调用

xxx.iterator();返回迭代器。

首先我们先看看迭代器接口

Method Summary
 boolean    hasNext() 
          Returns true if the iteration has more elements.
 E    next() 
          Returns the next element in the iteration.
 void    remove() 
          Removes from the underlying collection the last element returned by the iterator (optio

3个方法，hashnext 还有下一个元素吗？  next:获得下一个元素的对象
迭代器屏蔽了各种实现细节，对于hashmap,LinkedList都可以用迭代器访问，而不用了解内部实现的细节。

下面使用Iterator接口，和Collection接口实现一个LinkedList集合。

import java.util.Collection;
import java.util.Iterator;

//链表迭代器的实现
class Node
{
    Object n;
    Node next;
    public Node(Object n)
    {
        this.n=n;
        
    }
    
}
public class LinkList  implements Collection{
    Node head=null;
    Node tail=null;
    int size=0;
   
    
    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        LinkList l=new LinkList();
        l.add(new Node("zhang"));
        l.add(new Node("xiao"));
        l.add(new Node("er"));
        l.add(new Node("shi"));
        Iterator iter=l.iterator();
        while(iter.hasNext())
        {
            System.out.println(iter.next());
            
        }

    }

    @Override
    public int size() {
        // TODO Auto-generated method stub
        return size;
    }

    @Override
    public boolean isEmpty() {
        if(head==null) return true;
        return false;
    }

    @Override
    public boolean contains(Object o) {
        // TODO Auto-generated method stub
        Node p=head;
        while(p!=null)
        {
            if(p.n==o) return true;
            p=p.next;
        }
        return false;
    }

    @Override
    public Iterator iterator() {
        // TODO Auto-generated method stub
        return new LinkListIterator();
    }

    @Override
    public Object[] toArray() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Object[] toArray(Object[] a) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public boolean add(Object e) {
        // TODO Auto-generated method stub
        if(head==null)
        {
            head=(Node) e;
            tail=head;
        }
        else
        {
            tail.next=(Node) e;
            tail=tail.next;
            
        }
        return true;
    }

    @Override
    public boolean remove(Object o) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean containsAll(Collection c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean addAll(Collection c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean removeAll(Collection c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public boolean retainAll(Collection c) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public void clear() {
        // TODO Auto-generated method stub
        
    }
    private  class LinkListIterator implements Iterator
    {
        private Node current=head;

        @Override
        public boolean hasNext() {
            // TODO Auto-generated method stub
            if(current==null) return false;
            return true;
        }

        @Override
        public Object next() {
            Object o=current.n;
              current=current.next;
            return o;
        }

        @Override
        public void remove() {
            // TODO Auto-generated method stub
            
        }
        
        
    }

}