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

1 Method Summary
2  boolean    hasNext() 
3           Returns true if the iteration has more elements.
4  E    next() 
5           Returns the next element in the iteration.
6  void    remove() 
7           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。

  1 import java.util.Collection;
  2 import java.util.Iterator;
  3 
  4 //链表迭代器的实现
  5 class Node
  6 {
  7     Object n;
  8     Node next;
  9     public Node(Object n)
 10     {
 11         this.n=n;
 12         
 13     }
 14     
 15 }
 16 public class LinkList  implements Collection{
 17     Node head=null;
 18     Node tail=null;
 19     int size=0;
 20    
 21     
 22     /**
 23      * @param args
 24      */
 25     public static void main(String[] args) {
 26         // TODO Auto-generated method stub
 27         LinkList l=new LinkList();
 28         l.add(new Node("zhang"));
 29         l.add(new Node("xiao"));
 30         l.add(new Node("er"));
 31         l.add(new Node("shi"));
 32         Iterator iter=l.iterator();
 33         while(iter.hasNext())
 34         {
 35             System.out.println(iter.next());
 36             
 37         }
 38 
 39     }
 40 
 41     @Override
 42     public int size() {
 43         // TODO Auto-generated method stub
 44         return size;
 45     }
 46 
 47     @Override
 48     public boolean isEmpty() {
 49         if(head==null) return true;
 50         return false;
 51     }
 52 
 53     @Override
 54     public boolean contains(Object o) {
 55         // TODO Auto-generated method stub
 56         Node p=head;
 57         while(p!=null)
 58         {
 59             if(p.n==o) return true;
 60             p=p.next;
 61         }
 62         return false;
 63     }
 64 
 65     @Override
 66     public Iterator iterator() {
 67         // TODO Auto-generated method stub
 68         return new LinkListIterator();
 69     }
 70 
 71     @Override
 72     public Object[] toArray() {
 73         // TODO Auto-generated method stub
 74         return null;
 75     }
 76 
 77     @Override
 78     public Object[] toArray(Object[] a) {
 79         // TODO Auto-generated method stub
 80         return null;
 81     }
 82 
 83     @Override
 84     public boolean add(Object e) {
 85         // TODO Auto-generated method stub
 86         if(head==null)
 87         {
 88             head=(Node) e;
 89             tail=head;
 90         }
 91         else
 92         {
 93             tail.next=(Node) e;
 94             tail=tail.next;
 95             
 96         }
 97         return true;
 98     }
 99 
100     @Override
101     public boolean remove(Object o) {
102         // TODO Auto-generated method stub
103         return false;
104     }
105 
106     @Override
107     public boolean containsAll(Collection c) {
108         // TODO Auto-generated method stub
109         return false;
110     }
111 
112     @Override
113     public boolean addAll(Collection c) {
114         // TODO Auto-generated method stub
115         return false;
116     }
117 
118     @Override
119     public boolean removeAll(Collection c) {
120         // TODO Auto-generated method stub
121         return false;
122     }
123 
124     @Override
125     public boolean retainAll(Collection c) {
126         // TODO Auto-generated method stub
127         return false;
128     }
129 
130     @Override
131     public void clear() {
132         // TODO Auto-generated method stub
133         
134     }
135     private  class LinkListIterator implements Iterator
136     {
137         private Node current=head;
138 
139         @Override
140         public boolean hasNext() {
141             // TODO Auto-generated method stub
142             if(current==null) return false;
143             return true;
144         }
145 
146         @Override
147         public Object next() {
148             Object o=current.n;
149               current=current.next;
150             return o;
151         }
152 
153         @Override
154         public void remove() {
155             // TODO Auto-generated method stub
156             
157         }
158         
159         
160     }
161 
162 }