设计模式之Iterator

 迭代器模式：目前该模式已被整入到Java的Collection。

适用于：

• 访问一个聚合对象的内容而不暴露它的内部表示
• 支持聚合对象的多种遍历
• 为遍历不同的聚合结构提供统一的接口

下边用代码模拟Java的Iterator:

1. 定义Iterator接口，定义迭代接口方法

   /*
    * imitate the JDK Iterator
    */
   public interface Iterator<E> {
   	public E next();
   	public boolean hasNext();
   }

2. 定义Collection接口，及集合的通用方法如 添加，获取遍历，获得总实体数

   /**
    * @author lisa
    * imitate the Collection of JDK
    */
   public interface Collection<E> {
   	public void add(E e);
   	public int size();
   	public Iterator iterator();
   }

3. 分别定义集合类 ArrayList和LinkedList类，实现Collection接口，实现具体的方法

   /**
    * @author lisa
    * imitate the Collection of JDK
    */
   public interface Collection<E> {
   	public void add(E e);
   	public int size();
   	public Iterator iterator();
   }
   

    

   public class LinkedList<E> implements Collection<E> {
   	private Node head = null;
   	private Node tail = null;
   	private int size;
   	
   	@Override
   	public void add(E e) {
   		Node n = new Node(e,null);
   		if(head == null){
   			head = n;
   			tail = n;
   		}else{
   			tail.setNext(n);
   			tail = n;	
   		}
   			
   		size++;
   	}
   
   	@Override
   	public int size() {
   		// TODO Auto-generated method stub
   		return size;
   	}
   
   	@Override
   	public Iterator iterator() {
   		return new LinkedListIterator();
   	}
   	
   	private class LinkedListIterator implements Iterator {
   		private int currentIndex;
   		@Override
   		public boolean hasNext() {
   			if(currentIndex < size){
   				return true;
   			}
   			return false;
   		}
   
   		@Override
   		public Object next() {
   			Node node = head;
   			for(int i=1;i<=currentIndex;i++){
   				node = node.getNext();
   			}
   			currentIndex++;
   			return node.getData();
   		}
   	}
   
   }

   public class Node {
   	private Object data;
   	private Node next;
   	
   	public Node(Object data, Node next) {
   		super();
   		this.data = data;
   		this.next = next;
   	}
   	public Object getData() {
   		return data;
   	}
   	public void setData(Object data) {
   		this.data = data;
   	}
   	public Node getNext() {
   		return next;
   	}
   	public void setNext(Node next) {
   		this.next = next;
   	}	
   }

    注意LinkedList的思想：head标示链表列的头部，tail标示最后一个节点，每当有节点加入时，将当前的tail的next指向新节点，并将新节点作为新的tail

   

4. 定义实体类

   public class Cat {
   	private int id;
   
   	public Cat(int id) {
   		super();
   		this.id = id;
   	}
   
   	@Override
   	public String toString() {
   		return "Cat: id=" +id;
   	}
   	
   }
   

    
5. 定义测试类，对ArrayList进行操作和LinkedList

   public class Test {
   
   	/**
   	 * @param args
   	 */
   	public static void main(String[] args) {
   		ArrayList<Cat> catList = new ArrayList<Cat>();
   		
   		
   		//LinkedList catList = new LinkedList<Cat>();
   		for(int i=1; i<=15; i++){
   			catList.add(new Cat(i));
   		}
   		System.out.println(catList.size());
   		Iterator iter = catList.iterator();
   		while(iter.hasNext()){
   			System.out.println(iter.next());
   		}
   	}
   
   }