设计模式之迭代器模式（代码）

下面是模拟java里面的ArrayList和LinkedList的迭代器的实现原理

(1)首先创建一个集合类Collection

package com.alan.iterator;

public interface Collection {

	//添加元素
	void add(Object o) ;
	//得到长度
	int size() ;
	//得到迭代器
	Iterator iterator() ;
}

(2)创建迭代器接口Iterator

package com.alan.iterator;

public interface Iterator {

	//判断下一个有没有元素
	boolean hasNext() ;
	//得到下一个元素
	Object next() ;
}

(3)创建ArrayList类

package com.alan.iterator;

import java.util.Arrays;

public class ArrayList implements Collection{

	int DEFAULT_SIZE = 10 ;
	Object[] elementData ;
	int index ;
	
	public ArrayList(){
		elementData = new Object[DEFAULT_SIZE] ;
	}
	public ArrayList(int size){
		elementData = new Object[size] ;
	}
	@Override
	public void add(Object o) {
		//检查数组是否已满
		if(index>=elementData.length){
			//扩容
			ensureCapacity() ;
		}
		elementData[index] = o ;
		index++ ;
	}
	//给数组扩容
	public void ensureCapacity(){
		Object[] newContainer = new Object[elementData.length*2] ;//扩容为原来的两倍
		System.arraycopy(elementData, 0, newContainer, 0, elementData.length) ;
		elementData = new Object[newContainer.length] ;
		elementData = newContainer ;
	}
	
	@Override
	public Iterator iterator() {
		return new ArrayListIterator();
	}

	@Override
	public int size() {
		return 0;
	}
	
	private class ArrayListIterator implements Iterator{
		
		int cousor =0 ;
		@Override
		public boolean hasNext() {
			if(cousor <index){
				return true ;
			}
			return false;
		}

		@Override
		public Object next() {
			Object o = elementData[cousor] ;
			cousor++ ;
			return o;
		}
		
	}
}

(5)创建LinkedList类

package com.alan.iterator;

public class LinkedList implements Collection{
	
	private Node header ;
	private Node next ;
	
	private int index ;
	public LinkedList(){
		header = new Node(null) ;
	}
	
	@Override
	public void add(Object o) {
		// TODO Auto-generated method stub
		if(next ==null){
			next = new Node(o) ;
			header.next = next ;
		}else{
			Node node = new Node(o) ;
			next.next = node ;
			next = node ;
		}
		index++ ;
	}
	@Override
	public Iterator iterator() {
		// TODO Auto-generated method stub
		return new LinkedListIterator();
	}

	@Override
	public int size() {
		// TODO Auto-generated method stub
		return index;
	}
	
	private class LinkedListIterator implements Iterator{
		int cousor = 0 ;
		Node n ;
		@Override
		public boolean hasNext() {
			if(cousor <index){
				return true ;
			}
			return false;
		}

		@Override
		public Object next() {
			if(cousor == 0){
				n = header ;
			}
			n = n.next ;
			cousor++ ;
			return n.elementData;
		}
		
	}
	
	private class Node{
		Node next ;
		Object elementData ;
		
		public Node(Object elementData){
			this.elementData = elementData ;
		}
	}
}

(6)创建测试类Client

package com.alan.iterator;

public class Client {
	public static void main(String[] args) {
		
		//模拟LinkedList
		LinkedList list = new LinkedList() ;
		for(int i=0;i<10;i++){
			list.add(new Test(i)) ;
		}
		//模拟LinkedList的Iterator实现
		Iterator it = list.iterator() ;
		while(it.hasNext()){
			Object o = it.next() ;
			System.out.println("LinkedList:"+o);
		}
		//模拟ArrayList
		ArrayList arrayList = new ArrayList() ;
		for(int i=0;i<20;i++){
			arrayList.add(new Test(i)) ;
		}
		//便利arrayList
		Iterator arrayIt = arrayList.iterator() ;
		while(arrayIt.hasNext()){
			Object o = arrayIt.next() ;
			System.out.println("ArrayList:"+o);
		}
	}
	
	
}
class Test{
	int id ;
	public Test(int id){
		this.id = id ;
	}
	@Override
	public String toString(){
		return "obj:"+id+"  " ;
	}
	
}

输出的结果：

LinkedList:obj:0  
LinkedList:obj:1  
LinkedList:obj:2  
LinkedList:obj:3  
LinkedList:obj:4  
LinkedList:obj:5  
LinkedList:obj:6  
LinkedList:obj:7  
LinkedList:obj:8  
LinkedList:obj:9  
ArrayList:obj:0  
ArrayList:obj:1  
ArrayList:obj:2  
ArrayList:obj:3  
ArrayList:obj:4  
ArrayList:obj:5  
ArrayList:obj:6  
ArrayList:obj:7  
ArrayList:obj:8  
ArrayList:obj:9  
ArrayList:obj:10  
ArrayList:obj:11  
ArrayList:obj:12  
ArrayList:obj:13  
ArrayList:obj:14  
ArrayList:obj:15  
ArrayList:obj:16  
ArrayList:obj:17  
ArrayList:obj:18  
ArrayList:obj:19