Iterator设计模式

Iteraotr设计模式是在集合中使用的非常多的一种模式，Iterator为我们提供了统一的遍历集合的方法，不管该种集合的底层是用数组还是链表实现。现在使用Iterator这种设计模式设计自己的集合类型，为了大家方便理解，现将我自定义的集合名和jdk中提供的集合名保持一致。

下面来写一个简单的Iterator设计模式的例子

1、定义Iterator接口(注意是自定义的，而非jdk自带的)

public interface Iterator{//判断是否还有下一个元素boolean hasNext();//取得下一个元素Object next();//获得迭代器Iterator iterator();}

2、定义Collection接口，该接口继承Iteraotr接口

 

public interface Collection extends Iterator{//增加元素public void add(Object obj);//获得列表大小public int size();}

3、定义ArrayList类，该类实现了Collection接口

public class ArrayList implements Collection{private Object[]objects=new Object[10];private int length=-1;private int current=-1;//添加元素public void add(Object obj){if(length<objects.length-1){objects[++length]=obj;}else{Object[]newobjects=new Object[objects.length+10];System.arraycopy(objects, 0, newobjects, 0, objects.length);objects=newobjects;this.add(obj);}}//获得指定位置的元素public Object get(int index){if(index<=length && index>=0){return objects[index];}else{ throw new  ArrayIndexOutOfBoundsException();}}//获得集合的大小public int size(){return length+1;}//判断是否有下一个元素@Overridepublic boolean hasNext(){// TODO Auto-generated method stubif(current<length)return true;return false;}@Overridepublic Object next(){// TODO Auto-generated method stubreturn objects[++current];}//返回迭代器public Iterator iterator(){return this;}}

4、定义LinkedList类，该类实现了Collection接口，并定义了一个节点类Node

public class Node{private Object object;private Node next;public Object getObject(){return object;}public void setObject(Object object){this.object = object;}public Node getNext(){return next;}public void setNext(Node next){this.next = next;}public Node(Object obj,Node node){this.object=obj;this.next=node;}}

 

public class LinkedList implements Collection{private Node head=null;private Node tail=null;private Node now;private int current;private int length=0;public void add(Object obj){Node node=new Node(obj,null);if(head==null){head=node;tail=head;now=head;}else{tail.setNext(node);tail=node;}length++;}public int size(){return length;}@Overridepublic boolean hasNext(){// TODO Auto-generated method stubif(current<length){return true;}else{return false;}}@Overridepublic Object next(){// TODO Auto-generated method stubObject obj=now.getObject();now=now.getNext();current++;return obj;}public Iterator iterator(){return this;}}

5、测试

public class Test{public static void main(String[] args){//Collection col=new ArrayList();Collection col=new LinkedList();for(int i=0;i<10;i++){col.add(i);}Iterator iter=col.iterator();while(iter.hasNext()){System.out.println(iter.next());}}}

6、总结

通过使用Iterator,使得我们遍历任何集合的代码都一样，从而提高了代码的重用性和简易性。