设计模式之迭代器模式

设计模式之迭代器模式

    迭代器模式(ITerator Parttern)是目前已经没落的一个设计模式，定义如下：Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.(它提供一种方法访问一个容器对象中的各个元素，而又不需要暴露该对象内部的细节)

通用类图

四个角色

1.Iterator抽象迭代器，抽象迭代器负责定义访问和遍历元素的接口，基本上有三个固定的方法：first()获取第一个元素，next()访问下一个元素，isDone()是否已经访问到底部；

2.ConcreteIterator具体迭代器，具体迭代器角色实现迭代器接口，完成容器元素的遍历；

3.Aggregate抽象容器，容器角色负责提供创建具体迭代器角色的接口，必然有一个类似createIterator()这样的方法；

4.ConcreteAggregate具体容器，具体容器实现容器接口定义的方法，创建出容纳迭代器的对象。

通用源码

抽象迭代器

public interface Iterator {public Object next();public boolean hasNext();public boolean remove();}

具体迭代器

public class ConcreteIterator implements Iterator{private Vector vector=new Vector();public int cursor=0;public ConcreteIterator(Vector _vector){this.vector=_vector;}public boolean hasNext(){if(this.cursor==this.vector.size()){return false;}else{return true;}}public Object next(){Object result=null;if(this.hasNext()){return this.vector.get(this.cursor++);}else{result=null;}return result;}public boolean remove(){this.vector.remove(this.cursor);return true;}}

抽象容器

public interface Aggregate {public void add(Object object);public void remove(Object object);public Iterator iterator();}

具体容器

public class ConcreteAggregate implements Aggregate{private Vector vector=new Vector();public void add(Object object){this.vector.add(object);}public Iterator iterator(){return new ConcreteIterator(this.vector);}public void remove(Object object){this.remove(object);}}

场景类

public class Client {public static void main(String[] args) {// TODO Auto-generated method stubAggregate agg=new ConcreteAggregate();agg.add("abc");agg.add("aaa");agg.add("1234");Iterator iterator=agg.iterator();while(iterator.hasNext()){System.out.println(iterator.next());}}}

例子：整理项目信息

项目信息接口

public interface IProject {public void add(String name,int num,int cost);public String getProjectInfo();public IProjectIterator iterator();}

项目信息

public class Project implements IProject{private ArrayList<IProject> projectList=new ArrayList<IProject>();private String name="";private int num=0;private int cost=0;public Project(){}public Project(String name,int num,int cost){this.name=name;this.num=num;this.cost=cost;}public void add(String name,int num,int cost){this.projectList.add(new Project(name,num,cost));}public String getProjectInfo(){String info="";info=info+"项目名称："+this.name;info=info+"\t项目人数："+this.num;info=info+"\t项目费用"+this.cost;return info;}public IProjectIterator iterator(){return new ProjectIterator(this.projectList);}}

项目迭代器接口

public interface IProjectIterator extends Iterator{}

项目迭代器

public class ProjectIterator implements IProjectIterator{private ArrayList<IProject> projectList=new ArrayList<IProject>();private int currentItem=0;public ProjectIterator(ArrayList<IProject> projectList){this.projectList=projectList;}public boolean hasNext(){boolean b=true;if(this.currentItem>=projectList.size()||this.projectList.get(this.currentItem)==null){b=false;}return b;}public IProject next(){return (IProject)this.projectList.get(this.currentItem++);}public void remove(){}}

客户端

public class Client {public static void main(String[] args) {// TODO Auto-generated method stubIProject project=new Project();project.add("星球大战项目", 10, 100000);project.add("扭转时空项目", 100, 1000000);project.add("超人改造项目", 1000, 1000000);for(int i=0;i<104;++i){project.add("第"+i+"个项目", i*5, i*10000);}IProjectIterator projectIterator=project.iterator();while(projectIterator.hasNext()){IProject p=(IProject)projectIterator.next();System.out.println(p.getProjectInfo());}}}