设计模式之迭代器模式

Posted 2022-12-02 独孤九戒

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 stub
		Aggregate 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 stub
		IProject 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());