学步园

 Java设计模式—迭代器(Iterator)

转自（http://blog.163.com/nonoliuhao@126/blog/static/1716520942010101131346478/）

1.Aggregate接口所声明的方法只有iterator方法一个，这是为了建立一个对对应聚合的 iterator

Java代码

1. package com.pattern.iterator; 
2.  
3. publicinterface Aggregate { 
4.     publicabstract Iterator iterator(); 
5. } 

package com.pattern.iterator;

public interface Aggregate {
	public abstract Iterator iterator();
}

2.iterator接口，执行元素递增，具有类似循环变量的功能。

Java代码

1. package com.pattern.iterator; 
2. publicinterface Iterator { 
3.     publicabstractboolean hasNext(); 
4.     publicabstract Object next(); 
5. } 

package com.pattern.iterator;
public interface Iterator {
	public abstract boolean hasNext();
	public abstract Object next();
}

3. 书籍类

Java代码

1. package com.pattern.iterator; 
2. publicclass Book { 
3.     private String name=""; 
4.  
5.     public Book(String name) { 
6.         this.name = name; 
7.     } 
8.      
9.     /**
10.      * 获得书籍名称
11.      * @return String
12.      */ 
13.     public String getName() { 
14.         return name; 
15.     } 
16. } 

package com.pattern.iterator;
public class Book {
	private String name="";

	public Book(String name) {
		this.name = name;
	}
	
	/**
	 * 获得书籍名称
	 * @return String
	 */
	public String getName() {
		return name;
	}
}

4.书架类

Java代码

1. package com.pattern.iterator; 
2. /**
3. * 书架类
4. * @author administrator
5. */ 
6. publicclass BookShelf implements Aggregate{ 
7.     private Book[] books; 
8.     privateint last = 0; 
9.      
10.     public BookShelf(int maxSize) { 
11.         this.books = new Book[maxSize]; 
12.     } 
13.      
14.     public Book getBookAt(int index) { 
15.         return books[index]; 
16.     } 
17.      
18.     //添加书籍 
19.     publicvoid appendBook(Book book) { 
20.         this.books[last] = book; 
21.         last++; 
22.     } 
23.     //获得书架存书的数量 
24.     publicint getLength() { 
25.         return books.length; 
26.     } 
27.                 //获得书架迭代器对象 
28.     public Iterator iterator() { 
29.         returnnew BookShelfIterator(this); 
30.     } 
31.      
32. } 

package com.pattern.iterator;
/**
 * 书架类
 * @author administrator
 */
public class BookShelf implements Aggregate{
	private Book[] books;
	private int last = 0;
	
	public BookShelf(int maxSize) {
		this.books = new Book[maxSize];
	}
	
	public Book getBookAt(int index) {
		return books[index];
	}
	
	//添加书籍
	public void appendBook(Book book) {
		this.books[last] = book;
		last++;
	}
	//获得书架存书的数量
	public int getLength() {
		return books.length;
	}
                //获得书架迭代器对象
	public Iterator iterator() {
		return new BookShelfIterator(this);
	}
	
}

5.书架迭代器类

Java代码

1. package com.pattern.iterator; 
2. publicclass BookShelfIterator implements Iterator{ 
3.     private BookShelf bookShelf; 
4.     privateint index; 
5.      
6.     public BookShelfIterator(BookShelf bookShelf) { 
7.         this.bookShelf = bookShelf; 
8.         this.index = 0; 
9.     } 
10.      
11.     //检查是否还有下一本书 
12.     publicboolean hasNext() { 
13.         if(index < bookShelf.getLength()) { 
14.             returntrue; 
15.         } 
16.         else { 
17.             returnfalse; 
18.         } 
19.     } 
20.     //返回指定位置的书籍 
21.     public Object next() { 
22.         Book book = bookShelf.getBookAt(index); 
23.         index ++; 
24.         return book; 
25.     } 
26. } 

package com.pattern.iterator;
public class BookShelfIterator implements Iterator{
	private BookShelf bookShelf;
	private int index;
	
	public BookShelfIterator(BookShelf bookShelf) {
		this.bookShelf = bookShelf;
		this.index = 0;
	}
	
	//检查是否还有下一本书
	public boolean hasNext() {
		if(index < bookShelf.getLength()) {
			return true;
		}
		else {
			return false;
		}
	}
	//返回指定位置的书籍
	public Object next() {
		Book book = bookShelf.getBookAt(index);
		index ++;
		return book;
	}
}

6.测试类

Java代码

1. package com.pattern.iterator; 
2.  
3. publicclass Main { 
4.     publicstaticvoid main(String[] args) { 
5.         //生成一个书架 
6.         BookShelf bookShelf = new BookShelf(4); 
7.         //向书架添加书籍 
8.         bookShelf.appendBook(new Book("周恩来的晚年岁月")); 
9.         bookShelf.appendBook(new Book("C++网络编程")); 
10.         bookShelf.appendBook(new Book("J2EE网络编程精解")); 
11.         bookShelf.appendBook(new Book("Java编程思想")); 
12.          
13.         //获得书架迭代器 
14.         Iterator it = bookShelf.iterator(); 
15.         while(it.hasNext()) { 
16.             Book book = (Book)it.next(); 
17.             System.out.println(book.getName()); 
18.         } 
19.     } 
20. } 

package com.pattern.iterator;

public class Main {
	public static void main(String[] args) {
		//生成一个书架
		BookShelf bookShelf = new BookShelf(4);
		//向书架添加书籍
		bookShelf.appendBook(new Book("周恩来的晚年岁月"));
		bookShelf.appendBook(new Book("C++网络编程"));
		bookShelf.appendBook(new Book("J2EE网络编程精解"));
		bookShelf.appendBook(new Book("Java编程思想"));
		
		//获得书架迭代器
		Iterator it = bookShelf.iterator();
		while(it.hasNext()) {
			Book book = (Book)it.next();
			System.out.println(book.getName());
		}
	}
}

输出结果:
周恩来的晚年岁月
C++网络编程 J2EE网络编程精解 Java编程思想
迭代器设计恩想：       迭代器可以顺序访问一个聚集中的元素而不必显露聚集的内部对象。多个对象聚在一起形成的总体称为聚集，聚集对象是能够包容一组对象的容器对象。迭代器模式将迭代逻辑封装到一个独立的对象中，从而与聚集本身隔开。迭代算法独立于聚集对象，修改迭代算法不会对聚集对象产生任何影响，实现程序的松耦合。