Java设计模式—迭代器(Iterator)

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 package com.pattern.iterator;

publicinterface Aggregate {
publicabstract Iterator iterator();
}

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 package com.pattern.iterator;
publicinterface Iterator {
publicabstractboolean hasNext();
publicabstract Object next();
}

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

3. 书籍类
Java代码 package com.pattern.iterator;
publicclass Book {
private String name="";

public Book(String name) {
this.name = name;
}

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

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 package com.pattern.iterator;
/**
* 书架类
* @author administrator
*/
publicclass BookShelf implements Aggregate{
private Book[] books;
privateint last = 0;

public BookShelf(int maxSize) {
this.books = new Book[maxSize];
}

public Book getBookAt(int index) {
return books[index];
}

//添加书籍
publicvoid appendBook(Book book) {
this.books[last] = book;
last++;
}
//获得书架存书的数量
publicint getLength() {
return books.length;
}
//获得书架迭代器对象
public Iterator iterator() {
returnnew BookShelfIterator(this);
}

}

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 package com.pattern.iterator;
publicclass BookShelfIterator implements Iterator{
private BookShelf bookShelf;
privateint index;

public BookShelfIterator(BookShelf bookShelf) {
this.bookShelf = bookShelf;
this.index = 0;
}

//检查是否还有下一本书
publicboolean hasNext() {
if(index < bookShelf.getLength()) {
returntrue;
}
else {
returnfalse;
}
}
//返回指定位置的书籍
public Object next() {
Book book = bookShelf.getBookAt(index);
index ++;
return book;
}
}

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 package com.pattern.iterator;

publicclass Main {
publicstaticvoid 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());
}
}
}

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。