java设计模式-Iterator（迭代子）模式

   Iterator迭代子模式定义
    一般是对集合进行遍历使用，java的集合类都可以迭代，一般不需要自己设计Iterator

  

package iterator;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Test {

	public static void main(String[] args) {
		List<String> list = new ArrayList<String>();
		
		list.add("1");
		list.add("2");
		list.add("3");
		list.add("4");
		//获取List的迭代器
		Iterator<String> it = list.iterator();
		//迭代遍历List中的元素
		while(it.hasNext())
			System.out.println(it.next());
	}
}

    当然也可以自己设计迭代器，比如一个书架类，里面有个书本的数组属性，可以自己设计一个迭代器，对书架里面的书本进行迭代：

   

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;    
     }    
}   

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);    
     }