Java设计模式—迭代器(Iterator)

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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。