类图：

 

代码示例：

 

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

package iterator;public interface Iterator {    public boolean hasNext();    public Object next();}

package iterator;public abstract class BookShelfs {        public abstract void appendBook(Book book);        public abstract Book getBookAt(int index);        public abstract int getLength();        }

package iterator;/** * 具体的聚合器 */public class BookShelf extends BookShelfs implements Aggregate {        private Book[] books;    //标记目前书架上有多少书    private int last;        public BookShelf(int maxsize){        books = new Book[maxsize];        last = 0;    }        @Override    public Book getBookAt(int index){        return books[index];    }        @Override    public void appendBook(Book book){        /*实际上应该有一个最大容量的判断，如果超出了数组边界，会抛出越界异常        (就看这里是由编程者自己做处理还是让编译器抛异常，上层程序再来处理)        如果是类的开发者，应该是会选择让上层程序来处理        */        books[last]=book;        last++;    }        @Override    public int getLength(){        return last;    }        @Override    public Iterator iterator() {        //直接创建使用一个迭代器        return new BookShelfIterator(this);    }}

package iterator;import java.util.Vector;public class BookShelf2 extends BookShelfs implements Aggregate {        private Vector
     
       books;        public BookShelf2(){        books = new Vector
      
       ();    }        @Override    public void appendBook(Book book){        books.add(book);    }        @Override    public Book getBookAt(int index){        return books.get(index);    }        @Override    public int getLength() {        return books.size();    }            @Override    public Iterator iterator() {        return new BookShelfIterator(this);    }}
      
     

package iterator;public class BookShelfIterator implements Iterator {        private BookShelfs bookShelf;    //记录下当前迭代的位置    private int index;        public BookShelfIterator(BookShelfs bookShelf){        this.bookShelf = bookShelf;        index = 0;    }        @Override    public boolean hasNext() {        if(index

package iterator;public class Book {    private String name;    public Book(){}        public Book(String name){        this.name = name;    }        public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}

 

package iterator;public class Client {    public static void main(String[] args) {        //数组存储书籍        BookShelf myShelf = new BookShelf(10);        //以一种不同的组织方式组织书的书架(Vector存放书籍)        BookShelf2 otherShelf = new BookShelf2();                myShelf.appendBook(new Book("thinking in java"));        myShelf.appendBook(new Book("effective java"));        myShelf.appendBook(new Book("design patterns"));                otherShelf.appendBook(new Book("head first java"));        otherShelf.appendBook(new Book("head first design pattern"));                Iterator it = new BookShelfIterator(myShelf);        while(it.hasNext()){            Book b = (Book) it.next();            System.out.println(b.getName());        }                it = new BookShelfIterator(otherShelf);        while(it.hasNext()){            Book b = (Book) it.next();            System.out.println(b.getName());        }                                    }}

 

运行结果：

thinking in javaeffective javadesign patternshead first javahead first design pattern