所谓迭代器模式，就是把集合的数据和遍历分开

让遍历集合依赖于迭代器，而不依赖于具体的集合

从而可以达到代码复用

java中的增强for循环就是迭代器模式的应用，要使用增强for循环语法的集合，就要实现java.util.Iterator接口。

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在迭代器模式中，需要几个角色

• Iterator(迭代器)
• ConcreteIterator(具体的迭代器)
• Aggregate(集合)
• ConcreteAggregate(具体的集合)

它们的类图是这样的：

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下面用一个具体的例子来理解迭代器模式

 

用迭代器模式实现对书架的遍历

根据上面迭代器模式的类图，书架和迭代器需要以下：

Book	书的类
BookShelf	书架的类
BookShelfIterator	书架的迭代器
Iterator	迭代器的接口
Aggregate	集合的接口

 

类图如下：

代码实现如下

书的类：

package cn.wsichao.iteratorPattern;

public class Book {
    private String name;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

集合接口：

package cn.wsichao.iteratorPattern;

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

迭代器接口：

package cn.wsichao.iteratorPattern;

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

书架类：

package cn.wsichao.iteratorPattern;

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];
    }

    public void appendBook(Book book){
        this.books[last] = book;
        last++;
    }

    public int getLength(){
        return last;
    }

    @Override
    public Iterator iterator() {
        return new BookShelfIterator(this);
    }
}

书架的迭代器类：

package cn.wsichao.iteratorPattern;

public class BookShelfIterator implements Iterator {
    private BookShelf bookShelf;
    private int index;

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

    @Override
    public boolean hasNext() {
        if(index < bookShelf.getLength()){
            return true;
        } else{
            return false;
        }
    }

    @Override
    public Object next() {
        Book book = bookShelf.getBookAt(index);
        index++;
        return book;
    }
}

最后测试一下：

package cn.wsichao.iteratorPattern;

public class main {
    public static void main(String[] args) {
        BookShelf bookShelf = new BookShelf(5);

        bookShelf.appendBook(new Book("java"));
        bookShelf.appendBook(new Book("c"));
        bookShelf.appendBook(new Book("C++"));
        bookShelf.appendBook(new Book("python"));

        Iterator iterator = bookShelf.iterator();
        while(iterator.hasNext()){
            Book book = (Book) iterator.next();
            System.out.println(book.getName());
        }
    }
}

结果：

java
c
C++
python

Process finished with exit code 0