设计模式之迭代器模式（Iterator Pattern） Java实现

拼搏现实的明天。 2022-04-23 10:06 232阅读 0赞

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：

**![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0x1XzF1_size_16_color_FFFFFF_t_70][]**

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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：

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td>Book</td> 
   <td>书的类</td> 
  </tr> 
  <tr> 
   <td>BookShelf</td> 
   <td>书架的类</td> 
  </tr> 
  <tr> 
   <td>BookShelfIterator</td> 
   <td>书架的迭代器</td> 
  </tr> 
  <tr> 
   <td>Iterator</td> 
   <td>迭代器的接口</td> 
  </tr> 
  <tr> 
   <td>Aggregate</td> 
   <td>集合的接口</td> 
  </tr> 
 </tbody> 
</table>

类图如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0x1XzF1_size_16_color_FFFFFF_t_70 1][]

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

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