迭代器模式

所谓Iterator模式，即是Iterator为不同的容器提供一个统一的访问方式。本文以java中的容器为例，模拟Iterator的原理。

1 定义一个容器Collection接口

public interface Collection {
 
  
 
    void add(Object obj);
 
  
 
    int size();
 
  
 
    Iterator iterator();
 
  
 
}

2 定义一个Iterator迭代器的接口

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

3 定义一个ArrayList，实现Collection接口，并写一个实现了Iterator接口的内部类

public class ArrayList implements Collection {
 
  
 
    Object[] objects = new Object[10];
 
  
 
    int index = 0;
 
  
 
    
 
  
 
    public void add(Object obj) {
 
  
 
       if(index == objects.length) {
 
  
 
           Object[] newObjects = new Object[objects.length * 2];
 
  
 
           System.arraycopy(objects, 0, newObjects, 0, objects.length);
 
  
 
           objects = newObjects;
 
  
 
       }
 
  
 
       objects[index] = obj;
 
  
 
       index ++;
 
  
 
    }
 
  
 
 
 
  
 
    public int size() {
 
  
 
       return index;
 
  
 
    }
 
  
 
 
 
  
 
    public Iteratoriterator() {
 
  
 
       return new ArrayListIterator();
 
  
 
    }
 
  
 
 
 
  
 
    private class ArrayListIterator implements Iterator {
 
  
 
       private int currentIndex = 0;
 
  
 
       
 
  
 
       @Override
 
  
 
       public boolean hasNext() {
 
  
 
           if(currentIndex >= index) {
 
  
 
              return false;
 
  
 
           } else {
 
  
 
              return true;
 
  
 
           }
 
  
 
       }
 
  
 
       
 
  
 
       @Override
 
  
 
       public Objectnext() {
 
  
 
           Object obj = objects[currentIndex];
 
  
 
           currentIndex ++;
 
  
 
           return obj;
 
  
 
       }
 
  
 
    }
 
  
 
}

4 编写测试程序类Test

public class Test {
 
  
 
    public static void main(String[] args) {
 
  
 
       Collection c = new ArrayList();
 
  
 
       for(int i = 0; i < 5; i++) {
 
  
 
           c.add("string " + i);
 
  
 
       }
 
  
 
       System.out.println(c.size());
 
  
 
       
 
  
 
       Iterator it = c.iterator();
 
  
 
       while(it.hasNext()) {
 
  
 
           Object obj = it.next();
 
  
 
           System.out.println(obj.toString() + " ");
 
  
 
       }
 
  
 
    }
 
  
 
}

运行结果：

5

string 0

string 1

string 2

string 3

string 4