使用迭代器

Question

I have a very basic question in mind. An Iterator is an interface so to create an object we will need to create a class that implements Iterator and then create an object for the same. But when i saw the use of iterator it confused me as we are referencing an interface directly without having a class that implements it. for example :

HashMap map = new HashMap();
   map.put("1", "One");
   map.put("2", "Two");
   Iterator i = map.entrySet().iterator();

how come we have an object of an Interface!!

Answer 1

Iterator是一个接口，但是map.entrySet().iterator()返回一个实现Iterator接口的对象。

Answer 2

You'll get some implementation from that call. You just cannot assume more than the things that are enforced (and documented) be the iterator interface. Look for "anonymous inner class".