使用Java中的其他方法的子类 [英] Subclass with additional method in Java

问题描述

我在Java中有一个子类的问题。我有以下类：

I have a problem with a subclass in Java. I have the following class:

MainIterator implements Iterator{
   //... Methods from the interface Iterator

   public void foo(){
      //Do something...
   }
}

并在我的主类中调用：

Iterator i = new MainIterator();
i.foo();

这不起作用，因为Iterator没有实现函数 foo >。如何可以得到这个工作没有类型的 i ？ i 必须来自类型Iterator。

which does not work, because Iterator does not implement the function foo(). How is it possible to get this working without a typecast of i? i has to be from type Iterator.

推荐答案

MainIterator i = new MainIterator();

Java编译器只允许调用属于声明的类型的方法变量。如果你使用

The Java compiler only allows calling methods that belong to the declared type of the variable. If you use

Iterator i = new MainIterator();

你告诉编译器：我创建一个类型为MainIterator的Iterator实例，但是你不需要在其余代码中知道这一点。只需将此对象视为Iterator的实例。而且Iterator没有任何foo（）方法。

you're telling the compiler: I create an instance of Iterator which is of type MainIterator, but you don't need to know about that in the rest of the code. Just consider this object as an instance of Iterator. And Iterator doesn't have any foo() method.

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