Java中的继承不符合我的预期

Question

I have the following class:

public class X {
    public void A() {
        B();
    }

    private static void B() {
        System.out.println("111111111");
    }
}

Now I have the following inherited class Z:

public class Z extends X {

    private static void B() {
        System.out.println("22222222");
    }
}

now if I do

Z myClass = new Z();
Z.A();

I will get: 111111111 as a result. (Also, eclipse tells me that B() in the inherited class is never called).

Why? And how can I run the inherited B method?

Answer 1

The B methods are static . When you call the method A it uses the implementation of class B (because that's where the method A is defined). Class B is not aware of the existence of class Z and cannot call a method of class Z .

Because the method is static, it's not overridden upon inheriting from B . Polymorphism only works with instances of a class. Static method does not play the polymorphism game and cannot be overridden.

Answer 2

Change access modifier of method from private static to protected

If you re-define base class non-static & non-private method in derived class, it's called overriding .

If you re-define base class static method in derived class, it's called method hiding or method shadowing .

You have done hiding rather overriding in your example.

Have a look at this SE Question

Answer 3

You're calling X's inherited A method, and this calls its private B method.

private methods and attributes are not inherited.

Answer 4

It looks like you are overriding method B() in class Z but method B() is not overridden here. Since B() is static so class A and class Z has there own method B(). Scope of all the Static methods and variables are class level not an object level.