Parent可以调用Child Class方法吗？

Question

Referring here

A is a precompiled Java class (I also have the source file) B is a Java class that I am authoring
B extends A.

How can logic be implemented such that A can call the methods that B has.
The following are the conditions:

• I don't want to touch A(only as a last option though that is if no other solution exists).
• I don't want to use reflection.

As stated, if needed I could modify A. What could be the possible solution either way?

Answer 1

Class A should define the methods it's going to call (probably as abstract ones, and A should be an abstract class, per Paul Haahr's excellent guide ); B can (in fact to be concrete MUST, if the method are abstract) override those methods. Now, calls to those methods from other methods in A , when happening in an instance of class B, go to B's overrides.

The overall design pattern is known as Template Method ; the methods to be overridden are often called "hook methods", and the method performing the calls, the "organizing method".

Answer 2

Yes it seems that if you override the super/base-classes's functions, calls to those functions in the base class will go to the child/derived class. Seems like a bad design in my opinion, but there you go.

class Base
{
    public void foo()
    {
        doStuff();
    }
    public void doStuff()
    {
        print("base");
    }
}

class Derived extends Base
{
    @Override
    public void doStuff()
    {
        print("derived");
    }
}

new Derived().foo(); // Prints "derived".

Obviously all of Derived 's methods have to be already defined in Base , but to do it otherwise (without introspection) would be logically impossible.

Answer 3

I would be rather hesitant to do this. Please correct me if I am wrong and then I will delete, but it sounds like you want to maintain an A object along with a B object. If they indeed are not the same object, the "tying together" (that's a scientific term) you'll have to do would be pretty ugly.