Question

I’m using this library and I’ve had to override some methods in a few super-classes. What I do now is extending the class I need and re-define the methods I need to override from it’s super-class.

class A { ... }

class B extends A { ... }

class C extends A { ... }

class myD extends B {

    protected void overriddenAfunction() { ... }

}

This obviously isn’t good when several classes extends the same super-class and I want all the sub-classes to use the same overriden methods (like if C would also need the same definition of overridenAFunction()).

Is there some design pattern or way to make this pretty? I’m imagining you could do something like this:

class A { ... }

class B extends A { ... }

class C extends A { ... }

class myD extends A {

    private A BorC = null;

    public myD(A BorC) {

        this.BorC = BorC;

    }

    protected void overriddenAfunction() { ... }

    public void overriddenBfunction() { 

        ((B) BorC).overriddenBfunction();

    }

    public void overriddenCfunction() { 

        ((C) BorC).overriddenCfunction();

    }

}

Usage:

A testB = new myD(new B());
A testC = new myD(new C());

However then I’d need to put in every method from B and C if it even works.

Is there a better way or workaround? All I want to do is avoid re-packaging the library though I guess it’s really the best solution?

I guess I could also make copies of B and C and have them extend myD while myD extends A. This library also have all the source-files available so I can do this or something similar.

Answer 1

There is no way to override A in a way that lets B and C benefit from the new functionality. You only have two options that I can see, and you mention them both:

• Rewrite A and repackage the library
• Let MyD extend A, and then Make copies of B and C that extend MyD instead.