Java JAR Method Overriding

Question

So I'm new to Java and would really like some suggestions here.

I have a jar XYZ.jar which I've added to my classpath. This XYZ.jar has some 4 classes namely A,B,C,D. There is a method in CLASS D namely private void METHOD P() which is being called by CLASSES A,B,C.

Now I have a class Main.java in my project which is having a method METHOD R().

Now I would like to override private void METHOD P() with METHOD R() present in my Main.java. One thing I can do is that, I can extend my Main class with CLASS D. But, I would then have to modify the methodnames in CLASSES A,B,C which I don't want to do as the said classes are inside the jar.

So, what I would like to know is whether there's a way to override a private method of a class present inside a jar without making any changes to the rest of the classes calling the method, present inside the jar.

Answer 1

Assuming your classes A, B and C expect a class D as their construction parameter:

class Main extends D {
    public static void Main(String[] args) {
        Main main = new Main();
        A a = new A(main);
        B b = new B(main);
        C c = new C(main);
    }

    public void R() { ... }

    public void P() {
        R();
    }
}

But this only works if D and it's method P() are not final, and your other classes don't instantiate D themself.

Another but expensive way would be to use PowerMockito to mock your method D.P() to use your Main.R(). But this shouldn't be used for production code