Question

This is what I’m trying to do:

class A {
    void myMethod() {
        // execute A
    }
}

class B extends A {
    void myMethod() {
        // execute B
    }
}

class C extends B {
    void myMethod() {
        // execute C
        // execute myMethod in A, without touching myMethod in B OR both
    }
}

I’d like to do this conditionally, that is sometimes call what’s in myMethod inside B and other times not, but always call myMethod inside A.

By calling super.myMethod() in C I get myMethod of B, but I only want myMethod of A. Is that possible? I’ve heard of “virtual” things, but I don’t know how to use them… yet.

Answer 1

No, it is not possible in Java on purpose. Class B overrides and therefore hides the implementation of myMethod in A from further deriving classes. Allowing C to call myMethod of A would violate this encapsulation. Consider a case where B.myMethod performs some updates before internally calling A.myMethod which are important for the correct functionality of B. Without these updates, the contract of B could be violated. Therefore, it should not be possible to call A.myMethod in a derived class without calling B.myMethod.

Usually, your design is flawed if you want to do stuff like this.

Of course, you can do stuff like suggested by Dave in the comments: You can alter the implementation of B.myMethod to call A.myMethod. This is okay, because B retains the control over when to call A.myMethod. Therefore, it can take care that its contract is not violated.

Another idea is to factor out the behaviour you want from A into another method and call this one.