Question

I have an interface I that is implemented by a base class B. The base class is extended by a bunch of classes (A,C,D) that must init some of the protected vars declared in base class B. I’d like to make the declaration of a constructor mandatory in the subclasses (A,C,D), to discourage the user from relying on default constructor that’s declared in B. Yet I do want the B’s default constructor to execute automatically, since B can be used by itself as well. How can I accomplish this?

thanks

Answer 1

Use an abstract superclass of B with a private constructor:

public abstract class BSuper {

    private BSuper() {
        // initialize stuff
    }

    protected BSuper(some params) {
        this():
        // other init with parms
    }
}


public class B extends BSuper {

     public B(some other params) {
         super(some params);
     }
}


public class A extends B {

     public A() {
         super(some other params);
     }
}

or similar