Question

The problem:

base interface:

 IBase

descendants:

InterfaceA extends IBase<Interface1>

InterfaceB extends IBase<Interface2>

When I try:

InterfaceC extends InterfaceA, InterfaceB 

I receive compile error:

The interface IBase cannot be implemented more than once with different arguments

Does exist workaround?
Thanks.

Answer 1

This is not possible and it cannot be in Java, at least.
Think of the following scenario:

    interface Base<K> {
    K get();
}

interface A extends Base<String> {
    String get();
}

interface B extends Base<Integer> {
    Integer get();
}

interface AB extends A, B {
    ??
}

When you go try to implement AB, if it were possible, what type would the get() method return. In Java, two methods in a class cannot have the same name/args but different return types…. hence, this is forbidden.

If you actually need some functionality similar to what you would get should Java allow this, I would suggest the following:

    abstract class C {
    A a;
    B b;
    String aGet() {
        return a.get();
    }

    Integer bGet() {
        return b.get();
    }
}

Or, to keep generics:

abstract class C<K, T> {
    Base<K> a;
    Base<T> b;
    K getA() {
        return a.get();
    }

    T getB() {
        return b.get();
    }
}