maximally specific

package ch.fhnw.claudemartin;

abstract class A implements B {
}

interface B {

    default Object abc(final Integer i) {
        System.out.println("Interface B");
        return 1;
    }
}

interface C {

    default Object abc(final Object i) {
        System.out.println("Interface C");
        return 2;
    }
}

public class Test extends A implements C {

    public static void main(final String[] args) {
        final Test t = new Test();
        t.abc("foo");
        t.abc(123);
    }
}