C# and new virtual methods. Many thanks to @kbatoev

interfaces.cs

public interface IInterface {
    int F();
}

public class A {
    public virtual int F() {
        return 7;
    }
}
var a = new A();
Console.WriteLine("######################################");
Console.WriteLine("((A) a).F() = {0}", ((A) a).F()); // 7

public class B : A, IInterface {
    public override int F() {
        return 8;
    }
}
var b = new B();
Console.WriteLine("######################################");
Console.WriteLine("((A) b).F() = {0}", ((A) b).F()); // 8
Console.WriteLine("((IInterface) b).F() = {0}", ((IInterface) b).F()); // 8

public class C : B, IInterface {
    public override int F() {
        return 9;
    }

    int IInterface.F() {
        return 100;
    }
}
var c = new C();
Console.WriteLine("######################################");
Console.WriteLine("((A) c).F() = {0}", ((A) c).F()); // 9
Console.WriteLine("c.F() = {0}", ((IInterface) c).F()); // 100


public class D : C {
    public new int F() {
        return -10;
    }
}
var d = new D();
Console.WriteLine("######################################");
Console.WriteLine("((A) d).F() = {0}", ((A) d).F()); // 9
Console.WriteLine("d.F() = {0}", d.F()); // -10
Console.WriteLine("((IInterface) d).F() = {0}", ((IInterface) d).F()); // 100

public class D1 : C, IInterface {
    public new int F() {
        return -11;
    }
}
var d1 = new D1();
Console.WriteLine("######################################");
Console.WriteLine("((IInterface) d1).F() = {0}", ((IInterface) d1).F()); // -10

// compile error because of ``override'' -- needed virtual keyword in class D 
// public class E : D {
//     public override int F() {
//         return -10;
//     }
// }

public class E : C {
    public new virtual int F() {
        return 10;
    }
}
var e = new E();
Console.WriteLine("######################################");
Console.WriteLine("((A) e).F() = {0}", ((A) e).F()); // 9
Console.WriteLine("e.F() = {0}", e.F()); // 10
Console.WriteLine("((IInterface) e).F() = {0}", ((IInterface) e).F()); // 100
Console.WriteLine("((IInterface) ((B) e)).F() = {0}", ((IInterface) ((B) e)).F()); // 100

public class G : E, IInterface {
    public override int F() {
        return 11;
    }
}
var g = new G();
Console.WriteLine("######################################");
Console.WriteLine("((A) g).F() = {0}", ((A) g).F()); // 9
Console.WriteLine("((IInterface) g).F() = {0}", ((IInterface) g).F()); // 11
Console.WriteLine("((E) g).F() = {0}", ((E) g).F()); // 11