Inheritance of classes that implements interfaces

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C#

.NET

programming

Hello everybody.

I have this piece of code to explain my problem:

using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication1
{
    public interface Interface1
    {
        void Test();
    }
    public class BaseClass : Interface1
    {
        public void Test()
        {
            throw new NotImplementedException(); //Execution jumps here always. I need it to execute this line only if Class1 doesn't have a Test function.
        }
    }
    public class Class1 : BaseClass
    {
        public void Test()
        {
            return; //Why not here?
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Class1 a = new Class1();
            Object obj = a as Object;
            Interface1 itf = a as Interface1;
            itf.Test(); // <-- Why it calls BaseClass.Test() ?
        }
    }
}

When the program execution reaches the itf.Test() in the Main function I expect it would call the Class1.Test() function instead of the BaseClass.Test(). I need to execute the BaseClass.Test() method only if Class1.Test() function is not implemented. In that case the program would fire a NotImplementedException.
Anyone could help me please? Thanks.