求助

各位大哥们，请问为什么
interface Itest
    {
        void f();
    }
    class class1 : Itest
    {
        public void f()
        {
            Console.WriteLine("class1");
        }

    }
    class class2 : class1
    {
      public void  f()
        {
            Console.WriteLine("class2");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Itest mytest = new class2();
            mytest.f();
            Console.Read();
        }
    }
结果会是class1啊？