public override DataListBase Next()
        {
            DataListBase data = categoryInfo.GetData(index);

            index++;
            return(data);
        }
        public override DataListBase Next()
        {
            DataListBase data = userInfo.GetData(index);

            Console.WriteLine("Iterator class index: {0}", index);
            index++;
            return(data);
        }
        public override DataListBase Next()
        {
            DataListBase data = bookInfo.GetData(index);

            return(data);
        }