static void Main(string[] args)
        {
            IFactory factory = new UndergraduateFactory();// 只需要更换此处的代码即可
            // IFactory factory = new VolunteerFacroey();
            LeiFeng student = factory.CreateLeiFeng();

            student.BuyRice();
            student.Sweep();
            student.Wash();
        }
        public static LeiFeng CreateLeiFeng(string type)
        {
            LeiFeng result = null;

            switch (type)
            {
            case "学雷锋的大学生":
                result = new LeiFeng();
                break;

            case "志愿者":
                result = new Volunteer();
                break;

            default:
                break;
            }
            return(result);
        }