4.2.1 使用Nullable<T>的各个成员

        static void Display(Nullable<int> x)
        {
            Console.WriteLine("HasValue：{0}", x.HasValue);
            if (x.HasValue)
            {
                Console.WriteLine("Value：{0}", x.Value);
                Console.WriteLine("Explicit conversion：{0}", (int)x);
            }
            Console.WriteLine("GetValueOrDefault()：{0}", x.GetValueOrDefault());
            Console.WriteLine("GetValueOrDefalut(10)：{0}", x.GetValueOrDefault(10));
            Console.WriteLine("ToString()：\"{0}\"", x.ToString());
            Console.WriteLine("GetHashCode()：{0}", x.GetHashCode());
            Console.WriteLine();
        }

        static void Main(string[] args)
        {
            Nullable<int> x = 5;
            x = new Nullable<int>(5);
            Console.WriteLine("Instance with value:");
            Display(x);
            x = new Nullable<int>();
            Console.WriteLine("Instance without value:");
            Display(x);

            Console.ReadKey();
        }