代码清单4-2 可空类型的装箱和拆箱行为 代码清单4-3 使用?修饰符来改写代码清单4-2

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Nullable<int> nullable = 5;
            object boxed = nullable;
            Console.WriteLine(boxed.GetType());
            int normal = (int)boxed;
            Console.WriteLine(normal);
            nullable = (Nullable<int>)boxed;
            Console.WriteLine(nullable);
            nullable = new Nullable<int>();
            boxed = nullable;
            Console.WriteLine(boxed == null);
            nullable = (Nullable<int>)boxed;
            Console.WriteLine(nullable.HasValue);
            Console.ReadKey();
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int? nullable = 5;
            object boxed = nullable;
            Console.WriteLine(boxed.GetType());
            int normal = (int)boxed;
            Console.WriteLine(normal);
            nullable = (int?)boxed;
            Console.WriteLine(nullable);
            nullable = new int?();
            boxed = nullable;
            Console.WriteLine(boxed == null);
            nullable = (int?)boxed;
            Console.WriteLine(nullable.HasValue);
            Console.ReadKey();
        }
    }
}