null unification : Nullable « Data Type « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. Data Type
3. Nullable

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Runtime.InteropServices;

public class MainClass
{
   public static void Main(){
        int? x1 = null;
        int? x2 = new int?();
        int? y1 = 55;
        int? y2 = new int?(55);

        Console.WriteLine("{0}...{1}...{2}...{3}", x1, x2, y1, y2);

        Console.WriteLine("x1 == null? {0}", x1 == null);
        object x1o = x1; 
        Console.WriteLine("x1o == null? {0}", x1o == null);

        Console.WriteLine("{0}...{1}", x1.GetType(), x1o.GetType());
   }

}

......55...55
x1 == null? True
x1o == null? True

Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an ob
ject.
   at MainClass.Main()