C#字符串默认值

 using System;
 class MYTestX
 {
     class CT
     {
     }
     class CO
     {
         public CT ott;  //默认是null
         public string strx;//默认也是null，而不是空串""
         public virtual void Test()
         {
             Console.WriteLine("co-testJ");
         }
     }
     static void Main(string[] args)
     {
         CO oo = new CO();
         CO ot = null;
 
         Console.WriteLine(oo.strx + "ttt");
         Console.WriteLine(null + "ttt"); //null可以与字符串连接，不会出现异常
     }
 }