一段有意思的代码：

1 namespace TestHahaha 2 { 3     class Program 4     { 5         6         static void Main(string[] args) 7         { 8             A a = new A(); 9             a.Print();10         }11 12     }13 14     public class A15     {16         public B bObj = null;17 18         public A()19         {20             bObj = new B(this);21         }22 23         public void Print()24         {25             if (bObj == null)26                 Console.Write("bObj == null");27             else28                 Console.Write("bObj != null");29         }30 31         public void SetBNull()32         {33             bObj = null;34         }35     }36 37     public class B38     {39         public A aObj = null;40 41         public B(A a)42         {43             aObj = a;44             a.SetBNull();45         }46     }47 }

答案是：bObj != null;