int s = 5; int? s_null; long t; long? t_null; t = s; //隐式转换 S -> T s = (int)t; //显示转换 T -> S s_null = s; //隐式转换 S -> S? s = (int)s_null; //显示转换 S? -> T t_null = s_null; //隐式转换 S? -> T? s_null = (int?)t_null; //显示转换 T? -> S? t_null = s; //隐式转换 S -> T? s = (int)t_null; //显示转换 T? -> S
原文：http://www.cnblogs.com/goodspeed/p/3815799.html