官方文档： https://docs.microsoft.com/zh-cn/dotnet/csharp/programming-guide/classes-and-structs/static-classes-and-static-class-members
https://www.cnblogs.com/Matcha/p/5312268.html
https://www.jianshu.com/p/e1fee3558cb6
原文：https://www.cnblogs.com/fuyouchen/p/9419049.html