static nested class

Nested classes that are static are called static nested classes. 
Nested class in different programming languages:
* Classes in C++ are merely nested type definitions, so only act as namespaces for nested type definitions. Nested class in C++ is essential static.
* Nested class in C# is static.
* In Kotlin, nested class is static by default; but we can use inner keyword to create an inner class in Kotlin.
* PHP, JavaScript, and TypeScript has no nested class, so also has no static nested class.