Creating Any Data Types in Dart and Flutter

As we know, all programming languages have some data types. I've been learning dart and as I didn't code much in C or Java, I am not that much familiar with how these actually works.

It has some basic data types like
String
int
bool
etc etc

But, this moring I was working on Stateful Widget in Flutter and I saw this kind of code

class MyApp extends StatefulWidget
{
  @override
  _myState createState() => _myState();
} 

class _myState extends State<MyApp> {
    ...
}

_myState createState() => _myState();

But I couldn't understand. As far as I knew, we use data type beofre a variable or class name [in this case its return type].
So, I dig into this and found that we can create any types. The real thing is when we create _myState  Class, it becomes a type.
That's the reason we can use it as type later.

Actually, all types are just types. Even primitive data types like String and int are just classes that are defined in the dart libraries

To see the full discussion: Stack OverFlow