If you know Java, then you know C#, TypeScript and Dart. All of those languages are practically the same.

In my case, I know Java (sic) and C#, so I learned Dart in less than a week.

In fact, Dart is a KISS version of C#. Dart applies the concept of less is better.

Also, another cool feature of Dart is the null sound, it is way better than in Java, C# and in most languages. It forces to deal with nulls correctly and it rules.