@hj @xianc78 @lanodan C# did add a lot of nice stuff to its language that Java is still missing or has bolted on. .NET also breaks comparability instead of keeping ancient shit in. (which Java finally did with 9 ~ 11, which breaks everything so no one uses them)
That said, I've written Mono/.NET code with Gtk# in the past and it's all pretty much dead and unsupported now. I'm not even sure if Gtk# works with .NET Core.
Java isn't a great language, but it was a major step away from manual memory management and a full VM. There are a lot of much better languages that run on the JVM such as Scala, Kotlin, etc. (although Scala libraries are getting pretty insane with cryptic functionality and error messages).