[a_humean]

Except notably sum types and pattern matching are language features that are not assoicated with Java at all. They are more closely assoicated with ML and functional programming languages, and not with Java.

Java only got something approaching sum types in Java 17 with sealed classes, which came out in 2021.

Standard ML has had this feature since the 1980s!

You might want to consider that there are type system linages that exist that are quite different to the one presented by Java.