Thank you for bringing this to my attention, my current project is on Java 11, and I'm really struggling with the restrictions around enums (the poor man's sum

Thank you for bringing this to my attention, my current project is on Java 11, and I'm really struggling with the restrictions around enums (the poor man's sum type :)) and interfaces... maybe I can push for Java 17 at least! The fundamental problem in Java is, however, what you stated in your last sentence: you are limited in abstraction, in most cases you have to implement the specifics.