| Generally speaking, I highly advise against this path. You're going to end up picking up some Java With Guest languages (Kotlin, Scala, Clojure, Fennel, etc) you almost always end up learning the original Hosted language. Heck, most languages have an FFI that you'll end up using at some point for C interop because it's all C at the end But you've been coding for 24 years. You're experienced enough that you can ignore most of the differences and just go full Kotlin. Most commonly though, you'll need to know: 1. The type system. Your IDE will largely handle the Java interop but not knowing how the type system works will still bite you 2. How the class path works. A lot of issues can be avoided if you understand the build system on this level 3. Your build tool (Gradle, Maven, etc). Basically for the same reason as the class path If you can tolerate that, you're going to be fine with Kotlin. If you can't, well, good luck and Godspeed Note: this is setting aside Kotlin's ability to target C and JS, but those are more uncommon use cases. And obviously decoupled from Java |