Been in a weird position where I had to learn Java real fast, then learn Kotlin real fast to replace it. I find Java to be so incredibly unproductive compared to Kotlin, for all the reasons a sibling comment listed. I mean come on, default argument values and named input parameters are table stakes— it kills off the billion overloads, billion positional arguments, annd builder pattern nonsense all at once. Kotlin immutability by default is fantastic, I am 1000% behind default immutable data structures. The stupid, awful nullability madness disappears (mostly, need to train people to never use ! and !!). I appreciate Java, it got us to Kotlin, but Kotlin is ACTUALLY FUN to use, and expresses all ideas I have cleanly. Less, cleaner code just makes things easier to maintain, full stop.