Is kotlin even worth learning as a Java developer?

Definitely! Since it is very similar to Java in a way, you'll learn it easy

Definitely fun for a side project, I wouldn't use it for anything official yet though

@TheBardAbaddon just a few hours back I read that Google is promoting Kotlin for android applications

It's worth to learn even if you won't use it in near future. In broadens your horizons.
You can choose Scala too ;-)

If you have a chance of switching your app to Kotlin and you learn Kotlin, it could only improve productivity by reducing null checks, removing redundant code, making your code more readable, giving you modern features like lambas/default args/100 other basic features.

Hint: you can convert only 1 file if you want. Don't have to go all the way. Fully compatible with existing Java code.

This question is stupid

@isaacWeisberg how's that?

@Sydochen well, I am sorry, that's just my opinion
But in fact a good programmer although has one golden tool with which he is master, it's better if you know how others tools are made of amd how to use them

Honestly it won’t be very useful unless it’s android. Simple as that.