1. Java is mentioned in their comparison table. They just don't use it much. 2. There is really no reason to include Java in the search for your preferred language, since Kotlin is strictly better along every relevant axis.

Kotlin is a few tweaks on top of Java, most of which aren't relevant anymore, and it's not strictly better in most ways other than saving a few keystrokes (and preference).

It's a little bit nicer to write but that's almost irrelevant.

It also comes with some runtime cruft.

In reality there is no Kotlin without Java, which means most projects end up a bit 'dual'; every single Kotlin project we've had (except Android) folded back onto Java. Even Scala wasn't worth it, though that's a different question.

I strongly disagree with Kotlin being strictly better than Java. It pretends to fix things that haven't been problems in Java for more than 10 years while introducing a layer of syntactic complexity that's completely unwarranted. It just thrives on hype and Android development.

Kotlin’s closed-by-default design choice makes it worse than Java, and thus not strictly better than Java. It’s premature optimization, and a design-up-front-influenced paranoia/fear of any extension in not-designed-for places. But when I write code, I prefer to keep it open to extension, and in practice, I found a lot of value in extending decently written code, that would not be possible with Kotlin without having to go back and modify things to be open.