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.
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.