Knowing only Kotlin you seriously reduce the number of seats that can be arranged. It's a bad career strategy.
Aylin.Von answered on April 7th 20 at 10:46
The problem is that you're not a developer, and has chosen you to teach.
With this approach in principle can not be.
Specialization between Java and Kotlin should be selected when you are at least sure just here and there.
laurine_Pacoc answered on April 7th 20 at 10:48
Just like Kotlin it and learn. The architecture of the system, components used, and OOP principles, design patterns, the ecosystem as a whole.
With that knowledge you can easily and Java-write the application. They - the main tool of the developer. A large part of the study, together with the first JAP. A parallel process, and quite complex. I see no reason to complicate it with something that you don't like.