I learnt Kotlin by taking an Android app which I had written in Java, and gradually converting it i to Kotlin, this was just after 1.0. I'm a solo developer, a

I learnt Kotlin by taking an Android app which I had written in Java, and gradually converting it i to Kotlin, this was just after 1.0. I'm a solo developer, and I use K and J together on most codebases (about 10), and at this point I only ever create K files. Regarding interop, I think it's a valid claim that K is 100% J compatible. I think instead of arbitrarily mixing the two, maybe start with a single module, or with testing. I write a lot of JS, and have been planning on trying out Kotlin with JS, because at this point, taking a JS function and converting it to Kotlin results in code that's between 70-80% Kotlin (const to val, add return types, etc.) I'm personally convinced that Kotlin is a good language to learn if you know Java.