I'm writing Kotlin code, but I would like to see how it would look like in Java to see how much lines I'm saving.

Tools>Kotlin plugin>show bytecode

That does not really tell you how much LoC you save because the Java code it translates to and the code you would write yourself a trip very different things. Especially when you use concepts from kotlin that do not exist in Java

Not really what I was looking, but that's great as well. I talked to Hadi Hariri on Twitter and he said, that what I saw during conference was just two separate files