From the menu select Code
| Convert Java File to Kotlin File
and kaboom! Your task is done. Your first Kotlin activity is ready. As a means of verifying everything is fine, we suggest you run the project once. If you can see Hello World on the emulator or device that means you have successfully configured Kotlin for Android.
Or, create a new Kotlin file (File | New | Kotlin File/Class), and then paste your Java code into that file, when prompted, click Yes to convert the code to Kotlin. You can check Don't show this dialog next time, which makes it easy to dump Java code snippets into your Kotlin files:
Have a watchful eye on such conversion that IDE is doing for you. With great power comes great responsibility ...
