Or you can use both folders, this is entirely up to you. If you'd like, you can also rename the /src/main/java folder to /src/main/kotlin. With those changes to your library's adle, you can remove the automatically generated M圜lass.java file from your library's source folder ( /src/main/java/your/package/name), and start adding Kotlin files instead. This is assuming that you have a kotlin_version declared in your project level adle file, which is the usual way for Android projects, and I believe that's how Android Studio configures a project if you tick the checkbox to use Kotlin. Implementation ':kotlin-stdlib-jdk7:$kotlin_version' If you don't have the mavenCentral repository added for all modules in your project yet, you need to add that as well: apply plugin: 'java-library'

You need to add the Kotlin plugin and standard library. Implementation fileTree(dir: 'libs', include: )

The adle file you get when you create your module is something like this: apply plugin: 'java-library' Then browse to the starter directory in the downloaded materials and click Open. For all platforms, you might also want to check out ktor client or http4k which are both good libraries. Open the starter project in Android Studio 3.1.2 or greater by selecting Open an existing Android Studio project from the Welcome to Android Studio window: You can also use File Open in Android Studio. From there, you just need to enable Kotlin inside this module. For Android, Volley is a good place to get started.

You need a module with no Android dependencies and resources - this is what a Java library module does, so you start by creating one of those.

Android studio kotlin