How to add Kotlin support for normal Java Lib in Android?

Question

When we want to use Kotlin in Android Studio, it's quite simple. Add the kotlin dependent library, and also add the Kotlin-Android plugin as below

 apply plugin: 'com.android.library'
 apply plugin: 'kotlin-android'

However, if I have a normal library (Used to be Java), and want to write in Kotlin, should I add any plugin? The below definitely not working.

 apply plugin: 'java-library'
 apply plugin: 'kotlin-android'

There is no 'kotlin-library' that I find to add in. What should I add to my module gradle to have it able to compile Kotlin?

Answer 1

You only need to add the Kotlin plugin:

apply plugin: "kotlin"

The java-library plugin was only recently added to Gradle and extends the java plugin. The naming does not expand to kotlin though.

Answer 2

As it been said you need to add

apply plugin: 'kotlin'

but you also need to add at least

compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version" 

to your dependency section of kotlin library module, otherwise standard library kotlin features would not work. E.g. you won't have @JvmStatic annotation, and so on.

The sample build.gradle of kotlin library module can look like this:

apply plugin: 'kotlin'

repositories {
    mavenCentral()
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
}

$kotlin_version should be defined in project build.gradle file.

The sample is taken from library project in Idea and tested to work with Android Studio project (tested with Android Studio 3.0 Beta 2) as a library dependency to an app module.