kotlin-gradle-plugin is used to compile Kotlin code with Gradle. Basically, its version should correspond to the Kotlin version you want to use. E.g. if you want to use Kotlin 1.0.3, then you need to aplly kotlin-gradle-plugin version 1.0.3 too.

It's a good idea to externalize this version in gradle.properties (opens new window) or in ExtraPropertiesExtension (opens new window):

buildscript {
   ext.kotlin_version = '1.0.3'

   repositories {
     mavenCentral()
   }

   dependencies {
     classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
   }
}

Then you need to apply this plugin to your project. The way you do this differs when targeting different platforms:

Targeting JVM

apply plugin: 'kotlin'

Targeting Android

apply plugin: 'kotlin-android'

Targeting JS

apply plugin: 'kotlin2js'

These are the default paths:

• kotlin sources: src/main/kotlin
• java sources: src/main/java
• kotlin tests: src/test/kotlin
• java tests: src/test/java
• runtime resources: src/main/resources
• test resources: src/test/resources

You may need to configure SourceSets (opens new window) if you're using custom project layout.

Finally, you'll need to add Kotlin standard library dependency to your project:

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

If you want to use Kotlin Reflection you'll also need to add compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"

Android Studio can configure Kotlin automatically in an Android project.

Install the plugin

To install the Kotlin plugin, go to File > Settings > Editor > Plugins > Install JetBrains Plugin... > Kotlin > Install, then restart Android Studio when prompted.

Configure a project

Create an Android Studio project as normal, then press Ctrl + Shift + A. In the search box, type "Configure Kotlin in Project" and press Enter.

<img src="http://i.stack.imgur.com/w8LnT.png" alt="Dialog of "Configure Kotlin" search result" /> (opens new window)

Android Studio will alter your Gradle files to add all the necessary dependencies.

Converting Java

To convert your Java files to Kotlin files, press Ctrl + Shift + A and find "Convert Java File to Kotlin File". This will change the current file's extension to .kt and convert the code to Kotlin.

(opens new window)

Steps: