“Start using Kotlin” guide for Android Developers

Hello, dear reader. I hope you heard about Kotlin — JVM Programming Language from JetBrains.

@JakeWharton published document about Kotlin this week and huge amount of developers now want to try Kotlin in their Android apps. Here is lightweight guide for beginners (Gradle + IDEA based IDE).

1. Create new branch in your VCS
2. Kotlin maintainers created Gradle plugin for Kotlin, let’s add it

Open root build.gradle and add Kotlin Gradle plugin as dependency to the buildscript.dependencies closure

I’m not using “+” in dependencies for build stability, Please visit http://search.maven.org or https://bintray.com to find newest versions of dependencies.

3. Now let’s apply Kotlin Gradle plugin to our Android app module

Open app’s build.gradle (usually -> app/build.gradle) and add to beginning

apply plugin: 'kotlin-android'

4. Kotlin provides Standard Library (STD) as jar package, so let’s add it to dependencies in app’s build.gradle

dependencies {
    // Kotlin STD Library
    compile 'org.jetbrains.kotlin:kotlin-stdlib:0.10.195'
}

5. Almost done, now we should declare Kotlin sources directory for Android Gradle Plugin, app’s build.gradle

android {
    sourceSets {
        main.java.srcDirs += 'src/main/kotlin'
    }
}

Final version of app’s build.gradle

6. The last thing before starting to code something in Kotlin is IDE Support, I hope you use Android Studio or IDEA, Kotlin maintainers (internal team in JetBrains) created IDEA plugin for Kotlin, so let’s install it

Open IDE (IDEA or Android Studio) -> Preferences -> Plugins -> Browse repositories -> Search: Kotlin -> Install Kotlin plugin from JetBrains -> Restard the IDE.

That’s all.

Now let’s code smthg in Kotlin.

1. Sync Gradle configuration in IDE
2. Create folder for Kotlin code : src/main/kotlin
3. Let’s add new package in src/main/kotlin -> “nice.is.kotlin” (Yoda)
4. New -> Kotlin file -> HelloKotlinOnAndroid.kt

And you can use it in your Java code:

import nice.is.kotlin.HelloKotlinOnAndroid
//
new HelloKotlinOnAndroid().yo(context, "Kotlin, you are running on Android!");

Or better to write everything you can in Kotlin.

What to read?

1. “Using Project Kotlin on Android” from @JakeWharton
2. Kotlin official website http://kotlinlang.org
3. Kotlin documentation http://kotlinlang.org/docs/reference/

Please read exactly in this order, you’ll understand Java’s problems, Kotlin’s solutions and see usage examples.