Multiplatform Kotlin Hello World

This project demonstrates sharing runtime independent code between different Kotlin's runtimes (Java/Android/JavaScript). It uses Gradle build engine.

It uses new support for multiplatform modules with plugin kotlin-multiplatform.

• Multiplatform library guide

Applications are built using features available from Kotlin 1.2 regarding multiplatform modules - see this blog posts:

• Kotlin 1.2 Released: Sharing Code between Platforms
• Webinar recording: Developing Multiplatform Projects in Kotlin 1.2

Older implementation that didn't use kotlin-multiplatform plugin and various hacks was moved to old-multiplatform branch. Oldest implementation that used various hacks was moved to old-multiplatform branch.

What is Kotlin?

otlin is a programming language developed by Jetbrains. It's fully compatibile with Java runtimes and also there is support for JavaScript transpilation. Experimental version of Kotlin/Native has goal to also build fully native apps for iOS, Linux, Windows and possibly other platforms.

What is it doing?

• writes Hello Kotlin!
• calculates first 1000 prime numbers (this part is shared between runtimes) and prints them

Structure

It's the Gradle multiple modules project.

• hello_android_app - Android application module, it's compiled to DEX bytecode, it produces APK file upon build
• hello_js_browser_app - application transpiled for frontend JavaScript, packed in WebPack, it's only statically served by Node.js
• hello_js_node_app - console application transpiled to Node.js JavaScript
• hello_jvm_app - console application compiled to Java bytecode for JVM, produces JAR that can be executed by eg. Oracle JVM
• hello_lib - multiplatform library project, with shared and platform specific code
  • commonMain - shared Kotlin source code, platform independent code
  • commonTest - shared tests, platform independent tests
  • jsMain - JavaScript runtimes platform dependent code
  • jsTest - JavaScript runtimes specific tests
  • jvmMain - Java runtime platform dependent code
  • jvmTest - Java runtime specific tests
  • androidMain - Android runtime platform dependent code
  • androidTest - Android runtime specific tests

Modules dependency

Platform implementation specifics

• prime number calculation is platform independent, single code shared for all platforms
• text output on screen is platform dependent
  • Android - it's done by adding with TextView to layout
  • Frontend JavaScript - it adds element in DOM of HTML page
  • Node.js JavaScript - uses console.log()
  • JVM - uses System.out.println()

Note: Ordinary console output can be done by println() function from Kotlin Standard Library.

Implementation in modules

Building and running the demo

It was checked only under Linux Mint, probably there won't be any problems with most Unix-like environments.

Android application

You can use Android Studio to run the application. To build from command line, you can use

# ./gradlew hello_android_app:build

and APK file is located in your build/outputs/apk directory.

JVM console application

# ./gradlew hello_jvm_app:build

You can than run the JAR file using java -jar hello_jvm_app.jar command from build/libs directory.

Frontend JavaScript application

# ./gradlew hello_js_browser_app:build

Webpack allows to host site directly from Gradle by

# ./gradlew hello_js_browser_app:run 

It will run locally on http://localhost:8088/.

Node.js console application

# ./gradlew hello_js_node_app:build

You can execute it in hello_js_node_app directory by:

# node ./app.js

to see all build options

# ./gradlew tasks --all

License

Do whathever you want with this.