Statically typed programming language
for the JVM, Android and the browser
100% interoperable with Java™
Try Kotlin First glimpse of Kotlin 1.1 read more

Why Kotlin?

Concise

Create a POJO with getters, setters, equals(), hashCode(), toString() and copy() in a single line:

data class Customer(val name: String, val email: String, val company: String)

Or filter a list using a lambda expression:

val positiveNumbers = list.filter {it > 0}

Want a singleton? Create an object:

object ThisIsASingleton {
  val companyName: String = "JetBrains"
}

Safe

Get rid of those pesky NullPointerExceptions, you know, The Billion Dollar Mistake

var output : String
output = null

And of course, Kotlin protects you from mistakenly operating on nullable types, including those from Java

println(output.length())

And if you check a type is right, the compiler will auto-cast it for you

fun calculateTotal(obj: Any) {
  if (obj is Invoice) {
    obj.calculateTotal()
  }
}

Versatile

Multi-purpose language allowing you to build any type of application

Android Development.
No performance impact.
Very small runtime.

Application Server.
The technology doesn't matter. 100% compatible with all JVM frameworks.

JavaScript. Write code in Kotlin and target JavaScript to run on Node.js or in browser

Enterprise. Use Kotlin for any type of Enterprise Java EE development.

Web. Whether you want strongly typed HTML, CSS builders or just plain web development.

Interoperable

Create and consume Java code at will

import io.netty.channel.ChannelInboundMessageHandlerAdapter
import io.netty.channel.ChannelHandlerContext

public class NettyHandler: ChannelInboundMessageHandlerAdapter<Any>() {
  public override fun messageReceived(p0: ChannelHandlerContext?, p1: Any?) {
    throw UnsupportedOperationException()
  }
}

Or use any existing library on the JVM, as there’s 100% compatibility, including SAM support.

Target either the JVM or JavaScript. Write code in Kotlin and decide where you want to deploy to

import js.dom.html.*

fun onLoad() {
  window.document.body.innerHTML += "<br/>Hello, Kotlin!"
}

Tooling

A language needs tooling and at JetBrains, it’s what we do best!

Tooling

Tooling

Simplest Version
Name Reading
An “Object-oriented” Hello

What does it look like?

Concise, simple and very easy to read (and write)

package hello
Optional package header
fun main(args: Array<String>) {
Package-level function, which returns Unit and takes an Array of strings as a parameter
println("Hello World!") }
Have you noticed?
Semicolons are optional
More examples in the full language documentation
See Kotlin in action Getting Started with Kotlin in 2 minutes

Try Kotlin

1.0.3

In the browser

Try Online

Explore Kotlin code samples and solve problems directly in your browser.

Try Online
Standalone

Compiler

Compile your code from the command line or use build tools such as Ant, Gradle and Maven.

Download Compiler
Use

IntelliJ IDEA

Kotlin works with the free Community Edition, IntelliJ IDEA Ultimate or Android Studio.

Setup Plugin
Use

Eclipse

Get a preview version of the Kotlin plugin for Eclipse Luna.

Setup Plugin

Setting Up IntelliJ IDEA

Milestone Versions

A stable milestone version of Kotlin can be obtained from JetBrains Plugin Repository.
In IDEA navigate to: Settings -> Plugins -> Browse Repositories
Select the Kotlin plugin and then Download and Install.

Using the Kotlin Nightly Builds

In IDEA navigate to: Preferences -> Plugins -> Browse Repositories. Enter:

  • for IntelliJ IDEA 13 EAP:
    http://teamcity.jetbrains.com/guestAuth/repository/download/bt345/.lastSuccessful/updatePlugins.xml
  • for IntelliJ IDEA 12.1.5:
    http://teamcity.jetbrains.com/guestAuth/repository/download/bt345/.lastSuccessful/updatePlugins.xml?branch=idea12
  • for IntelliJ IDEA 12.1.4 and below: download manually, see instructions below.

Then you should be able to select the Kotlin plugin and Download and Install. The repository above contains nightly builds published automatically.

Who's using Kotlin

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