The documentation for Kotlin is now located on the new site. This page is kept for historical reasons


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Welcome to Kotlin documentation page!

Disclaimer: this is not a language specification. Neither is it a complete reference manual. These documents are written to give you an impression of what kind of language Kotlin is. Some of the examples are somewhat speculative as the implementation of the compiler and library is currently in progress. Most of the details presented here are subject to change. Your feedback and suggestions are very welcome. You can write comments or file an issue in the issue tracker.

See our blog. Follow us on Twitter.

Try Kotlin Online!

With our web-based editor you can

  • Write code with syntax and error highlighting
  • Use code completion (experimental)
  • Study running examples
  • Solve problems of the Code Challenge

Introductory Video

For an introduction, check out the presentation slides and video from StrangeLoop 2011.
More presentations are available on the Talks and Publications page.

What is Kotlin?

"Project Kotlin" is the codename for a statically-typed JVM-targeted programming language developed by JetBrains and intended for industrial use.

Why a new language?

At JetBrains, we’ve been developing for the Java platform for a long time, and we know how good it is. On the other hand, we know that the Java programming language has certain limitations and problems that are either impossible or very hard to fix due to backward-compatibility issues. We know that Java is going to stand long, but we believe that the community can benefit from a new statically typed JVM-targeted language free of the legacy trouble and having the features so desperately wanted by the developers.

Design goals
Design goals

The main design goals behind this project are

See more here.

What does it look like?

Wiki Markup
fun main(args : Array<String>) {
  println("Hello, world!")

See more here and below.

Development status

The compiler is being developed alongside with an IntelliJ IDEA integration, so the users will get IDE support as soon as they get the compiler (first public version is planned for the end of 2011).

If you're interested in keeping track of the project status, you're welcome to subscribe to the Kotlin blog or to follow us on Twitter.

Read more

FAQ. See this page for the answers to the most common questions.

Check out some Examples to get an idea of what Kotlin is:

If you are a Java developer, you might be interested in

If you are familiar with Scala, check out Comparison to Scala.

If you got interested, take the Feature tour:

Check out the Grammar for a formal syntax description.