Programmers familiar with the IntelliJ [1] Java IDE know the kind of work its creator, JetBrains, produces. However, in the course of their work, the IntelliJ developers struggled with some annoying Java characteristics. In their opinion, it would have been difficult to improve Java, so they simply created their own language. The idea was to retain compatibility with and build at least as fast as Java, remove old annoyances such as the irritating null pointer exceptions (NPEs), and be more flexible and have a more compact syntax than Java. The result was Kotlin [2] (see the sidebar "The Name").

Mixing Machine

Kotlin is designed as a general-purpose programming language that is especially suitable for large enterprise projects. JetBrains itself would like to facilitate the development of IntelliJ using Kotlin [3] (see the "Developer Environment" box). Kotlin adopts much of Java's syntax; thus, it is object oriented and statically typed and offers generics. The inventors also added elements of functional languages, such as higher order functions. Automatic type derivation and mixins help keep the syntax short and sweet.

The source code is converted by a compiler into Java bytecode, which in turn runs on any Java Virtual Machine (JVM). Kotlin can thus use Java libraries and vice versa: Java can also integrate Kotlin code. This means developers can continue to use popular and powerful Java frameworks such as Spring or Hibernate. The compiler now also generates JavaScript code on request; the results then run in any browser. In February 2012, Kotlin and the reference implementation of the compiler were released under the Apache 2.0 license.

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