Kotlin

What is Kotlin?

Kotlin is a statically typed programming language developed by Jetbrains, the company behind some of the world's most popular IDEs like IntelliJ and Pycharm.

Kotlin serves as a replacement for Java and runs on the JVM. It has been in development since 2011 and version 1.0 was released in August 2016.

The developer community has embraced Kotlin to such an extent that Google announced first class support for the language for Android Development at Google I/O 2017.

Version

As of this writing, the latest stable release of Kotlin happens to be version 1.2.71

Installation

Before proceeding with the installation instructions for Kotlin, you need to make sure that you have set up JDK (Java Development Kit) set up on your system.

If you do not have JDK installed on your computer, head over to the Installation section on this link to learn how to set it up.

Kotlin works with JDK 1.6+ so make sure you get the correct version installed. Once you are done setting up JDK, proceed with the following steps.

  • IntelliJ IDEA

    The quickest way to get Kotlin running on your machine is using it alongside the IntelliJ IDEA IDE. This is the recommended IDE for Kotlin because of the tooling support that is provided by JetBrains. You can grab the Community Edition of IntelliJ from JetBrains.

Once you have installed IntelliJ, you can get started with your first project in Kotlin without any further configurations.

Create a New Project and make sure you select the Java Module. Select the Kotlin checkbox on that screen.

new project screen

Give your project a name and click Finish.

project name

You will now be taken to the main editor where you will see your project files organized in the following manner.

project structure

In order to verify your installation, create a new Kotlin file in the src folder and name it app (or anything else that suits you)

project structure

Once you have the file created, type out the following ceremonial Hello World code. Don't worry if it doesn't make sense right away, it will be dealt with in detail later on in the guide.

fun main (args: Array<String>) {
    println("Hello World!")
}

project structure

You can now run this program by either clicking on the Kotlin icon on the gutter (left side of your editor with line numbers)

hello world

If everything goes fine, you should see the message Hello World! in your Run window as shown below

run window

  • Eclipse

While IntelliJ is the recommended IDE for developing with Kotlin, it is definitely not the only option out there. Eclipse happens to be another popular IDE of choice among Java developers and Kotlin is supported by Eclipse as well.

After setting up the JDK on your system, follow the instructions below.

Download Eclipse Neon for your operating system and once you have successfully installed it on your system, download the Kotlin Plugin for Eclipse from the Eclipse Marketplace.

eclipse marketplace

NOTE: You can also do the same by going into Help -> Eclipse Marketplace and then search for Kotlin Plugin

Once, the plugin is installed you are pretty much done but it would be a good idea to take the IDE for a spin with a quick Hello World sample.

Create a new Kotlin Project by clicking on File -> New -> Kotlin Project

new kotlin project

An empty project will be created with a directory structure quite similar to a Java project. It would look something like this

empty kotlin project

Go ahead and create a new Kotlin file in the src folder

Once that is done go ahead and type out the following code. Don't worry if it does not make sense right now, it will be covered later in the guide.

fun main (args: Array<String>) {
    println("Hello World!")
}

eclipse hello world

Now that you are done typing out the Hello World code, go ahead and run it. To run the file, right-click anywhere inside the editor and click on Run As -> Kotlin Application

eclipse run app

If all goes well, the console window would open to show you the output.

eclipse run app

  • Using the standalone compiler on the terminal

    If you are someone who prefers doing things in a more manual way and do not want to tie yourself down to an editor/IDE you might wanna use the Kotlin compiler.

Downloading the compiler

With every release of Kotlin, JetBrains ship a standalone compiler which can be downloaded from the GitHub releases. Version 1.1.51 happens to be the latest at the time of this writing.


Manual Installation

Once you have downloaded the compiler you need to unzip it and proceed with the standard installation using the installation wizard. Adding the bin directory to the system path is an optional step. It contains the scripts that are necessary to compile and run Kotlin on Windows, Linux and macOS.


Installation via Homebrew

You can install the compiler on macOS using Homebrew which is a package manager for macOS. Launch the Terminal app and issue the following commands

$ brew update
$ brew install kotlin

Installation via SDKMAN!

Another simple way of installing the Kotlin compiler on macOS, Linux, Cygwin, FreeBSD and Solaris is by using SDKMAN!. Launch the terminal and issue the following commands

$ curl -s https://get.sdkman.io | bash

Follow the instructions on the screen and once SDKMAN! is setup, issue the following command inside terminal

$ sdk install kotlin

As with all previous installation options, it would be a good idea to test run the installation.

Open a text editor of your choice and write a basic Kotlin program given below

fun main(args: Array<String>) {
    println("Hello, World!")
}

Save this file with a .kt extension. You are now ready to compile it and see the results. To do so, issue the following command

$ kotlinc hello.kt -include-runtime -d hello.jar

the -d option tells the compiler what you want the output to be called. The -include-runtime option makes the resulting .jar file self-contained and runnable by including the Kotlin runtime library in it.

If there were no compilation errors, run the application using the following command

$ java -jar hello.jar

If all goes well, you should see Hello World! printed on your terminal screen

$ java -jar hello.jar       
Hello, World!

Congratulations you have successfully set up the Kotlin compiler and development environment on your system. We will cover all of the intricacies and fun parts of Kotlin in this guide, but you can get a headstart if you want by going to the Try Kotlin website and going through the exercises there.

Kotlin scripts

Yout can also put Kotlin code in file with extension .kts without main function and run it as a script. $ kotlinc -script hello.kts

Documentation

One of the greatest things about Kotlin is its comprehensive and well-structured documentation. Even if you are new to programming, you will find yourself right at home with the docs. They do a pretty amazing job at laying it all out in a well-structured manner. You can check out the official documentation at this link.


Contributing to the Guide

This open source guide is curated by thousands of contributors. You can help by researching, writing and updating these articles. It is an easy and fun way to get started with contributing to open source.