How to run Kotlin function in Intellij Idea

Question

I have created a test project aiming to start with Kotlin in IntelliJ IDEA CE.

The IDE version and the system is 2017.1.4 Build #IC-171.4694.23, built on June 6, 2017 JRE: 1.8.0_112-release-736-b21 x86_64 JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o Mac OS X 10.12.4

There is one .kt file with a main function in it. When I right-click on it I can select Run, but I get an error form JUnit: !!! JUnit version 3.8 or later expected.

I figured out it was about missing configuration, but I can't set up a proper one for Kotlin as well. Namely it requires a 'main class', which I don't have. Setting package name instead, as some other discussions suggest didn't help either.

What is the proper configuration for Kotlin in IDEA?

Thanks!

Could you show the class definition including the main function? Maybe there is a mistake in the main function, e.g. not public or static? — Maarten Bodewes
– Maarten Bodewes, Commented Jun 18, 2017 at 13:02
Yes, it was my mistake, I declared args: String instead of args: Array<String> — Bord81
– Bord81, Commented Jun 18, 2017 at 13:07

frin · Accepted Answer · 2019-02-16 18:11:58Z

32

I had a problem where I could not even run the code, IntelliJ IDEA offered me to create a new configuration.

I solved the problem by marking the "src" folder as "Sources" in Project Structure (File > Project Structure, select src and mark it as Sources). For some reason generating new project didn't mark src folder as sources automatically.

Once I did that an arrow appeared next to the main function and I could run it.

answered Feb 16, 2019 at 18:11

frin

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3 Comments

IgorGanapolsky Over a year ago

There is no such option as you described

frin Over a year ago

@IgorGanapolsky did you check under the Modules tab in Project Structure window? You should see a file tree on the right, and "Mark as" options above it.

user118967 Over a year ago

Perfect answer, that's all I need to know. Silly of IntelliJ IDEA to require this.

Kamafeather · Accepted Answer · 2021-12-27 00:06:21Z

18

Check that your IDEA is up to date. When creating a new Project you can select Kotlin like this:

This will automatically configure Kotlin for you. If you started a Java project and want Kotlin support, there will be a little window in the bottom right corner to configure Kotlin in the project for you. (not needed if the project is created like shown above)

There you want to select Java, not Javascript and after that click on "Configure '...' module in '...' project as Kotlin (Java) module..."

When your project is set up correctly, make sure that your main function is called "main" and has a parameter of type Array<String>.

fun main(args: Array<String>) {

}

Next to it a Kotlin "K" will appear, which you can click on to run your main function.

edited Dec 27, 2021 at 0:06

Kamafeather

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answered Jun 18, 2017 at 13:10

creativecreatorormaybenot

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4 Comments

sednanre Over a year ago

It's also a good thing to check if you by any chance put a class Main {at the file (like we do in java), for example. I had that in my file and it wasn't running. After taking it off, the method main was recognized and I could run it.

user9347168 Over a year ago

For me, this doesn't work at all. I've created a new Kotlin project from scratch, but there is no way to run the class and the main method.

IgorGanapolsky Over a year ago

There is no Kotlin (JVM) option for new projects

Tobias Reich Over a year ago

These days if you click "New Project" you can choose whether Java, Kotlin, JS etc

Big Pumpkin · Accepted Answer · 2019-09-03 21:22:21Z

18

Coming from a Java background, I instinctively put the main function inside a class. Then IntelliJ wouldn't let me run it. After taking the main function out of class to the top level, IntelliJ automatically put the green arrow next to the main function and added Run to the context menu (brought up by right clicking the file).

answered Sep 3, 2019 at 21:22

Big Pumpkin

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2 Comments

IgorGanapolsky Over a year ago

Kotlin doesn't require classes

user4367461 Over a year ago

I had this issue too. Thanks

Tawhid Monowar · Accepted Answer · 2024-08-27 17:09:04Z

2

Step-1: Go to: Main Menu -> Project Structure -> Modules
Step-2: Mark "src" folder as "Sources"

answered Aug 27, 2024 at 17:09

Tawhid Monowar

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Comments

Bord81 · Accepted Answer · 2017-06-18 13:11:53Z

1

Update: It works, I just had to put correct arguments args: Array<String>

edited Jun 18, 2017 at 13:11

answered Jun 18, 2017 at 13:09

Bord81

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1 Comment

IgorGanapolsky Over a year ago

Not needed for newer versions of Kotiln: kotlinlang.org/docs/tutorials/kotlin-for-py/hello-world.html

Bohemian · Accepted Answer · 2024-10-22 20:49:15Z

0

The only thing that worked for me was to install the Kotest plugin.

answered Oct 22, 2024 at 20:49

Bohemian♦

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