Can't get kotlin "hello world" example to Run in intelliJ

Question

I'm following the intelliJ IDEA tutorial titled Create your first Kotlin application (Last modified: 08 March 2021). Here are the various versions I'm using:

~$ java -version
java version "16" 2021-03-16
Java(TM) SE Runtime Environment (build 16+36-2231)
Java HotSpot(TM) 64-Bit Server VM (build 16+36-2231, mixed mode, sharing)

~$ javac -version
javac 16

---

Here's my code:

fun main(args: Array<String>) {
    println("What is your name?")
    val name = readLine()
    println("Hello $name")
}

Here's what my project structure looks like:

I notice that it says "Kotlin not configured" above my code, but when I go to Tools > Kotlin > Configure Kotlin in Project, I get

:

In the Event Log pane, I see this:

4/15/21
1:54 PM Download pre-built shared indexes
                Reduce the indexing time and CPU load with pre-built JDK shared indexes
                Always download
                Download once
                Don't show again
                Configure...

1:54 PM Gradle sync started

1:54 PM Gradle sync failed: Unsupported class file major version 60 (5 s 329 ms)

1:55 PM No IDE or plugin updates available

In the Problems(?) pane, I see this:

Unresolved reference: println
Unresolved reference: readLine
Unresolved reference: println
Parameter 'args' is never used
Package directive doesn't match file location

Any ideas on why the basic functions in my program are not recognized?

Thanks for looking!

Edit: I tried downloading JDK 15 and specifying that in my Project Structure, but I got the same results:

Answer 1

try build>clean project. As for your unresolved references, you can double-click/left-click > show context options. If that doesn't work then maybe reinstall InteliJ Idea or download Android Studio which has a lot more support on google and yt.

Answer 2

Okay, I got it working. I'll try to figure out what I did.

tldr; I had to switch from JDK 16 to JDK 15 to get my hello world console application to run.

First, when I was setting up the project, I chose the wrong Project Template: I selected JVM - Application rather than JVM - Console Application. This is what I needed to do:

So, I started a new project, chose the right template, and I typed in my code, and I noticed a Build pane at the bottom left displayed:

I tried Build > Build Project, and nothing changed. So, I tried the Run menu item: the first section of the Run menu was grayed out, but there was another Run command in the second section of the Run menu. I selected that Run, and a little window popped up with the following:

      Run
  0  Edit Configurations

The "0 Edit Configurations" line was highlighted, and I got nowhere trying to figure out how to Run my code.

So, I started yet another new project, and this time I selected a different JDK, version 15:

After clicking Next, then Finish, I typed in my code, and this time the Build pane looked like the following (without me doing anything but typing in my code):

After I finished typing in my code, as the tutorial described, this time there was a little green arrow in the gutter:

When I clicked on the green arrow in the gutter, I could successfully Run my program.

So, it appears that you cannot use JDK 16, and you have to use JDK 15. intelliJ was able to detect all my installed Java versions, so any version you have installed should appear as a choice in the the project settings. You may have to quit intelliJ, then restart intelliJ after you install JDK 15 in order to see it listed as a choice under Project JDK: when you create a project.