How to do it...

Let's go through these steps, with which we can create a self-executable JAR:

1. We’ll create a simple class HelloWorld.kt having the main function, which just prints out “Hello world!”:

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

1. Now we need to configure a jar task, which Gradle build goes through to inform it of our entry to our project. In a Java project, this will be the path to the class where our main() function resides, so you will need to add this jar task in build.gradle:

jar {
   manifest {
       attributes 'Main-Class': 'HelloWorldKt'
   }
   from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
}

1. After adding the preceding snippet to build.gradle, you need to run the following gradle command to create the jar file:

./gradlew clean jar

1. The created jar file can be found in the build/libs folder. Now you can just run the java -jar demo.jar command to run the JAR file.

After you do that, you can see the output in the console: