Getting ready

You need an IDE (preferably IntelliJ or Android Studio), and you need to tell it where your Kotlin files are present. You can do so by specifying it in the build.gradle file by adding the following:

sourceSets {
   main.java.srcDirs += 'src/main/kotlin/'
}

The preceding lines are required if you have your Kotlin files separated from Java packages. This is optional, and you can continue working with Kotlin files under Java packages, but it’s a good practice to keep them separated.

We’ll be creating a very simple function that just prints Hello World! when executed. Since it’ll be a simple function, I am just adding it as a top-level main() function.