Run single kotlin class with main function in android studio

Question

I am trying to get familiar with Kotlin to use in my android apps. So first I want to try out some simple kotlin examples, just to get familiar with syntax of kotlin.

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Answer 1

Tested on Android Studio 3.1.3

Note that this is an edited version of my other answer.

Using this method you can have Java/Kotlin modules and Android modules in the same project and also have the ability to compile and run Java/Kotlin modules as stand alone projects.

1. Open your Android project in Android Studio. If you do not have one, create one.
2. Click File > New Module. Select Java Library and click Next.
3. Fill in the package name, etc and click Finish. You should now see a Java module inside your Android project.
4. Add your Java/Kotlin code to the Java module you've just created.
5. Click on the drop down to the left of the run button. Click Edit Configurations...
6. In the new window, click on the plus sign at the top left of the window and select Application
7. A new application configuration should appear, enter in the details such as your main class and classpath of your module.
8. Click OK.

9. Next we need to add the Kotlin plugin. Add the following code to your project level build.gradle (lines to add are denoted by >>>):

   buildscript {
       >>> ext.kotlin_version = '1.2.51'
       repositories {
           google()
           jcenter()
       }
       dependencies {
           classpath 'com.android.tools.build:gradle:3.1.3'
           >>> classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
   
           // NOTE: Do not place your application dependencies here; they belong
           // in the individual module build.gradle files
       }
   }
   ...
   

10. Add the following code to your module level build.gradle (lines to add are denoted by >>>):

    apply plugin: 'java-library'
    >>> apply plugin: 'kotlin'
    
    dependencies {
        implementation fileTree(dir: 'libs', include: ['*.jar'])
        >>> implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
        >>> runtimeClasspath files(compileKotlin.destinationDir)
    }
    ...
    

Now if you click run, this should compile and run your Java/Kotlin module.

If you get the error Error: Could not find or load main class..., just enter your main class (as you've done in step 7) again even if the field is already filled in. Click Apply and then click Ok.