Source organization

By default, new Kotlin files are saved in src/main/java/, which makes it easy to see both Kotlin and Java files in one location. If you'd prefer to separate your Kotlin files from your Java files, you can put Kotlin files under src/main/kotlin/ instead. If you do this, then you also need to include this directory in your sourceSets configuration, as shown below:

android {
    sourceSets {
        getByName("main") {
            java.srcDir("src/main/kotlin")
        }
    }
}

NOTE

add it in gradle app