On May 2019, Google announced Kotlin a preferred language for Android development. Every industry has a topic to “holy-war” about. Competition between Kotlin and Java used to be a stumbling point of Android development. Now it is Kotlin-first approach. Despite the fact that Kotlin and Java are not competitors anymore, developers and business projects still have reasons to use Java and need some time, knowledge, and effort to switch. What are the advantages of Kotlin or where Java still rules in developing a mobile app and digital business assets?