Kotlin

Kotlin is the dominant Android development language and is rapidly replacing Java for new JVM server-side code. Google formally endorsed Kotlin as the preferred Android language in 2019, and by 2025, 95% of new Android apps in the Play Store use Kotlin. What is less known: Kotlin Multiplatform now allows sharing business logic between Android, iOS, and web — a genuine cross-platform story without the performance compromises of React Native or Flutter. For Android developers, Kotlin is non-negotiable. For backend JVM developers, Kotlin coroutines, null safety, and concise syntax make it a significant productivity improvement over Java.