The main purpose of Java / Kotlin is flexibly scalable and fault-tolerant server-side solutions on a microservice architecture. Development in Java is fast enough due to the huge number of frameworks and free source libraries that fulfill almost all needs. Kotlin is a fairly young language, but it has already gained popularity among programming languages. Moreover, it is recognized by Google as a first class language on Android. The concepts embedded in the language allow you to write more robust code while avoiding common mistakes.