Kotlin is one more jvm programming language. JetBrains have been developing it since 2010. When I got known about it on some conference I worked with java 6. The project was too big and had a lot of dependencies, so it was very hard to migrate to java 7 and we even didn’t think about java 8. The main advantage of kotlin that attracted me is possibility to use additional features that can be complied to jvm 6. One more nice feature is that kotlin and java code are compatible with each other. It allows migrating step by step, class by class. For training I decided to rewrite my small project on kotlin. My feedback is below.