Java to Kotlin Hack 1.0 + Redeem Codes

The app has two part
Learning by analogy. The first part has a cookbook style
Java and Kotlin snippets are shown next to each other. So your can recognise and remember the differences between the two languages.
The second part are quizzes. Here you can to test your Kotlin knowledge. The answers are given instantaneously. So you can also use it as a learning tool by trail and error.