When I was studying Kotlin, I don't think this lecture existed. If I had this lecture when I was studying Kotlin, I think I could have saved at least a month or more. Even though I studied by looking at all kinds of Kotlin books and documents, I wasted a lot of time on the gap between Java and Kotlin, and I still don't know how to use Kotlin in practice. (My current company doesn't use Kotlin, so I haven't used Kotlin in practice yet...) Anyway, for those who are interested in Kotlin and are studying it after using Java like me, I think this is the best lecture available. I've been using Java for less than two years and studying Kotlin for about two months, and I took this lecture and was able to organize a lot of things. Thank you.