It's so good. It's so good that you explain it in an easy-to-understand way. I've already read 3 Java basic books and have come this far from the beginning of the roadmap curriculum. In order to perfectly master what I studied before, I looked at the theory again even though I knew it. Even though it's difficult to explain or understand polymorphism and abstract content, you explain it well. I hope that I can become an instructor who teaches this well in the future. (The only downside is that the course period is 12 months)