This is the basics of buildup. The content covered at the beginning will definitely become the cornerstone of what follows. Thanks to the instructor, 'polymorphism' was firmly engraved in my head! I really didn't understand what polymorphism was, but it was really great that you drew the memory structure and explained its purpose. In particular, there were many parts that I was confused about when dealing with Spring, but I found out that it was because I was shaken by Java. Thank you for making such a great lecture! I will pray every day for the intermediate and advanced Java edition to come out soon!!