I have taken many Java lectures, but I think that Professor Kim Young-han's basic lecture is the best. From Section 7, I knew the concepts in my head but couldn't express them in words, so I understood them vaguely. This lecture helped me understand them clearly. In particular, I think this is the first lecture where polymorphism and OCP were so clearly understood. The biggest advantage of Professor Kim Young-han's lectures, from Spring to Java, is the pictures that make it easy to understand and the code that helps you learn. I think the learning rate is higher than other lectures because the parts that I don't understand in words are understood through pictures and learned through code. Haha. Thanks to this lecture, I have a solid understanding of upscaling and downscaling, and the Java heap and stack area! I'm really looking forward to the next intermediate-advanced lecture that you are preparing. Until the next lecture comes out, I will wait to study Java by reviewing the lectures and studying recommended books. Thank you for the great lecture!!