Even though I was using Spring, I didn't have a clear and clear understanding of core concepts such as IoC, DI, and AOP. I always read blog posts, but my head was not organized because the theories I collected from various places were mixed together. However, after listening to this lecture, I felt like the concepts were organized. In fact, I think this lecture has some parts that are difficult for complete beginners. However, I felt that it was a satisfactory lecture because I felt that it was trying to convey difficult concepts a little more easily. After listening to this lecture, I want to take the paid lecture too! Thank you : )