This is the best review material for job seekers who are already working or have studied a lot, and for those who have already started, this lecture provides more plus alpha than simply reading a basic book. The advantages, such as the reason why String addition operations should not be used in loops and the reason why Enum should be used, help build more solid skills by explaining contents that are not well mentioned in basic books, and explain polymorphism better than Java basic books on the market. As a long-time student, I can feel that the lectures that have been given since declaring themselves as full-time educators provide better lecture materials and have easier-to-understand explanations and communication skills.