ch12-23,24 애너테이션 https://www.youtube.com/watch?v=i4V8ZI9Undc&list=PLW2UjW795-f6xWA2_MUhEVgPauhGl3xIp&index=144 객체지향개념만 (반복해서 듣고 익숙해질 것.) https://www.youtube.com/watch?v=CXuA31XcBZ0&list=PLW2UjW795-f5JPTsYHGAawAck9cQRw5TD
