Through this lecture, I learned the concept of polymorphism. I think I can practice a lot with this concept according to the situation! When writing code, I always had a lack of flexibility because of the parts that act according to the if statement condition, but now I know how to separate them. And the Null Object Pattern was a good tip! After learning polymorphism, I became interested in design patterns and I think I understand Spring a little better, so it was a satisfying lecture! Thank you.