In this chapter, we covered more theory than in any other chapter. If you haven't memorized everything, then you have succeeded completely. If you just understand that OOP is about writing reusable, extendable, and efficient code through encapsulation, inheritance, and polymorphism, then you have the potential to be a Java master. Simply put, OOP enables us to use other people's hard work even when those people were not aware of exactly what we would be doing at the time they did the work. All you have to do is keep practicing, so let's make a retro game in the next chapter.