Now that you have spent three days exploring how object-oriented programming is implemented in Java, you're in a better position to decide how useful it can be in your own programming.
If you are a "glass is half empty" person, object-oriented programming is a level of abstraction that gets in the way of what you're trying to use a programming language for. You will learn more about why OOP is thoroughly ingrained in Java in the coming days.
If you are a "glass is half full" person, object-oriented programming is worth using because of the benefits it offers: improved reliability, reusability, and maintenance.
Today you learned how to deal with objects: creating them, reading their values and changing them, and calling their methods. You also learned how to cast objects from one class to another or from a data type to a class.
At this point you possess the skills to handle most simple tasks in the Java language. All that remains are arrays, conditionals, and loops (which are covered tomorrow), and how to define and use classes on Day 5.