Learning Java, 6th Edition

Chapter 5. Objects in Java

In this chapter, we get to the heart of Java and explore its object-oriented aspects. The term object-oriented design refers to the art of decomposing an application into some number of objects, which are self-contained application components that work together. The goal is to break your problem down into smaller problems that are simpler and easier to handle and maintain. Object-based designs have proven themselves over the years, and object-oriented languages such as Java provide a strong foundation for writing applications—from the very small to the very large. Java was designed from the ground up to be an object-oriented language, and all of the Java APIs and libraries are built around solid object-based design patterns.

An object design methodology is a system or a set of rules created to help you break down your application into objects. Often this means mapping real-world entities and concepts (sometimes called the problem domain) into application components. Various methodologies attempt to help you factor your application into a good set of reusable objects. This is good in principle, but the problem is that good object-oriented design is still more art than science. While you can learn from off-the-shelf design methodologies, none of them will help you in all situations. The truth is that there is no substitute for experience.

We won’t try to push you into a particular methodology here; there are shelves full of books to do that.¹ Instead, ...