Chapter 4. Object Interactions

As you learned in Chapter 3, objects are the building blocks of an object-oriented (OO) software system. In such a system, objects collaborate with one another to accomplish common system goals, similar to ants in an anthill, employees of a corporation, or cells in your body. Each object has a specific structure and "mission"; these respective missions complement one another in accomplishing the mission of the system as a whole.

In this chapter, you'll learn:

• How external events set the objects within an OO application in motion.

• How methods can be used to specify an object's behaviors. We'll talk about the various code elements that make up a method and how methods are invoked.

• How objects publicize their methods as services to one another.

• How objects communicate with one another to request one another's services.

• How objects maintain their data and how they "guard" their data to ensure its integrity.

• About the power of encapsulation and how it can be used to limit "ripple effects" when the private implementation details of a class change.

• How constructors can be used to initialize field values when an object is instantiated.