Implementing the Observer pattern

To implement the Observer pattern, we will first need to define our Subject and Observer classes. We will then need to derive concrete classes from these classes to incorporate our application specifics and to put our pattern in motion. Let’s get started!

Creating an Observer, Subject, and domain-specific derived classes

In our example, we will create Subject and Observer classes to establish the framework for registering an Observer with a Subject and for the Subject to Notify() its set of observers of a state change it may have. We will then derive from these base classes descendent classes we are accustomed to seeing – Course and Student, where Course will be our concrete Subject and Student will become our concrete Observer.

The application we will model will involve a course registration system and the concept of a waitlist. As we have seen before in Question 2 of Chapter 10, Implementing Association, Aggregation, and Composition...