The singleton pattern is another GoF design pattern that is used to restrict the instantiation of a class to one object. It is used in situations where actions within a system need to be coordinated or access to data needs to be limited. For example, if access to a file needs to be restricted within an application to a single writer, then a singleton could be used to prevent multiple objects from trying to write to the file at the same time. In our scenario, we are going to use a singleton to maintain the collection of books and their inventory.
The value of the singleton pattern is more apparent when it is illustrated using examples. This section will start with a basic class and then go on to identify the different issues that the singleton pattern addresses. These issues will be identified, and the class will be updated and then verified by unit tests...