16.17. Singleton Classes
In the world of OO design patterns, there is one that is especially common, called the Singleton pattern. It is explained later, but an implication of the pattern is that there is only one instance of a class instantiatednever two. In other words, it is a "singleton" instance. In a UML diagram, such a class can be marked with a '1' in the upper right corner of the name compartment. See Figure 16.17.
Figure 16.17. Showing a singleton.
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