Behavioral Design Patterns

In the last two chapters, we have learned patterns that aid us in the creation of objects and with building complex object structures. Now it's time to move onto another aspect of software design, which concerns the behavior of components. In this chapter, we will learn how to combine objects and how to define the way they communicate so that the behavior of the resulting structure becomes extensible, modular, reusable, and adaptable. Problems such as "How do I change parts of an algorithm at runtime?", "How can I change the behavior of an object based on its state?", and "How can I iterate over a collection without knowing its implementation?" are the typical kinds of problems solved by the patterns presented in this chapter.

You've already met a notable member of this category of patterns, and that is the Observer pattern, which we presented in Chapter 3, Callbacks and Events. The Observer pattern is one of the...