This module explores the variety of behavioral design patterns, patterns that describe the ways objects and classes interact and divide responsibilities among themselves. A behavioral pattern abstracts an action you want to take from the object or class that takes the action. By changing the object or class, you can change the algorithm used, the objects affected, or the behavior, while still retaining the same basic interface for client classes.
A good toolbox of behavioral patterns allows you to solve many thorny problems you're likely to encounter when designing object-oriented systems. These include enumerating lists, responding to changes of state in an object, serializing and deserializing objects without penetrating data encapsulation, and more.

In this module, you will learn:

1. How programmers use behavioral design patterns
2. About the most commonly used design patterns
3. When to use the Observer and Mediator patterns
4. How to use the Mediator pattern to manage the different traffic lights