Behavioral Patterns

1. Behavioral patterns are those patterns that are most specifically
   concerned with communication between objects. In this chapter, we’ll see
   that:
   
   •The Observer pattern defines the way a number of classes can be notified
   of a change,
   •The Mediator defines how communication between classes can be
   simplified by using another class to keep all classes from having to know
   about each other.
   •The Chain of Responsibility allows an even further decoupling between
   classes, by passing a request between classes until it is recognized.
   •The Template pattern provides an abstract definition of an algorithm, and
   •The Interpreter provides a definition of how to include language elements
   in a program.
   •The Strategy pattern encapsulates an algorithm inside a class,
   •The Visitor pattern adds function to a class,
   •The State pattern provides a memory for a class’s instance variables.
   •The Command pattern provides a simple way to separate execution of a
   command from the interface environment that produced it, and
   •The Iterator pattern formalizes the way we move through a list of data
   within a class.