Programming in Objective-C, Sixth Edition

Instances and Methods

A unique occurrence of a class is an instance, and the actions that are performed on the instance are called methods. In some cases, a method can be applied to an instance of the class or to the class itself. For example, washing your car applies to an instance. (In fact, all the methods listed in Table 3.1 can be considered instance methods.) Finding out how many types of cars a manufacturer makes would apply to the class, so it would be a class method.

Suppose you have two cars that came off the assembly line and are seemingly identical: They both have the same interior, same paint color, and so on. They might start out the same, but as each car is used by its respective owner, its unique characteristics or properties ...