There are times, however, when we want to extend the abilities of class but we don't want to define a completely new class. You will encounter these situations more and more as you plunge into Objective-C programming. Perhaps more importantly, you will find examples of category use throughout the Mac and iOS programming examples written by Apple and other developers.
So, to extend a class without sub-classing you have the option of using categories. Let's talk about how to do this.