For a developer, building iOS and OS X applications requires a lot of time in creating and handling objects. In Objective-C, like any other object-oriented programming language, the object acts like a data package with predefined behaviors. We can think about an application as an environment containing objects that connect with each other, passing and receiving information such as how to build a graphical interface, how to proceed with user interactions, how and where to store and take data from, how to perform calculations, and much more. The complexity of tasks that can be performed by an object can be very large, but it's not reflected on the complexity to create an object.

Cocoa (for OS X) and Cocoa Touch (iOS) already provide a library containing an extensive list of objects for you to use as they are or create your own objects based on them—we call it code reuse.

One of the most important development processes is thinking about the...