Objective-C Fundamentals

56 CHAPTER 3 An introduction to objects
3.1 A whirlwind tour of object-oriented programming concepts
In this chapter we can’t do justice to every concept associated with object-oriented
programming (also termed OOP, for short). Instead, the goal of this chapter is to
make sure you have a solid understanding of the fundamental concepts and benefits
of object-oriented programming and a working knowledge of the terminology.
Throughout this book, we discuss object-oriented programming concepts as they
apply to Objective-C and expand on what’s covered in this chapter. Let’s get started by
learning what’s so wrong with C.
3.1.1 What’s wrong with procedural-based languages such as C?
In very broad brush strokes, a procedural language requires greater concentration
and observance of manually enforced or informal rules than does an object-oriented
language.
One reason for this is that procedural languages focus on dividing the application’s
source code into individual functions, but generally their ability to control
access to data is less fine-grained. Data will generally belong to a particular function or
be globally accessible by any function. This causes problems when several functions
need to access the same data. To be available to more than one function, such variables
must be global, but global data can be accessed (or worse yet, modified in inappropriate
ways) by any function in the application.
Object-oriented programming, on the other hand, attempts to merge these two concepts.
When developing a new application, you first think of the different kinds of
things represented in it, then the type of data it’s required to store, and then the actions
each thing should be able to perform. These “things” are commonly called objects.
3.1.2 What are objects?
When developing an object-oriented application, you’re creating a miniature model
of a system. That model is constructed from one or more building blocks called objects.
As an example, in a drawing application, a user may create three objects representing
a circle and two rectangles. Each object has associated data that is relevant to itself.
The circle object’s data may describe a radius, while the rectangle objects, to be recognized
as rectangles, will probably require a width and height to be stored as their data.
Objects in an application can usually be grouped into similar types. For example,
all circles will require that similar attributes be specified to describe their size, shape,
and color. But the attributes required to describe circles will most likely be different
from the attributes required for all of the objects of type rectangle.
Individual objects in an application are created from a cookie-cutter-type template
called a class. A class describes what type of data an object must store and the type of
actions or operations it can perform.