Why you need to know objects and classes, and how to use them

This article describes the fundamentals of objects and classes in PHP V5, from the very basics through to inheritance, for experienced object-oriented programmers and those who have not yet been introduced to objects.

As a PHP programmer, you know variables and functions inside-out. Classes and objects, though, might be a different matter. It's possible to create perfectly good systems without defining a single class. Even if you decide to stay away from object-oriented programming in your own code, you will likely need to know object-oriented programming. For example, if you use a third-party library, such as those made available by PHP Extension and Application Repository (PEAR), you will find yourself instantiating objects and calling methods.

What are classes and objects?

Put simply, a class is a discrete block or bundle of variables and methods. These components usually coalesce around a single responsibility or set of responsibilities. In this article, you will create a class that collects methods for querying and populating a dictionary of terms and values.

A class can be used directly as a neat way of organizing data and functionality, very much like a bunch of functions and variables. This is to ignore a powerful dimension, however. Classes can be used to generate multiple instances in memory. Such instances are called objects. Each object has access to the same set of functions (called methods in an object-oriented context), and variables (called properties or instance variables), but the actual value of each variable may differ from object to object.

Think about a unit in a role-playing game -- a tank, perhaps. A class may lay down a set of variables for tanks: defensive and offensive capability, range, health, and so on. The class may also define a set of functions, including move() and attack(). While the system contains one tank class, this class may be used to generate tens or hundreds of tank objects, each potentially with its own characteristics of health or range. A class, then, is a blueprint or template for use in generating objects.

Perhaps the easiest way to understand classes and objects is to create some.