Page 206 - Beginning PHP 5.3

Part II: Learning the Language
For example, the Car class might indicate merely that cars should have a color, whereas a specific myCar
object might be colored red.

The distinction between classes and objects is often confusing to those new to OOP. It helps to think of
classes as something you create as you design your application, whereas objects are created and used
when the application is actually run.

Properties

In OOP terminology, the characteristics of a class or object are known as its properties . Properties
are much like regular variables, in that they have a name and a value (which can be of any type).
Some properties allow their value to be changed and others do not. For example, the Car class might
have properties such as color and weight . Although the color of the car can be changed by giving it
a new paint job, the weight of the car (without cargo or passengers) is a fixed value.

Methods

The behaviors of a class — that is, the actions associated with the class — are known as its methods .
Methods are very similar to functions; in fact, you define methods in PHP using the function statement.

Like functions, some methods act on external data passed to them as arguments, but an object ’ s method
can also access the properties of the object. For example, an accelerate method of the Car class might
check the fuel property to make sure it has enough fuel to move the car. The method might then update
the object ’ s velocity property to reflect the fact that the car has accelerated.

The methods of a class, along with its properties, are collectively known as members of the class.

Creating Classes and Objects in PHP
Although the theory behind classes and objects can get quite involved, classes and objects are actually
really easy to create in PHP. As you ’ d imagine, you need to create a class before you create an object
belonging to that class. To create a class, you use PHP ’ s class keyword. Here ’ s a really simple class:
class Car {
// Nothing to see here; move along
}

This code simply defines a class called Car that does nothing whatsoever — it merely includes a
comment. (You add some functionality to the class shortly.) Notice that a class definition consists of the
class keyword, followed by the name of the class, followed by the code that makes up the class,
surrounded by curly brackets ( { } ).

A common coding standard is to begin a class name with a capital letter, though you don ’ t have to do
this. The main thing is to be consistent. You can find out more about coding standards in Chapter 20 .

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