Page 211 - Beginning PHP 5.3

Chapter 8: Objects
Within the Car class, a static property, $numberSold , is declared and also initialized to 123 . Then,
outside the class definition, the static property is incremented and its new value, 124 , is displayed.

Static properties are useful when you want to record a persistent value that ’ s relevant to a particular
class, but that isn ’ t related to specific objects. You can think of them as global variables for classes. The
nice thing about static properties is that code outside the class doesn ’ t have to create an instance of
the class — that is, an object — in order to access the property.

Class Constants
You learned in Chapter 3 that you can create constants — special identifiers that hold fixed values
throughout the running of your script. PHP also lets you create constants within classes. To define a class
constant, use the keyword const , as follows:

class MyClass {
const MYCONST = 123;

}

As with normal constants, it ’ s good practice to use all - uppercase letters for class constant names.
Like static properties, you access class constants via the class name and the :: operator:

echo MyClass::MYCONST;
Class constants are useful whenever you need to define a fixed value, or set a configuration option, that ’ s
specific to the class in question. For example, for the Car class you could define class constants to
represent various types of cars, then use these constants when creating Car objects:

class Car {
const HATCHBACK = 1;
const STATION_WAGON = 2;
const SUV = 3;

public $model;
public $color;
public $manufacturer;
public $type;
}

$myCar = new Car;

$myCar-> model = “Dodge Caliber”;
$myCar-> color = “blue”;

$myCar-> manufacturer = “Chrysler”;
$myCar-> type = Car::HATCHBACK;

echo “This $myCar-> model is a “;
switch ( $myCar-> type ) {

case Car::HATCHBACK:
echo “hatchback”;
break;
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