PHP 5 Tutorials - Static Data Members and Methods

Posted on February 12th, 2008 by admin

In this tutorial you will learn all about static data members and methods

Meaning of static data members
Meaning of static methods
Defining static data members in PHP5
Defining static methods in PHP5
Accessing static data members in PHP5
Accessing static methods in PHP5
Rules to keep in mind for static methods

Meaning of static data members

A data member that is commonly available to all objects of a class is called a static member. Unlike regular data members, static members share the memory space between all objects of the same class.

Meaning of static methods

A static method is a class method that can be called without creating an instance of a class. Such methods are useful when creating utility classes.

Defining static data members in PHP5

To define a static member in PHP5 you need to prefix the class member name with the keyword ’static’. Look at the example below.

 
class Customer {
 
	private $first_name; // regular member
	static public $instance_count; //static data member
 
}

In the above example $instance_count is declared as a static data member

Defining static methods in PHP5

To define a static data methods in PHP5 you need to prefix the class method name with the keyword ’static’. Look at the example below.

 
class Customer {
 
	public function getFirstName() {
		//body of method
	}
 
	static public function getInstanceCount() {
		//body of method
	}
}

In the above example getInstanceCount is declared as a static method

Accessing static data members in PHP5

A static member data can be accessed using the name of the class along with the scope resolution operator (::) i.e. you don’t need to create an instance of that class

Look at the example below:

 
class Customer {
 
	static public $instance_count = 0; //static data member
 
	public function __construct() {
		Customer::$instance_count++;
	}
 
	public function __destruct() {
		Customer::$instance_count--;
	}
 
	public function getFirstName() {
		//body of method
	}
 
	static public function getInstanceCount() {
		//body of method
	}
}
 
$c1 = new Customer();
$c2 = new Customer();
 
echo Customer::$instance_count;

Output:
2

In the above example, $instance_count is a static data member. Every time a new object is created the constructor is executed and the $instance_count variable is incremented by one. To echo the value contained in $instance_count variable, we use the :: (scope resolution) operator.

Accessing static method in PHP5

A static method can be accessed using the name of the class along with the scope resolution operator (::) i.e. you don’t need to create an instance of that class. However, you can also access it with an instance variable.

Look at the example below:

 
class Customer {
 
	static public $instance_count = 0; //static data member
 
	public function __construct() {
		Customer::$instance_count++;
	}
 
	public function __destruct() {
		Customer::$instance_count--;
	}
 
	public function getFirstName() {
		//body of method
	}
 
	static public function getInstanceCount() {
		return Customer::$instance_count;
	}
}
 
$c1 = new Customer();
$c2 = new Customer();
 
echo Customer::getInstanceCount(); //this is using the scope resolution operator
echo $c1->getInstanceCount(); //this is using the instance variable