Static Properties

The “static” keyword in PHP is used to define static properties and static methods in a PHP class. It may be noted that the static keyword is also used to define static variable, and static anonymous functions. Read this chapter to learn about the static properties in a PHP class.

In a class definition, a variable declared with a static qualifier becomes its static property. The static keyword may appear before or after the access modifier.

Declare a Static Property

Here is how you can declare a static property in PHP −

staticprivate$var1;publicstatic$var2;

Using Type Hints with Static Properties

If you want to use type hints, the type must not be before the static keyword.

staticprivatestring$var1;publicstaticfloat$var2;

The value of the static property in a class is not accessible by its object (with the -> operator). Doing so will result in a notice stating Accessing static property myclass::$var1 as non static. Instead, the static properties are accessed using the Scope Resolution Operator represented by the “::” symbol.

Example

Take a look at the following example −

<?php
   class myclass {
  static string $var1 = "My Class";
  function __construct() {
     echo "New object declared" . PHP_EOL;
  }
   }
   $obj = new myclass;
   echo "accessing static property with scope resolution operator: " . myclass::$var1 . PHP_EOL;
   echo "accessing static property with -> operator: ". $obj->var1 . PHP_EOL;
?>

Output

It will produce the following outcome −

New object declared
accessing static property with scope resolution operator: My Class
PHP Notice:  Accessing static property myclass::$var1 as non static in hello.php on line 14

Using the self Keyword

To access the static property from inside a method, refer to the current class with the self keyword. In the following example, the class has an integer static property, which is incremented every time a new object is declared.

<?php
   class myclass {
   
  /* Member variables */
  static int $var1 = 0;
  function __construct(){
     self::$var1++;
     echo "object number ". self::$var1 . PHP_EOL;
  }
   }
   for ($i=1; $i<=3; $i++) {
  $obj = new myclass;
   }
?>

Output

It will produce the below output −

object number 1
object number 2
object number 3

Using the parent Keyword

The static property of a base class can be used inside a function of the inherited class by referring to the base by parent keyword. You need to use the “parent::static_property” syntax.

Take look at the following example −

<?php
   class myclass {
   
  /* Member variables */
  static int $var1 = 0;
  function __construct() {
     self::$var1++;
     echo "object number ". self::$var1 . PHP_EOL;
  }
   }

   class newclass extends myclass{
  function getstatic() {
     echo "Static property in parent class: " . parent::$var1 . PHP_EOL;
  }
   }
   $obj = new newclass;
   $obj->getstatic();
?>

Output

It will generate the following output −

object number 1
Static property in parent class: 1

Constant vs Static Property

Here is a simple table showing the difference between constants and static properties in PHP −

Aspect	Constant (‘const’)	Static Property (‘static’)
Keyword	‘const’	‘static’
Value Mutability	Immutable — value cannot be changed after declaration.	Mutable — value can be changed during script execution.
Access	Accessed with ‘ClassName::CONSTANT_NAME’.	Accessed with ‘ClassName::$propertyName’.
Value Initialization	Must be initialized with a constant value (not a function).	Can be initialized with a constant value or literal.
Data Types	Supports scalar values, arrays (PHP 5.6+), and class objects (PHP 7.1+).	Supports all data types, including complex objects.
Inheritance	Inherited by child classes but cannot be overridden.	Inherited and can be overridden in child classes.
Context Usage	Available both inside and outside the class.	Mainly used for class-level state or counters.
Access with ‘$this’	Not accessible via object instance.	Not accessible via object instance (‘$this’).
Example Declaration	‘const PI = 3.14;’	‘public static float $pi = 3.14;’
Example Access	‘echo MyClass::PI;’	‘echo MyClass::$pi;’