PHP Static Methods

PHP - Static Methods

The static keyword is how you create static methods and properties.

What makes a static method special is that you can call it directly, with no need to make an instance of its class.

Declare a Static Method

Adding a static method to a class takes one extra keyword, static:

Static method declaration syntax

The static keyword goes ahead of the function name in the declaration:

<?php
class ClassName {
  public static function staticMethod() {
    echo "Hello World!";
  }
}
?>

Access a Static Method

Calling a static method takes three parts: first the class name, then a double colon (::), and finally the method name.

The next example declares a static method called welcome() and calls it in exactly that form. Notice that no object is ever created:

Example

Call a static method through its class name:

Create a PHP class called greeting with a static method welcome() that echoes "Hello World!". Call the static method directly using the class name without creating an instance.

> Output: PHP script

Prompt

Create a PHP class called greeting with a static method welcome() that echoes "Hello World!". Call the static method directly using the class name without creating an instance.

Output: PHP script

<?php
class greeting {
  // static method
  public static function welcome() {
    echo "Hello World!";
  }
}

// Call static method directly
greeting::welcome();
?>

Example

Here, a static method sum() is declared and then called in the same form: class name, ::, method name:

Create a PHP class called calc with a static method sum() that takes two parameters and returns their product. Call it with 6 and 4, then echo the result.

> Output: PHP script

Prompt

Create a PHP class called calc with a static method sum() that takes two parameters and returns their product. Call it with 6 and 4, then echo the result.

Output: PHP script

<?php
class calc {
  // static method
  public static function sum($x, $y) {
    return $x * $y;
  }
}

// Call static method
$res = calc::sum(6, 4);
echo $res;
?>

Static method access syntax

The general form of a static method call:

<?php
ClassName::staticMethod();
?>

PHP - More on Static Methods

Static and non-static methods can live side by side in a class. To reach a static method from another method of the same class, write self and a double colon (::) before its name:

Example

Here, the constructor calls a static method of its own class through self:

Create a PHP class called greeting with a static method welcome() that echoes "Hello World!" and a constructor that calls the static method using the self keyword.

> Output: PHP script

Prompt

Create a PHP class called greeting with a static method welcome() that echoes "Hello World!" and a constructor that calls the static method using the self keyword.

Output: PHP script

<?php
class greeting {
  // static method
  public static function welcome() {
    echo "Hello World!";
  }

  // non-static method
  public function __construct() {
    self::welcome();
  }
}

new greeting();
?>

Example

A method in another class can call a static method as well, as long as the static method is public:

Create two PHP classes: class A with a public static method welcome() that echoes "Hello World!", and class B with a method message() that calls A's static method. Create an instance of B and call message().

> Output: PHP script

Prompt

Create two PHP classes: class A with a public static method welcome() that echoes "Hello World!", and class B with a method message() that calls A's static method. Create an instance of B and call message().

Output: PHP script

<?php
class A {
  public static function welcome() {
    echo "Hello World!";
  }
}

class B {
  public function message() {
    A::welcome();
  }
}

$obj = new B();
echo $obj -> message();
?>

Example

Inside a child class, call the parent's static method with the parent keyword. In this case, the static method may be either public or protected.

Create a PHP class domain with a protected static method getWebsiteName() that returns "PromptCookbook". Then create a child class domainW3 that calls the parent static method in its constructor and stores the result. Echo the website name.

> Output: PHP script

Prompt

Create a PHP class domain with a protected static method getWebsiteName() that returns "PromptCookbook". Then create a child class domainW3 that calls the parent static method in its constructor and stores the result. Echo the website name.

Output: PHP script

<?php
class domain {
  protected static function getWebsiteName() {
    return "PromptCookbook";
  }
}

class domainW3 extends domain {
  public $websiteName;
  public function __construct() {
    $this->websiteName = parent::getWebsiteName();
  }
}

$domainW3 = new domainW3;
echo $domainW3 -> websiteName;
?>