PHP Static Methods

What does static mean?

Normally a property or method belongs to a specific object, and you reach it through a variable holding that object. A static member is different: it belongs to the class as a whole. There is only one copy of a static property shared across every use of the class, and you can call a static method without ever creating an object. You declare these members with the static keyword.

<?php
class Counter
{
    public static int $count = 0;

    public static function increment(): void
    {
        self::$count++;
    }
}

Counter::increment();
Counter::increment();
echo Counter::$count; // 2
?>

Notice the double-colon operator (::), also called the scope resolution operator. You use it to reach static members from outside the class, as in Counter::increment(). Inside the class you refer to the class's own static members with the self keyword, as in self::$count.

self versus $this

Because static members are not tied to an object, you cannot use $this inside a static method; there is no particular object for it to point to. Instead you use self:: to reach other static members of the same class. Trying to access a non-static property from a static method will cause an error.

A common use: factory methods

A frequent use of static methods is a factory, a method that builds and returns an object in a convenient way. This lets you offer clear, named ways of constructing objects while keeping the constructor itself simple.

<?php
class Money
{
    private function __construct(public int $cents)
    {
    }

    public static function fromDollars(float $dollars): self
    {
        return new self((int) round($dollars * 100));
    }

    public function format(): string
    {
        return "$" . number_format($this->cents / 100, 2);
    }
}

$price = Money::fromDollars(19.5);
echo $price->format(); // $19.50
?>

• Declare static members with the static keyword.
• Access them through the class name and the :: operator from outside.
• Use self:: to reach static members from within the same class.
• You cannot use $this inside a static method.
• Static properties keep a single shared value across the whole program run.