Static Methods & Properties

Part of the Object Oriented Programming section of Coddy's PHP journey — lesson 17 of 91.

Just as properties can be static, methods can also belong to the class itself rather than to individual objects. Static methods are called on the class directly, without needing to create an instance first.

You declare a static method using the static keyword and call it with the class name and :: operator:

<?php
class MathHelper {
    public static function add($a, $b) {
        return $a + $b;
    }
    
    public static function multiply($a, $b) {
        return $a * $b;
    }
}

echo MathHelper::add(5, 3) . "\n";
echo MathHelper::multiply(4, 2);

Output:

8
8

Static methods work well with static properties. A common pattern is using a static method to manage shared class data:

<?php
class Counter {
    private static $count = 0;
    
    public static function increment() {
        self::$count++;
    }
    
    public static function getCount() {
        return self::$count;
    }
}

Counter::increment();
Counter::increment();
echo Counter::getCount();

Output:

Notice that static methods cannot use $this because there's no object instance. They can only access static properties and other static methods using self::.

Key Point: Static methods are useful for utility functions that don't need object state, or for managing class-level data. They provide functionality without requiring object instantiation.

Challenge

Easy

Let's build an ID generator system that uses static methods and properties to create unique identifiers without needing to instantiate objects.

You'll create two files to organize your code:

IdGenerator.php — Define an IdGenerator class that manages unique ID generation using only static members. The class should have a private static property $lastId starting at 0 and a private static property $prefix set to "ID". Create a static method generate() that increments the last ID and returns a formatted string combining the prefix and the new ID (like "ID1", "ID2", etc.). Add a static method setPrefix($newPrefix) that changes the prefix, and a static method getLastId() that returns the current value of $lastId.
main.php — Include the IdGenerator class file. Generate two IDs using the default prefix and print each one on its own line. Then change the prefix to "USER" using the static method, generate two more IDs, and print each one. Finally, print the last ID number by calling the appropriate static method.

Remember that static methods are called directly on the class using ClassName::methodName(), and inside the class you access static properties with self::$propertyName. Since there's no object instance, you cannot use $this in static methods.

Your output should show the progression of IDs with different prefixes, demonstrating how static properties maintain their values across multiple method calls.

Cheat sheet

Static methods belong to the class itself and are called without creating an instance. Declare them using the static keyword and call them with the class name and :: operator:

<?php
class MathHelper {
    public static function add($a, $b) {
        return $a + $b;
    }
}

echo MathHelper::add(5, 3); // 8

Static methods can access static properties using self:::

<?php
class Counter {
    private static $count = 0;
    
    public static function increment() {
        self::$count++;
    }
    
    public static function getCount() {
        return self::$count;
    }
}

Counter::increment();
echo Counter::getCount(); // 1

Static methods cannot use $this because there's no object instance. They can only access static properties and other static methods using self::.

Static methods are useful for utility functions that don't need object state, or for managing class-level data without requiring object instantiation.

Try it yourself

<?php

// Include the IdGenerator class file
require_once 'IdGenerator.php';

// TODO: Generate two IDs using default prefix and print each on its own line

// TODO: Change the prefix to "USER" using the static method

// TODO: Generate two more IDs and print each on its own line

// TODO: Print the last ID number using the appropriate static method

?>

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Static Methods & Properties

Cheat sheet

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