Happy Coders

Class constants are fixed values defined using the const keyword inside a class. They are accessed using ClassName::CONSTANT and do not require an object. Constants cannot be changed once defined. Inside the class, use self::CONSTANT or parent::CONSTANT if inherited. They are ideal for configuration values or fixed settings.

1. Basic Example of Class Constant

class AppConfig {
    const SITE_NAME = "MyWebsite";
}

echo AppConfig::SITE_NAME; // Output: MyWebsite

File: class_constant.php

2. Using Class Constants Inside Methods

class Math {
    const PI = 3.14159;

    public function showPi() {
        return self::PI; // use self:: inside class
    }
}

$obj = new Math();
echo $obj->showPi(); // Output: 3.14159

File: constant_inside_class.php

3. Accessing Parent Class Constant in Child

class ParentClass {
    const MESSAGE = "Hello from parent";
}

class ChildClass extends ParentClass {
    public function showMsg() {
        return parent::MESSAGE;
    }
}

$child = new ChildClass();
echo $child->showMsg(); // Output: Hello from parent

File: constant_inheritance.php

4. Constants vs Variables