PHP Class Constants: Define and Use Constants in OOP with Examples

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PHP OOP - Class Constants

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PHP - Class Constants

Class constants in PHP are fixed values that cannot be changed once they are defined.

Class constants are case-sensitive. However, it is recommended to name the constants in all uppercase letters.

Key Features of Class Constants:

Declared using const inside a class.
Cannot be changed after declaration.
Do not use the $ symbol.
Accessed using ClassName::CONSTANT_NAME.
Can be inherited but cannot be overridden.

Syntax

class ClassName {
  const CONSTANT_NAME = value;
}

Defining and Accessing Class Constants

Example

<?php

class Car {

const WHEELS = 4; // Defining a constant

}

// Accessing the constant using the class name

echo "A car has " . Car::WHEELS . " wheels.<br>";

Try it yourself

Or, we can access a constant from inside the class by using the self keyword followed by the scope resolution operator (::) followed by the constant name, like here:

Example

<?php

class Car {

const WHEELS = 4; // Defining a constant

public function getWheels() {

return "This car has " . self::WHEELS . " wheels.";

}

// Accessing the constant using the class name

echo "A car has " . Car::WHEELS . " wheels.<br>";

// Accessing the constant using `self::` inside the class

$myCar = new Car();

echo $myCar->getWheels();

Try it yourself

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