Class constants can be useful if you need to define some constant data within a class.
A class constant is declared inside a class with the const keyword.
A constant cannot be changed once it is declared.
Class constants are case-sensitive. However, it is recommended to name the constants in all uppercase letters.
We can access a constant from outside the class by using the class name followed by the scope resolution operator (::) followed by the constant name, like here:
<?php
class Goodbye {
const LEAVING_MESSAGE = "Thank you for visiting W3Schools.com!";
}
echo Goodbye::LEAVING_MESSAGE;
?>
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:
<?php
class Goodbye {
const LEAVING_MESSAGE = "Thank you for visiting W3Schools.com!";
public function byebye() {
echo self::LEAVING_MESSAGE;
}
}
$goodbye = new Goodbye();
$goodbye->byebye();
?>