PHP OOP - Class Constants

In PHP Object-Oriented Programming (OOP), class constants are similar to regular constants, but they are defined within a class and are accessed using the scope resolution operator (::). Class constants provide a way to define values that remain constant throughout the execution of the script and are associated with a specific class.

Example

class MyClass {
    // Define a class constant
    const MY_CONSTANT = "Hello, world!";
    
    // Method to access the class constant
    public function getConstant() {
        return self::MY_CONSTANT; // Accessing class constant using self keyword
    }
}

// Accessing the class constant from outside the class
echo MyClass::MY_CONSTANT . "\n";

// Creating an object of the class to access the constant through a method
$obj = new MyClass();
echo $obj->getConstant() . "\n";

You can click on above box to edit the code and run again.

Output

In this example:

MY_CONSTANT is a class constant defined within the MyClass class using the const keyword.
It's accessed using the scope resolution operator (::) outside the class.
Inside the class, it's accessed using the self keyword followed by the scope resolution operator (::).
Class constants are accessed without the use of the dollar sign ($).
They are useful for defining values that should not change throughout the execution of the script, such as configuration settings or fixed values.
Class constants are case-sensitive by default and can be accessed from both static and non-static contexts.