Constants in Interface in OOP in PHP

Interfaces cannot contain class properties, but they can contain constants. Interface constants work exactly the same as class constants, with the exception that they cannot be overridden by an inheriting class or interface.

For example, let's create an interface iSphere, which will describe a class for working with a sphere. For this sphere, we will need to find the volume and surface area. For this, we will need the number Pi. Let's define it as a constant of our interface:

<?php
	interface iSphere
	{
		const PI = 3.14; // the number PI as a constant
		
		// Sphere constructor:
		public function __construct($radius);
		
		// Method for finding the volume of a sphere:
		public function getVolume();
		
		// Method for finding the surface area of a sphere:
		public function getSquare();
	}
?>

Create a class Sphere that will implement the interface iSphere.