Constants in classes in PHP

Introduction

Constants in classes hold values that do not change. They help keep important data safe and easy to use.

When you want to store a fixed value related to a class, like a version number.

When you need a value that should be the same for all objects of a class.

When you want to avoid magic numbers or strings scattered in your code.

When you want to give a name to a value that never changes, making code clearer.

Syntax

PHP

class ClassName {
    const CONSTANT_NAME = value;
}

Constants are declared with the keyword const inside a class.

Constant names are usually uppercase by convention.

Examples

This class has a constant WHEELS set to 4.

PHP

class Car {
    const WHEELS = 4;
}

Here, PI is a constant representing the value of pi.

PHP

class Circle {
    const PI = 3.14159;
}

This class defines two string constants for user roles.

PHP

class User {
    const ROLE_ADMIN = 'admin';
    const ROLE_GUEST = 'guest';
}

Sample Program

This program defines a class Fruit with a constant COLOR. It then prints the color using the constant.

PHP

<?php
class Fruit {
    const COLOR = 'red';
}

echo "The color of the fruit is " . Fruit::COLOR . ".";

Important Notes

You access class constants using the scope resolution operator ::, like ClassName::CONSTANT_NAME.

Constants cannot be changed once set. They are different from variables.

Constants are always public and can be accessed without creating an object.

Summary

Constants store fixed values inside classes.

Use const keyword to declare them.

Access constants with ClassName::CONSTANT_NAME.