Class Constants in PHP

In this tutorial, you shall learn how to define constant properties in a class in PHP, with the help of example programs.

PHP – Class Constants

We can declare constant properties in a class using const keyword.

A property that is declared constant must be initialised in the class definition itself. This constant can never be re-initialised.

In this tutorial, we define a constant in the class and print it to output.

Syntax

The syntax to declare a constant $LEGAL_AGE, in Person class is

class Person() {
    const $LEGAL_AGE = 18;
}

Please note that we initialised the constant during the declaration.

To access the constant via a class object, use the following syntax.

$classObject::CONSTANT_NAME

For the example of Person class, the expression would be

$person1::LEGAL_AGE

where $person1 is an object of type Person.

Examples

1. A simple example for class constant

In this example we take a class Person and declare a constant $LEGAL_AGE. We initialise this constant in the declaration itself.

PHP Program

<?php
  class Person {
    const LEGAL_AGE = 18;
    //other properties and methods
  }
  
  //create object
  $person1 = new Person();

  //access constant property
  echo $person1::LEGAL_AGE;
?>

Output

2. Access class constant via class method

In this example we take a class Person and declare a constant $LEGAL_AGE. We access this constant from the class method $printLegalAge().

PHP Program

<?php
  class Person {
    const LEGAL_AGE = 18;
    
    public function printLegalAge() {
      echo "Legal Age : " . self::LEGAL_AGE;
    }
  }
  
  //create object
  $person1 = new Person();

  //access constant property
  echo $person1->printLegalAge();
?>

Output

Conclusion

In this PHP Tutorial, we learned how to declare a constant in a class, and how to access it from within the scope, with examples.