Constants in classes in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing class constant

What is the output of this PHP code?

PHP

<?php
class Fruit {
    const NAME = 'Apple';
}
echo Fruit::NAME;

A NAME

B Apple

C Error: Cannot access constant

D null

💡 Hint

Class constants are accessed with :: operator.

The constant NAME inside class Fruit is accessed using Fruit::NAME and outputs 'Apple'.

❓ Predict Output

intermediate

Output of constant in subclass

What will this code output?

PHP

<?php
class Vehicle {
    const WHEELS = 4;
}
class Bike extends Vehicle {
    const WHEELS = 2;
}
echo Bike::WHEELS;

A 2

B null

C Error: Cannot override constant

D 4

💡 Hint

Subclass constants can override parent constants.

Bike class overrides WHEELS constant with 2, so Bike::WHEELS outputs 2.

❓ Predict Output

advanced

Output of accessing constant with self and static

What is the output of this PHP code?

PHP

<?php
class ParentClass {
    const VALUE = 'Parent';
    public static function showSelf() {
        echo self::VALUE;
    }
    public static function showStatic() {
        echo static::VALUE;
    }
}
class ChildClass extends ParentClass {
    const VALUE = 'Child';
}
ChildClass::showSelf();
ChildClass::showStatic();

A ChildParent

B ChildChild

C ParentParent

D ParentChild

💡 Hint

self:: uses the class where method is defined; static:: uses called class.

self::VALUE refers to ParentClass::VALUE ('Parent'), static::VALUE refers to ChildClass::VALUE ('Child').

❓ Predict Output

advanced

Output of accessing class constant via object

What will this code output?

PHP

<?php
class Animal {
    const SOUND = 'Roar';
}
$animal = new Animal();
echo $animal::SOUND;

A Roar

B Error: Cannot access constant via object

C SOUND

D null

💡 Hint

Since PHP 5.3, you can access constants via object with :: operator.

Using $animal::SOUND accesses the constant SOUND of class Animal and outputs 'Roar'.

❓ Predict Output

expert

Output of constant expression with magic constant

What is the output of this PHP code?

PHP

<?php
class Test {
    const FILE = __FILE__;
    public static function showFile() {
        echo self::FILE;
    }
}
Test::showFile();

A Error: Cannot use magic constant in class constant

B __FILE__

C The full path and filename of the file where this code is saved

D null

💡 Hint

__FILE__ is a magic constant that gives the current file path.

Class constant FILE is assigned the magic constant __FILE__, which contains the full path of the current file.