Properties and visibility in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code with private property?

Consider this PHP class with a private property. What will be the output when trying to access the private property directly from outside the class?

PHP

<?php
class Box {
    private $content = 'secret';
}
$box = new Box();
echo $box->content;
?>

A Fatal error: Uncaught Error: Cannot access private property Box::$content

B null

C secret

D Warning: Undefined property: Box::$content

💡 Hint

Private properties cannot be accessed directly outside the class.

In PHP, private properties are only accessible inside the class itself. Trying to access them from outside causes a fatal error.

❓ Predict Output

intermediate

What will this PHP code output when accessing a protected property from a subclass?

Look at this PHP code where a subclass tries to access a protected property from its parent. What is the output?

PHP

<?php
class Animal {
    protected $type = 'mammal';
}
class Dog extends Animal {
    public function getType() {
        return $this->type;
    }
}
$dog = new Dog();
echo $dog->getType();
?>

A Warning: Undefined property: Dog::$type

B Fatal error: Cannot access protected property Animal::$type

C null

D mammal

💡 Hint

Protected properties are accessible in subclasses.

Protected properties can be accessed inside the class and its subclasses, so the method returns 'mammal'.

🔧 Debug

advanced

Why does this PHP code cause an error when accessing a static private property?

This PHP code tries to access a private static property from a subclass. What error occurs and why?

PHP

<?php
class ParentClass {
    private static $count = 0;
    public static function increment() {
        self::$count++;
    }
    public static function getCount() {
        return self::$count;
    }
}
class ChildClass extends ParentClass {
    public static function increment() {
        self::$count++;
    }
}
ChildClass::increment();
echo ChildClass::getCount();
?>

A Fatal error: Uncaught Error: Access to undeclared static property ChildClass::$count

B 1

C 0

D Warning: Undefined property: ChildClass::$count

💡 Hint

Private static properties are not accessible in subclasses.

Private static properties belong only to the class where they are declared. The subclass cannot access ParentClass::$count, causing a fatal error.

📝 Syntax

advanced

Which option correctly declares a public property with a default value in PHP 8.1+?

Choose the correct syntax to declare a public property with a default value in a PHP class using typed properties.

A public $name: string = 'John';

B public string $name = 'John';

C public string $name: 'John';

D public $name = string 'John';

💡 Hint

Typed properties use type before the variable name with an equals sign for default.

In PHP 7.4+, typed properties are declared as 'public string $name = "John";'. Other options have invalid syntax.

🚀 Application

expert

How many properties are accessible from outside the class in this PHP code?

Given this PHP class with different visibility properties, how many properties can be accessed directly from an instance outside the class?

PHP

<?php
class Car {
    public $make = 'Toyota';
    protected $model = 'Corolla';
    private $year = 2020;
}
$car = new Car();
// How many properties can be accessed directly like $car->property ?
?>

A 0

B 2

C 1

D 3

💡 Hint

Only public properties are accessible from outside the class.

Only the public property $make can be accessed directly. Protected and private properties are not accessible outside the class.