Parent keyword behavior in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of parent:: method call in inheritance

What is the output of the following PHP code?

PHP

<?php
class A {
    public function greet() {
        return "Hello from A";
    }
}
class B extends A {
    public function greet() {
        return parent::greet() . " and B";
    }
}
$b = new B();
echo $b->greet();
?>

A Hello from A and B

B Hello from B

C Hello from A

D Fatal error: Cannot access parent::greet()

💡 Hint

Remember that parent:: calls the method from the parent class.

The method greet() in class B calls parent::greet(), which runs the greet() method from class A, returning "Hello from A". Then it concatenates " and B". So the output is "Hello from A and B".

❓ Predict Output

intermediate

Using parent:: in constructor

What will be the output of this PHP code?

PHP

<?php
class ParentClass {
    public function __construct() {
        echo "Parent constructor called. ";
    }
}
class ChildClass extends ParentClass {
    public function __construct() {
        parent::__construct();
        echo "Child constructor called.";
    }
}
new ChildClass();
?>

A Child constructor called.

B Parent constructor called. Child constructor called.

C Parent constructor called.

D Fatal error: Cannot call parent constructor

💡 Hint

Check how constructors are called in inheritance.

The ChildClass constructor calls parent::__construct(), which runs the ParentClass constructor printing "Parent constructor called. ". Then it prints "Child constructor called.". So the full output is "Parent constructor called. Child constructor called.".

❓ Predict Output

advanced

Output when parent method is private

What happens when a child class tries to call a private parent method using parent:: ?

PHP

<?php
class Base {
    private function secret() {
        return "Secret from Base";
    }
    public function reveal() {
        return $this->secret();
    }
}
class Derived extends Base {
    public function secret() {
        return "Secret from Derived";
    }
    public function revealSecret() {
        return parent::secret();
    }
}
$d = new Derived();
echo $d->reveal();
echo " - ";
echo $d->secret();
echo " - ";
echo $d->revealSecret();
?>

A Fatal error - Secret from Derived - Secret from Base

B Secret from Base - Secret from Derived - Secret from Base

C Secret from Base - Secret from Derived - Fatal error

D Secret from Base - Fatal error - Secret from Derived

💡 Hint

Private methods are not accessible via parent:: in child classes.

Base::reveal() calls $this->secret(). Since secret() is private in Base and private methods cannot be overridden, it calls Base's private secret(), returning "Secret from Base". Derived's public secret() is a separate method, so $d->secret() returns "Secret from Derived". parent::secret() from Derived cannot access Base's private method, causing a fatal error. Output: "Secret from Base - Secret from Derived - Fatal error".

❓ Predict Output

advanced

parent:: with static methods and late static binding

What is the output of this PHP code involving static methods and parent::?

PHP

<?php
class Alpha {
    public static function who() {
        return "Alpha";
    }
    public static function test() {
        return static::who();
    }
}
class Beta extends Alpha {
    public static function who() {
        return "Beta";
    }
    public static function test() {
        return parent::test();
    }
}
echo Beta::test();
?>

A BetaBeta

B Alpha

C Fatal error: Cannot access parent::test()

D Beta

💡 Hint

Remember that static:: uses late static binding to call the method in the called class.

Beta::test() calls parent::test(), which is Alpha::test(). Alpha::test() calls static::who(), which uses late static binding and calls Beta::who(), returning "Beta". So the output is "Beta".

❓ Predict Output

expert

Complex parent:: calls with traits and multiple inheritance

What is the output of this PHP code involving traits and parent:: calls?

PHP

<?php
trait T {
    public function say() {
        return "Trait says hi";
    }
}
class Base {
    public function say() {
        return "Base says hi";
    }
}
class Child extends Base {
    use T;
    public function say() {
        return parent::say() . " and " . T::say();
    }
}
$c = new Child();
echo $c->say();
?>

A Fatal error: Cannot access trait method T::say() directly

B Base says hi and Trait says hi

C Trait says hi and Base says hi

D Base says hi

💡 Hint

Traits methods cannot be called statically like T::say() inside an instance method.

Inside Child::say(), parent::say() correctly calls Base::say(). However, T::say() is a trait method and cannot be called statically like that. This causes a fatal error. The correct way would be to call $this->say() carefully or rename methods to avoid conflict.