Extending classes in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of extended class method call

What is the output of this PHP code?

PHP

<?php
class Animal {
    public function sound() {
        return "Some sound";
    }
}

class Dog extends Animal {
    public function sound() {
        return "Bark";
    }
}

$dog = new Dog();
echo $dog->sound();
?>

A Some sound

B Fatal error: Cannot redeclare method

C Bark

D null

💡 Hint

Remember, when a child class defines a method with the same name as the parent, it overrides it.

The Dog class extends Animal and overrides the sound() method. So calling sound() on a Dog object returns "Bark".

❓ Predict Output

intermediate

Output when calling parent method from child

What will this PHP code output?

PHP

<?php
class Vehicle {
    public function start() {
        return "Vehicle started";
    }
}

class Car extends Vehicle {
    public function start() {
        return parent::start() . " and car is ready";
    }
}

$car = new Car();
echo $car->start();
?>

A Car started

B Vehicle started and car is ready

C Vehicle started

D Fatal error: Call to undefined method

💡 Hint

Look at how parent::start() is used inside the child method.

The Car class calls the parent start() method and appends additional text. So the output is "Vehicle started and car is ready".

❓ Predict Output

advanced

Output when child defines method same as parent's private

What is the output of this PHP code?

PHP

<?php
class Fruit {
    private function taste() {
        return "Sweet";
    }
}

class Apple extends Fruit {
    public function taste() {
        return "Sour";
    }
}

$apple = new Apple();
echo $apple->taste();
?>

A Sour

B Sweet

C Fatal error: Call to private method Fruit::taste() from context

D Fatal error: Cannot override private method

💡 Hint

Private methods are not inherited or overridable; child can define its own method with the same name.

The taste() method in Fruit is private and not inherited. Apple defines its own independent taste() method, which is called and outputs "Sour". No error occurs.

📝 Syntax

advanced

Which code causes a syntax error in class extension?

Which of the following PHP code snippets will cause a syntax error?

A <?php class A { public function foo() {} } class B extends A { public function foo() { parent.foo(); } } ?>

B <?php class A { public function foo() {} } class B extends A { public function foo() { echo 'Hi'; } } ?>

C <?php class A { public function foo() {} } class B extends A { public function foo() { parent::foo(); } } ?>

D <?php class A { public function foo() {} } class B extends A { public function foo() {} } ?>

💡 Hint

Check how the parent method is called inside the child method.

In PHP, to call a parent method, you must use parent::methodName(). Using parent.methodName() causes a syntax error.

🚀 Application

expert

Determine the number of methods available in child class

Given the following PHP classes, how many methods can be called on an instance of Smartphone?

PHP

<?php
class Device {
    public function powerOn() { return "Powering on"; }
    protected function reset() { return "Resetting"; }
    private function secret() { return "Secret"; }
}

class Phone extends Device {
    public function call() { return "Calling"; }
    protected function reset() { return "Phone reset"; }
}

class Smartphone extends Phone {
    public function browse() { return "Browsing"; }
    private function secret() { return "Smartphone secret"; }
}

$phone = new Smartphone();

A 4

B 6

C 5

D 3

💡 Hint

Count the public methods that can be called directly on a Smartphone instance from outside: powerOn(), call(), browse().

Public methods callable on a Smartphone instance from outside:
- powerOn() (from Device)
- call() (from Phone)
- browse() (from Smartphone)
Protected reset() cannot be called from outside. Private methods are inaccessible. Total: 3.