Abstract classes and methods in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of abstract class method call

What is the output of this PHP code?

PHP

<?php
abstract class Animal {
    abstract public function sound();

    public function describe() {
        return "This animal says: " . $this->sound();
    }
}

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

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

A This animal says: sound

B Fatal error: Cannot instantiate abstract class Animal

C Woof

D This animal says: Woof

💡 Hint

Look at how the describe method uses the abstract sound method implemented in the subclass.

The abstract class Animal defines an abstract method sound and a concrete method describe that calls sound. The subclass Dog implements sound returning "Woof". So calling describe on a Dog instance returns "This animal says: Woof".

❓ Predict Output

intermediate

What error occurs when instantiating an abstract class?

What happens when you run this PHP code?

PHP

<?php
abstract class Vehicle {
    abstract public function move();
}

$car = new Vehicle();
?>

A No output, code runs fine

B Fatal error: Cannot instantiate abstract class Vehicle

C Parse error: syntax error, unexpected 'abstract'

D Warning: Abstract method move() not implemented

💡 Hint

Remember, abstract classes cannot be directly created as objects.

Abstract classes cannot be instantiated directly. Trying to create an object of an abstract class causes a fatal error.

🔧 Debug

advanced

Identify the error in abstract method implementation

What error will this PHP code produce?

PHP

<?php
abstract class Shape {
    abstract public function area();
}

class Circle extends Shape {
    public function area($radius) {
        return 3.14 * $radius * $radius;
    }
}

$circle = new Circle();
echo $circle->area(5);
?>

A Fatal error: Declaration of Circle::area($radius) must be compatible with Shape::area()

B Output: 78.5

C Parse error: syntax error, unexpected '$radius'

D Warning: Missing argument for area()

💡 Hint

Check if the method signatures match exactly between abstract and subclass methods.

The abstract method area in Shape has no parameters. The subclass Circle defines area with a parameter $radius. PHP requires the subclass method to have the same signature, so this causes a fatal error.

📝 Syntax

advanced

Which code snippet correctly defines an abstract class with an abstract method?

Choose the correct PHP code that defines an abstract class with one abstract method run.

A

<?php
abstract class Runner {
    abstract public function run();
}
?>

B

<?php
class Runner {
    abstract public function run();
}
?>

C

<?php
abstract class Runner {
    public abstract function run() {}
}
?>

D

<?php
abstract class Runner {
    abstract function run() {}
}
?>

💡 Hint

Remember abstract methods cannot have a body and must be inside an abstract class.

Option A correctly defines an abstract class Runner with an abstract method run without a body. Option A is invalid because abstract methods must be inside abstract classes. Options C and D incorrectly provide a method body for the abstract method, which is not allowed.

🚀 Application

expert

How many methods must be implemented?

Given this PHP code, how many methods must the class Smartphone implement to avoid errors?

PHP

<?php
abstract class Device {
    abstract public function powerOn();
    abstract public function powerOff();
    public function reset() {
        $this->powerOff();
        $this->powerOn();
    }
}

abstract class Phone extends Device {
    abstract public function call($number);
}

class Smartphone extends Phone {
    public function powerOn() {
        echo "Powering on";
    }

    public function powerOff() {
        echo "Powering off";
    }

    // Missing call method implementation
}
?>

A 3

B 2

C 1

D 0

💡 Hint

Count all abstract methods from parent classes that are not yet implemented.

The abstract class Device has two abstract methods: powerOn and powerOff, both implemented in Smartphone. The abstract class Phone adds one abstract method: call, which Smartphone has not implemented yet. So Smartphone must implement exactly one more method: call.