Understanding Abstract Classes and Abstract Methods | CodeSignal Learn

Understanding Abstract Classes and Abstract Methods | CodeSignal Learn

Abstract classes and abstract methods are essential when you want to define a common interface for a group of derived classes. They ensure that derived classes implement specific methods, enabling you to write more robust and scalable programs.

Let's revisit some of the key concepts through the following PHP code example:

PHP

<?php

// Define an abstract class Shape. 
abstract class Shape {
    // Abstract method for calculating the area
    abstract public function area(): float;

    // Abstract method for calculating the perimeter
    abstract public function perimeter(): float;
}

// Define a Circle class that inherits from Shape
class Circle extends Shape {
    private $radius;

    // Constructor to initialize the radius
    public function __construct(float $radius) {
        $this->radius = $radius;
    }

    // Implement the area and perimeter methods
    public function area(): float {
        return 3.14 * $this->radius * $this->radius;
    }

    public function perimeter(): float {
        return 2 * 3.14 * $this->radius;
    }
}

// Define a Rectangle class that inherits from Shape
class Rectangle extends Shape {
    private $width;
    private $height;

    // Constructor to initialize the width and height
    public function __construct(float $width, float $height) {
        $this->width = $width;
        $this->height = $height;
    }

    // Implement the area and perimeter methods
    public function area(): float {
        return $this->width * $this->height;
    }

    public function perimeter(): float {
        return 2 * ($this->width + $this->height);
    }
}

$circle = new Circle(5);
$rectangle = new Rectangle(4, 6);

echo "Circle Area: " . $circle->area() . ", Perimeter: " . $circle->perimeter() . "\n";
echo "Rectangle Area: " . $rectangle->area() . ", Perimeter: " . $rectangle->perimeter() . "\n";

// Using Shape type to reference a Circle object
$shape = new Circle(3);
echo "Shape Area: " . $shape->area() . ", Perimeter: " . $shape->perimeter() . "\n";

?>

In this example, we define an abstract class Shape with two abstract methods: area and perimeter. Derived classes such as Circle and Rectangle implement these methods.

Let's now understand the abstract class and abstract methods in more detail:

An abstract class is a class that contains at least one abstract method — a method declared with the abstract keyword and without implementation. An abstract class cannot be instantiated, but it can be used as a base class for other classes. In the example above, Shape is an abstract class.

The derived classes Circle and Rectangle inherit from the abstract class Shape. They must implement the abstract methods area and perimeter to provide concrete implementations. If a derived class does not implement all the abstract methods, it will also be considered an abstract class and cannot be instantiated.