Understanding Abstract Classes and Abstract Methods

<?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";

?>