Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

<?php
abstract class Shape
{
    public function __construct(protected string $color = 'black') {}

// Subclasses MUST implement these
    abstract public function area(): float;
    abstract public function perimeter(): float;

// Concrete method — shared by all shapes
    public function describe(): string
    {
        return sprintf(
            '%s %s — Area: %.2f, Perimeter: %.2f',
            ucfirst($this->color),
            static::class,      // late static binding
            $this->area(),
            $this->perimeter()
        );
    }
}

class Circle extends Shape
{
    public function __construct(private float $radius, string $color = 'red')
    {
        parent::__construct($color);
    }

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

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

class Rectangle extends Shape
{
    public function __construct(
        private float $width,
        private float $height,
        string $color = 'blue'
    ) {
        parent::__construct($color);
    }

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

$shapes = [new Circle(5), new Rectangle(4, 6)];
foreach ($shapes as $shape) {
    echo $shape->describe() . "
";
}

// new Shape(); // Fatal Error: Cannot instantiate abstract class