PHP オブジェクト指向の単純なファクトリ パターンを通じてオブジェクトのカプセル化と隠蔽を実装する方法

<?php
abstract class Shape {
    protected $color;

    abstract public function draw();
}
?>

<?php
class Circle extends Shape {
    private $radius;

    public function __construct($radius, $color) {
        $this->radius = $radius;
        $this->color = $color;
    }

    public function draw() {
        echo "Drawing a ".$this->color." circle with radius ".$this->radius.".<br>";
    }
}

class Square extends Shape {
    private $length;

    public function __construct($length, $color) {
        $this->length = $length;
        $this->color = $color;
    }

    public function draw() {
        echo "Drawing a ".$this->color." square with length ".$this->length.".<br>";
    }
}
?>

<?php
class ShapeFactory {
    public static function create($type, $params) {
        switch ($type) {
            case 'circle':
                return new Circle($params['radius'], $params['color']);
            case 'square':
                return new Square($params['length'], $params['color']);
            default:
                throw new Exception('Invalid shape type.');
        }
    }
}
?>

<?php
$params = [
    'radius' => 5,
    'color' => 'red'
];

$circle = ShapeFactory::create('circle', $params);
$circle->draw();

$params = [
    'length' => 10,
    'color' => 'blue'
];

$square = ShapeFactory::create('square', $params);
$square->draw();
?>