PHP框架中的设计模式应用：提高代码可复用性和易维护性

class Database
{
    private static $instance;

    private function __construct() {}

    public static function getInstance()
    {
        if (!isset(self::$instance)) {
            self::$instance = new Database();
        }

        return self::$instance;
    }
}

// 使用单例
$db = Database::getInstance();

class BikeFactory
{
    public static function createBike($type)
    {
        switch ($type) {
            case 'road':
                return new RoadBike();
            case 'mountain':
                return new MountainBike();
            default:
                throw new Exception('Invalid bike type');
        }
    }
}

// 使用工厂创建对象
$roadBike = BikeFactory::createBike('road');

class Adaptee
{
    public function oldMethod()
    {
        // 这是需要被适配的旧方法
    }
}

class Adapter implements AdapteeInterface
{
    private $adaptee;

    public function __construct(Adaptee $adaptee)
    {
        $this->adaptee = $adaptee;
    }

    public function newMethod()
    {
        $this->adaptee->oldMethod();
    }
}

// 使用适配器
$adaptee = new Adaptee();
$adapter = new Adapter($adaptee);
$adapter->newMethod();