设计模式之空对象模式(php实现)

/** * 在空对象模式（Null Object Pattern）中，一个空对象取代 NULL 对象实例的检查。 * Null 对象不是检查空值，而是反应一个不做任何动作的关系。这样的 Null 对象也可以在数据不可用的时候提供默认的行为。 * 在空对象模式中，我们创建一个指定各种要执行的操作的抽象类和扩展该类的实体类，还创建一个未对该类做任何实现的空对象类，该空对象类将无缝地使用在需要检查空值的地方。 */

<?phpnamespace NullObject;abstract class AbstractCustomer{ ???protected $name; ???public abstract function isNil():bool; ???public abstract function getName() : string;}

<?phpnamespace NullObject;class RealCustomer extends AbstractCustomer{ ???public function __construct(string $name) ???{ ???????$this->name = $name; ???} ???????public function isNil():bool ???{ ???????return false; ???} ???public function getName() : string ???{ ???????return $this->name; ???}}

<?phpnamespace NullObject;class NullCustomer extends AbstractCustomer{ ???public function getName() : string ???{ ???????return "Not Available in Customer Database"; ???} ???public function isNil():bool ???{ ???????return true; ???}}

<?phpnamespace NullObject;class CustomerFactory{ ???public static $users = []; ???public static function getCustomer($name) ???{ ???????if (in_array($name, self::$users)){ ???????????return new RealCustomer($name); ???????} ???????return new NullCustomer(); ???}}

<?phpspl_autoload_register(function ($className){ ???$className = str_replace(‘\\‘,‘/‘,$className); ???include $className.".class.php";});use NullObject\CustomerFactory;CustomerFactory::$users = ["Rob", "Joe", "Julie"];$customer1 = CustomerFactory::getCustomer(‘Rob‘);$customer2 = CustomerFactory::getCustomer(‘Bob‘);$customer3 = CustomerFactory::getCustomer(‘Joe‘);$customer4 = CustomerFactory::getCustomer(‘Julie‘);echo $customer1->getName();echo ‘<br/>‘;echo $customer2->getName();echo ‘<br/>‘;echo $customer3->getName();echo ‘<br/>‘;echo $customer4->getName();echo ‘<br/>‘;