PHP找不到类

Silly question, but I cannot figure out what's wrong. I have a ready to use script that prompts a fatal error when I run it.

use DDelivery\Order\DDeliveryOrder;
use DDelivery\Order\DDeliveryProduct;
use DDelivery\Order\DDStatusProvider;

class IntegratorShop extends \DDelivery\Adapter\PluginFilters {
...

The error is:

Fatal error: Class 'DDelivery\Adapter\PluginFilters' not found in .../ddelivery/IntegratorShop.php on line 40

Frankly I never used 'use' declaration before, so it's hard to tell what's wrong. I'm sure it is something obvious. Thanks!

Try below code.

use DDelivery\Order\DDeliveryOrder;
use DDelivery\Order\DDeliveryProduct;
use DDelivery\Order\DDStatusProvider;
use DDelivery\Adapter\PluginFilters;


class IntegratorShop extends PluginFilters {
.....