service

use Drupal\user\UserDataInterface;

/**
 * The user data service.
 */
protected UserDataInterface $userData;

/**
 * Constructs the object.
 *
 * @param \Drupal\user\UserDataInterface $user_data
 *   The user data service.
 */
public 

$moduleHandler = \Drupal::service('module_handler');
if ($moduleHandler->moduleExists('my_module')) {
 // Code Here.
}

use Drupal\file\FileUsage\DatabaseFileUsageBackend;

 /**
 * File usage service.
 */
protected DatabaseFileUsageBackend $fileUsage;

/**
 * Constructs an object.
 *
 * @param \Drupal\file\FileUsage\DatabaseFileUsageBackend $file_usage
 *   File usage service.
 */

/** @var \Drupal\privatemsg\PrivateMsgService $privatemsg_service */
$privatemsg_service = \Drupal::service('privatemsg.common');