HelloWorldController.php

<?php

namespace Drupal\hello_world\Controller;

use Drupal\Core\Controller\ControllerBase;
use Drupal\hello_world\HelloWorldSalutation;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
* Controller for the salutation message.
*/
class HelloWorldController extends ControllerBase {

 /**
  * The salutation service.
  *
  * @var \Drupal\hello_world\HelloWorldSalutation
  */
 protected $salutation;

 /**
  * HelloWorldController constructor.
  *
  * @param \Drupal\hello_world\HelloWorldSalutation $salutation
  *   The salutation service.
  */
 public function __construct(HelloWorldSalutation $salutation) {
   $this->salutation = $salutation;
 }

 /**
  * {@inheritdoc}
  */
 public static function create(ContainerInterface $container) {
   return new static(
     $container->get('hello_world.salutation')
   );
 }

 /**
  * Hello World.
  *
  * @return array
  *   Our message.
  */
 public function helloWorld() {
   return [
     '#markup' => $this->salutation->getSalutation(),
   ];
 }

}