Before we go and use our service in the Controller we created, let's take a breather and run through the ways you can make use of services once they are registered.
There are essentially two ways--statically and injected. The first is done by a static call to the Service Container, whereas the second uses dependency injection to pass the object through the constructor (or in some rare cases, a setter method). However, let's check out how, why, and what is the real difference.
Statically, you would use the global Drupal class to instantiate a service:
$service = \Drupal::service('hello_world.salutation');
This is how we use services in the .module files and classes, which are not exposed to the Service Container and into which we cannot inject--although the latter instances are rare. A few popular services also have shorthand methods...
