Dependency Injection

Dependency Injection was introduced in Joomla 4 to try to enable better testing of the Joomla code. If you're not familiar with the concepts of dependency injection then you may find the following videos useful: Dependency Injection in PHP and DI Container. The videos are not related to Joomla, but do present good background information.

There are also a couple of Joomla-related videos, covering Joomla 4 Dependency Injection and services/provider.php.