In Joomla 4 we are moving towards a service oriented architecture. This means we are working with a DI container and interfaces. I will explain the benefits, why we we want to leave the ages of static calls behind us and how all of that got implemented in a backwards compatible way.
In 2007 published Allon Moritz his first Joomla extension in the JED. It began as hobby and in 2015 did found Allon Moritz the Digital Peak GmbH company (joomla.digital-peak.com) which specializes in Joomla extension development. Allon Moritz, aka laoneo, helps actively in the development of the Joomla CMS on Github. For example the custom fields functionality is done by him. Currently he is a member of the "Production Department Team", leads the media manager team and is porting the Joomla CMS to namespaces in the Joomla 4 working group.