Drupal 8 has switched from PSR-0 to PSR-4. PSR is an autoloading standard, that ensures, that all classes files get loaded properly, without having to load the class files manually. PSR-4 is the latest version of the PSR standard, that allows to have a shorter class file folder hierarchy, correcting the unpleasant issue of many layers of folders in the early PSR versions.
The declaration in the routing file remains the same, like:
However, the folder path of the class file has now changed. Taking example of my Angular JS Sample module.