I created new classes by right clicking on a package. The package seems correct in the actual code in the classes, but the new classes can't be seen in the package in the Project Explorer.
What's going on?
Yes, the problem was that some processes, needed for updating the project explorer, in Eclipse were frozen and even quitting Eclipse wasn't possible without using Task Manager to destroy the Eclipse-process. Only after restarting my Windows 8 system I was able to continue using Eclipse normally.