Can someone say me because no one recommends Java? D:
I also made some good experiences with (Lwjgl), Slick.
Java should be slow I heard, but is Java really that bad?
Java is actually not as slow as many state. Of course, you have levels of abstraction, and there is automated garbage collection, but these can be pushed into positives rather than negatives. If someone is telling you Java is 'too slow' then they 1.) Don't know how to tune the JVM and 2.) Are probably so low level that they'll only be able to talk about pointers.
Java is used in enterprise software for many high performance utilities, and is chosen because on a server it can be very effective and development is rapid with the numerous amounts of tools and support from other companies.
Of course though there are downsides. Some companies don't keep their tools up to date, and the employees are then forced to use outdated software to develop in. Is that Java's fault? Not as much though as the employer (hints to an anecdote deep inside my career)