title: libgdx user data classes
body: <p>I'm learning libgdx and I've come across a tutorial that made UserData classes for all actors in the game, for  example for an actor, player, he made a class PlayerUserData that extended UserData which is an abstract class that had one method called getUserData which returned an enum indicating what kind of actor it was (ground, player, ...). In the tutorial he explained that he made it to store information and that it would be useful for collisions. I don't fully understand this, why wouldn't you store the information in the actor class of the actor? And what information does it have about collisions?</p>