For one, you really shouldn't use the == operators for that. It will work for now, just because the game returns the same instance every time, but it won't work if you start to save them in a file, for example. For another, I hope "dAPI" isn't the name of the class. If it is, read this. Also, "dAPI.getInstance().getUUID(player)" is not in any way shorter than player.getUniqueId(). Actually, now that I look at it, does that method return a string? If so, that == comparison is probably going to fail. You shouldn't do that, or, if you're going to do that (for no valid reason), you should use .equals(). But you can just store the UUIDs inside the lists. And this is why you should also always provide full code, now I'm not really sure if that's the problem or not.