Mac because you can run the full version of windows 7 in Bootcamp, and you still can also use the mac side. So if you buy a mac, you buy 2 operating systems
well if you're programming in java then you probably want to get a win7 pc with good specs and ram. you really don't need java for ios apps because they use Objective-c and that's a bit different than java. but if you were to want to program ios apps definitely get the mac because it comes with just about everything you need to start. or dual boot(best option.)