Oh and agian, SRS. I'm not sure where you are with coding but my own preffered package for (non Android) Java is Netbeans. For Android though, you would probably want to look here my own Android set up atm is an earlier Eclipse based one.

It's all (at least with the ones I've used) very good free stuff. The only place I think a cost   becomes mandatory is to publish on the Play store. You have to pay for and sign up to some sort of developer licence for that.