Journalism will focus mostly on just writing and Australian media subjects, whereas in communications you will have the opportunity to study public relations and advertising subjects as well. So one is just a more narrow version of the other with potentially slightly more emphasis on print communication to the mass audience.
I would recommend starting off with the foundation subjects and seeing what you like first, as you don't have to choose a major until second year. A lot of universities combine the two fields into one major. But in this climate I would probably choose communications - you will still have the chance to do Journalism subjects but you won't be as limited (which is important because journalism is a very difficult field to get a job in and it's only going to get harder).