I apologize for the bump, but I felt it appropriate to add my solution to this problem. This thread is very high on Google when searching for the aforementioned error message.
I recompiled with the flag it suggests and my error came from this "bad" line of code:
ArrayList<JButton> sodaChoices = new ArrayList();
The error disappeared when I wrote this:
ArrayList<JButton> sodaChoices = new ArrayList<JButton>();
Sorry if "bumping" peeved anyone, but what would the internet be if people didn't share knowledge? Hopefully this helps some other poor intro Java student out there like myself