Presumably, you were using an O/S with case-insensitive file system (Windows or, under some circumstances, Mac OS X). Under such an O/S, Java compilation typically will work even when you use the "wrong" case.
However, you should get into the habit of using the "right" case, even on such O/S, so that your files will still work correctly on a case-sensitive file system (e.g. Unix).
Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.