Either in ring itself (which means a change to the IRing interface) or in RingManipulator. There is such a method in o.o.c.render.generators.RingGenerator called 'ringIsAromatic'.
Oh, I just found AromaticityCalculator, and its isAromatic(IRing, IAtomContainer):boolean method....
However, that code is doing something more complex (checking for electrons and such), rather than just testing for ISAROMATIC flags. So I'm not sure now...
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Oh, I just found AromaticityCalculator, and its isAromatic(IRing, IAtomContainer):boolean method....
However, that code is doing something more complex (checking for electrons and such), rather than just testing for ISAROMATIC flags. So I'm not sure now...