code: private boolean checkAllRingAtomsHasCoordinates(IAtomContainer ac) {
          for (int i = 0; i < ac.getAtomCount(); i++) {
              if (ac.getAtom(i).getPoint3d() != null && ac.getAtom(i).getFlag(CDKConstants.ISINRING)) {
              } else if (!ac.getAtom(i).getFlag(CDKConstants.ISINRING)) {
              } else {
                  return false;
              }
          }
          return true;
      }
docs: Returns the largest (number of atoms) ring set in a molecule.
  
  @param  ac  AtomContainer
  @return     boolean