code: public IRingSet getLargestRingSet(List<IRingSet> ringSystems) {
          IRingSet       largestRingSet = null;
          int            atomNumber     = 0;
          IAtomContainer container      = null;
          for (int i = 0; i < ringSystems.size(); i++) {
              container = getAllInOneContainer(ringSystems.get(i));
              if (atomNumber < container.getAtomCount()) {
                  atomNumber = container.getAtomCount();
                  largestRingSet = ringSystems.get(i);
              }
          }
          return largestRingSet;
      }
docs: Returns the largest (number of atoms) ring set in a molecule.
  
  @param ringSystems RingSystems of a molecule
  @return The largestRingSet