code: public static IRing getMostComplexRing(IRingSet ringSet) {
          int[] neighbors = new int[ringSet.getAtomContainerCount()];
          IRing ring1, ring2;
          IAtom atom1, atom2;
          int mostComplex = 0, mostComplexPosition = 0;
          /* for all rings in this RingSet */
          for (int i = 0; i < ringSet.getAtomContainerCount(); i++) {
              /* Take each ring */
              ring1 = (IRing) ringSet.getAtomContainer(i);
              /*
               * look at each Atom in this ring whether it is part of any other
               * ring
               */
              for (int j = 0; j < ring1.getAtomCount(); j++) {
                  atom1 = ring1.getAtom(j);
                  /* Look at each of the other rings in the ringset */
                  for (int k = i + 1; k < ringSet.getAtomContainerCount(); k++) {
                      ring2 = (IRing) ringSet.getAtomContainer(k);
                      if (ring1 != ring2) {
                          for (int l = 0; l < ring2.getAtomCount(); l++) {
                              atom2 = ring2.getAtom(l);
                              if (atom1.equals(atom2)) {
                                  neighbors[i]++;
                                  neighbors[k]++;
                                  break;
                              }
                          }
                      }
                  }
              }
          }
          for (int i = 0; i < neighbors.length; i++) {
              if (neighbors[i] >= mostComplex) {
                  mostComplex = neighbors[i];
                  mostComplexPosition = i;
              }
          }
          return (IRing) ringSet.getAtomContainer(mostComplexPosition);
      }
docs: Returns the ring with the highest numbers of other rings attached to it. If an
  equally complex ring is found the last one is selected allow prioritization by
  size with {@link RingSetManipulator#sort(IRingSet)}.
  
  @param ringSet The collection of rings
  @return the ring with the highest numbers of other rings attached to it.