code: @Override
      public int getMonomerCount() {
          Iterator<String> keys = strands.keySet().iterator();
          int number = 0;
  
          if (!keys.hasNext()) // no strands
              return super.getMonomerCount();
  
          while (keys.hasNext()) {
              Strand tmp = (Strand) strands.get(keys.next()); // Cast exception?!
              number += (tmp.getMonomers()).size() - 1;
          }
          return number;
      }
docs: Returns the number of monomers present in BioPolymer.
  
  @return number of monomers