code: @Override
      public Collection<String> getMonomerNames() {
          Iterator<String> keys = strands.keySet().iterator();
          Map<String, IMonomer> monomers = new Hashtable<String, IMonomer>();
  
          if (!keys.hasNext()) // no strands
              return super.getMonomerNames();
  
          while (keys.hasNext()) {
              Strand oStrand = (Strand) strands.get(keys.next());
              monomers.putAll(oStrand.getMonomers());
          }
          return monomers.keySet();
      }
docs: Returns a collection of the names of all <code>Monomer</code>s in this
  BioPolymer.
  
  @return a <code>Collection</code> of all the monomer names.