code: @Override
      public void addAtom(IAtom oAtom, IStrand oStrand) {
  
          int atomCount = super.getAtomCount();
  
          // Add atom to AtomContainer
          super.addAtom(oAtom);
  
          if (atomCount != super.getAtomCount() && oStrand != null) { // Maybe better to throw null pointer exception here, so user realises that
                                                                      // Strand == null and Atom only gets added to this BioPolymer, but not to a Strand.
              oStrand.addAtom(oAtom);
              if (!strands.containsKey(oStrand.getStrandName())) {
                  strands.put(oStrand.getStrandName(), oStrand);
              }
          }
          /*
           * notifyChanged() is called by addAtom in AtomContainer
           */
      }
docs: Adds the atom oAtom to a specified Strand, whereas the Monomer is unspecified. Hence
  the atom will be added to a Monomer of type UNKNOWN in the specified Strand.
  
  @param oAtom   The atom to add
  @param oStrand The strand the atom belongs to