code: public final static List<PolymerNotation> getPeptidePolymers(List<PolymerNotation> polymers) {
      List<PolymerNotation> peptidePolymers = new ArrayList<PolymerNotation>();
      for (PolymerNotation polymer : polymers) {
        if (polymer.getPolymerID() instanceof PeptideEntity) {
          peptidePolymers.add(polymer);
        }
      }
      return peptidePolymers;
    }
docs: method to get all peptide polymers given a list of PolymerNotation objects
  
  @param polymers List of PolymerNotation objects
  @return list of peptide polymers