code: protected boolean isTheSame(IIsotope isotopeOne, IIsotope isotopeTwo) {
  
          if (!Objects.equals(isotopeOne.getMassNumber(),
                              isotopeTwo.getMassNumber()))
              return false;
  
          Double natAbund1 = isotopeOne.getNaturalAbundance();
          Double natAbund2 = isotopeTwo.getNaturalAbundance();
  
          Double exactMass1 = isotopeOne.getExactMass();
          Double exactMass2 = isotopeTwo.getExactMass();
  
          if (natAbund1 == null) natAbund1 = -1.0;
          if (natAbund2 == null) natAbund2 = -1.0;
          if (exactMass1 == null) exactMass1 = -1.0;
          if (exactMass2 == null) exactMass2 = -1.0;
  
          if (!isotopeOne.getSymbol().equals(isotopeTwo.getSymbol())) return false;
          if (natAbund1.doubleValue() != natAbund2) return false;
          return exactMass1.doubleValue() == exactMass2;
      }
docs: Compare to IIsotope. The method doesn't compare instance but if they
  have the same symbol, natural abundance and exact mass.
  
  @param isotopeOne   The first Isotope to compare
  @param isotopeTwo   The second Isotope to compare
  @return             True, if both isotope are the same