code: public static IDifference difference(IChemObject first, IChemObject second) {
          if (!(first instanceof ISingleElectron && second instanceof ISingleElectron)) {
              return null;
          }
          ISingleElectron firstB = (ISingleElectron) first;
          ISingleElectron secondB = (ISingleElectron) second;
          IDifferenceList totalDiff = new ChemObjectDifference("SingleElectronDiff");
          totalDiff.addChild(AtomDiff.difference(firstB.getAtom(), secondB.getAtom()));
          totalDiff.addChild(ElectronContainerDiff.difference(first, second));
          if (totalDiff.childCount() > 0) {
              return totalDiff;
          } else {
              return null;
          }
      }
docs: Compare two {@link IChemObject} classes and return the difference as an {@link IDifference}.
  
  @param first  the first of the two classes to compare
  @param second the second of the two classes to compare
  @return an {@link IDifference} representation of the difference between the first and second {@link IChemObject}.