code: @Override
      public ISingleElectron getSingleElectron(int idx) {
          if (idx < 0 || idx >= singleElectronCount)
              throw new IndexOutOfBoundsException("Single Electrong index out of bounds: 0 <= " + idx + " < " + singleElectronCount);
          return singleElectrons[idx];
      }
docs: {@inheritDoc}