code: @Override
  	public DescriptorValue calculate(ISubstance substance) {
          int count = 0;
          if (substance != null) {
              for (IAtomContainer container : substance.atomContainers()) {
                  for (IAtom atom : container.atoms()) {
                      if ("O".equals(atom.getSymbol()) || 8 == atom.getAtomicNumber())
                          count++;
                  }
              }
          }
  
  		return new DescriptorValue(
  		    getSpecification(), getParameterNames(), getParameters(),
  		    new IntegerResult(count), getDescriptorNames()
  		);
  	}
docs: {@inheritDoc}