code: @Override
      public void addMapping(IMapping mapping) {
          if (mappingCount + 1 >= map.length) growMappingArray();
          map[mappingCount] = mapping;
          mappingCount++;
          notifyChanged();
      }
docs: Adds a mapping between the reactant and product side to this
  Reaction.
  
  @param mapping Mapping to add.
  @see   #mappings