code: @Override
      public IReaction getReaction(int position) {
  
          if (!hashMapChain.containsValue(position)) return null;
  
          Set<Entry<IReaction, Integer>> entries = hashMapChain.entrySet();
          for (Iterator<Entry<IReaction, Integer>> it = entries.iterator(); it.hasNext();) {
              Entry<IReaction, Integer> entry = it.next();
              if (entry.getValue().equals(position)) return entry.getKey();
          }
  
          return null;
      }
docs: Get the reaction of this chain reaction object at the position.
  
  @param  position The position of the IReaction in this chain to look for
  @return          Reaction The IReaction to look at