code: private SortKey toggle(SortKey key)
      {
          if (key.getSortOrder() == SortOrder.ASCENDING)
          {
              return new SortKey(key.getColumn(), SortOrder.DESCENDING);
          }
          return new SortKey(key.getColumn(), SortOrder.ASCENDING);
      }
docs: Toggle the given key between ASCENDING and DESCENDING
  
  @param key The key
  @return The new key