code: public static WritableComparator get(Class<? extends WritableComparable> c) {
          WritableComparator comparator = comparators.get(c);
          if (comparator == null) {
              // force the static initializers to run
              forceInit(c);
              // look to see if it is defined now
              comparator = comparators.get(c);
              // if not, use the generic one
              if (comparator == null) {
                  comparator = new WritableComparator(c, true);
              }
          }
          return comparator;
      }
docs: Get a comparator for a {@link WritableComparable} implementation.