code: public RawComparator getOutputKeyComparator() {
      Class<? extends RawComparator> theClass = getClass("mapred.output.key.comparator.class",
  	        null, RawComparator.class);
      if (theClass != null)
        return ReflectionUtils.newInstance(theClass, this);
      return WritableComparator.get(getMapOutputKeyClass().asSubclass(WritableComparable.class));
    }
docs: Get the {@link RawComparator} comparator used to compare keys.
  
  @return the {@link RawComparator} comparator used to compare keys.