code: @GwtCompatible(serializable = true)
    public <U extends T> Ordering<U> compound(Comparator<? super U> secondaryComparator) {
      return new CompoundOrdering<U>(this, checkNotNull(secondaryComparator));
    }
docs: Returns an ordering which first uses the ordering {@code this}, but which in the event of a
  "tie", then delegates to {@code secondaryComparator}. For example, to sort a bug list first by
  status and second by priority, you might use {@code byStatus.compound(byPriority)}. For a
  compound ordering with three or more components, simply chain multiple calls to this method.
  
  <p>An ordering produced by this method, or a chain of calls to this method, is equivalent to
  one created using {@link Ordering#compound(Iterable)} on the same component comparators.
  
  <p><b>Java 8 users:</b> Use {@code thisComparator.thenComparing(secondaryComparator)} instead.
  Depending on what {@code secondaryComparator} is, one of the other overloads of {@code
  thenComparing} may be even more useful.