code: public void incrementCounts(Collection<E> keys, int count) {
      for (E key : keys) {
        incrementCount(key, count);
      }
    }
docs: Adds the given count to the current counts for each of the given keys.
  If any of the keys haven't been seen before, they are assumed to have
  count 0, and thus this method will set their counts to the given
  amount. Negative increments are equivalent to calling <tt>decrementCounts</tt>.
  <p/>
  To more conveniently increment the counts of a collection of objects by
  1, use {@link #incrementCounts(Collection)}.
  <p/>
  To set the counts of a collection of objects to a specific value instead
  of incrementing them, use {@link #setCounts(Collection,int)}.