text: public NavigableSet<E> subSet(E start, boolean startInclusive, E end,boolean endInclusive) {Comparator<? super E> c = backingMap.comparator();int compare = (c == null) ? ((Comparable<E>) start).compareTo(end) : c.compare(start, end);if (compare <= 0) {return new TreeSet<E>(backingMap.subMap(start, startInclusive, end,endInclusive));}throw new IllegalArgumentException();}