​

class DescendingOrder implements Comparator<Integer> {

    public int compare(Integer o1, Integer o2) {

        if(o1 instanceof Comparable && o2 instanceof Comparable) {

            Integer c1 = (Integer)o1;

            Integer c2 = (Integer)o2;

            return c2.compareTo(c1);

        }

        return -1;

    }

}

​

public class prog {

    public static void main(String[] args) {

        TreeSet<Integer> ts = new TreeSet<Integer>(new DescendingOrder());

        ts.add(30);

        ts.add(40);

        ts.add(20);

        ts.add(10);

        Iterator<Integer> iter = ts.iterator();

        while(iter.hasNext()) {

            System.out.println(iter.next());

        }

    }

}