How to Reorder SortedSet

Question

I want to print an ordered list on a Map using the following:

Map<Float, String> mylist = new HashMap<>(); mylist.put(10.5, a); mylist.put(12.3, b); mylist.put(5.1, c); SortedSet<Float> orderlist = new TreeSet<Float>(mylist.keySet()); for (Float i : orderlist) { System.out.println(i+" "+mylist.get(i)); } 

The above code prints:

 5.1 c 10.5 a 12.3 b 

But how to print the list of orders in reverse order, as shown below:

 12.3 b 10.5 a 5.1 c 

Answer 1

If you want to save the elements in the SortedSet in the reverse order, the only change you need to make is to build the TreeSet using the appropriate constructor , which the custom Comparator accepts:

 Map<Float, String> mylist = new HashMap<>(); mylist.put(10.5, a); mylist.put(12.3, b); mylist.put(5.1, c); SortedSet<Float> orderlist = new TreeSet<Float>(Collections.reverseOrder()); orderList.addAll(mylist.keySet()); for (Float i : orderlist) { System.out.println(i+" "+mylist.get(i)); } 

Note that the neat method here is Collections.reverseOrder() , which returns a Comparator that compares as opposed to the natural ordering of the elements.

Answer 2

You can also try the following:

  Map<Float, String> mylist = new HashMap<Float, String>(); mylist.put(10.5, a); mylist.put(12.3, b); mylist.put(5.1, c); SortedSet<Float> orderlist = new TreeSet<Float>(mylist.keySet()).descendingSet(); for (Float i : orderlist) { System.out.println(i+" "+mylist.get(i)); } 

Answer 3

Try using NavigableSet :

  public NavigableSet<E> descendingSet() 

Like this:

  SortedSet<Float> orderlist = new TreeSet<Float>(mylist.keySet()); SortedSet<Float> treereverse = new TreeSet<Float>(); // creating reverse set treereverse=(TreeSet)orderlist.descendingSet(); 

Finally, you have a treereverse in reverse order.