TreeMap high-low key Integer sort

Question

    Map<Integer, String> map = new TreeMap<Integer, String>();

    // Add Items to the TreeMap
    map.put(new Integer(8), "Eight");
    map.put(new Integer(9), "Nine");
    map.put(new Integer(1), "One");
    map.put(new Integer(4), "Four");
    map.put(new Integer(10), "Ten");
    map.put(new Integer(5), "Five");
    map.put(new Integer(6), "Six");
    map.put(new Integer(2), "Two");
    map.put(new Integer(3), "Three");
    map.put(new Integer(7), "Seven");

    keys = map.keySet();
    for (Iterator i = keys.iterator(); i.hasNext();) {
      Integer key = (Integer) i.next();
      String value = (String) map.get(key);
      System.out.println(key + " = " + value);
    }

Output:

• 1 = One
• 2 = Two
• 3 = Three
• 4 = Four
• 5 = Five
• 7 = Seven
• 8 = Eight
• 9 = Nine
• 10 = Ten

I would like to reverse this integer sort of the TreeMap, So the highest integer will be at the front and the lowest and the end, How can I accomplish this? Thanks in advance.

Answer 1

TreeMap's constructor can take Comparator you can pass custom implementation

Change your Map declaration to pass reverse order comparator

Map<Integer, String> map = new TreeMap<Integer, String>(Collections.reverseOrder());

---

Also See

• Sorting a list of points with Java