Java TreeMap Comparator

Question

I need a comparator for a TreeMap. Should I write this anonymously in the constructor for my TreeMap? How else could I write my comparator. Currently, Java does not like my code (can I do this anonymously?):

SortedMap<String, Double> myMap =      new TreeMap<String, Double>(new Comparator<Entry<String, Double>>()     {         public int compare(Entry<String, Double> o1, Entry<String, Double> o2)         {             return o1.getValue().compareTo(o2.getValue());         }      }); 

1. Can I do the above anonymously?
2. How else could I do this?
3. I want to sort myMap by the Value not the Key

Answer 1

You can not sort TreeMap on values.

A Red-Black tree based NavigableMap implementation. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used You will need to provide comparator for Comparator<? super K> so your comparator should compare on keys.

To provide sort on values you will need SortedSet. Use

SortedSet<Map.Entry<String, Double>> sortedset = new TreeSet<Map.Entry<String, Double>>(             new Comparator<Map.Entry<String, Double>>() {                 @Override                 public int compare(Map.Entry<String, Double> e1,                         Map.Entry<String, Double> e2) {                     return e1.getValue().compareTo(e2.getValue());                 }             });    sortedset.addAll(myMap.entrySet()); 

To give you an example

    SortedMap<String, Double> myMap = new TreeMap<String, Double>();     myMap.put("a", 10.0);     myMap.put("b", 9.0);     myMap.put("c", 11.0);     myMap.put("d", 2.0);     sortedset.addAll(myMap.entrySet());     System.out.println(sortedset); 

Output:

  [d=2.0, b=9.0, a=10.0, c=11.0]