t.java

import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;
import java.util.TreeSet;

public class t {

  static public void main(String[] args) {
    HashMap<String, Integer> hm = new HashMap<String, Integer>();
    hm.put("answer", 42);
    hm.put("none", 0);
    hm.put("pastis", 51);
    hm.put("vodka", 40);

    TreeSet<Map.Entry<String, Integer>> kvs = new TreeSet<Map.Entry<String, Integer>>(
        new Comparator() {
          public int compare(Object a, Object b) {
            Integer diff = (((Map.Entry<String, Integer>) b).getValue()
                            - ((Map.Entry<String, Integer>) a).getValue());
            return diff.intValue();
          }
        });

    kvs.addAll(hm.entrySet());
    if (kvs.size() != hm.size())
      throw new RuntimeException(String.format("OMG %d != %d", kvs.size(), hm.size()));

    for (Map.Entry<String, Integer> kv : kvs) {
      System.out.println("key="+kv.getKey()+" value="+kv.getValue());
    }
  }

}

/*
$ javac -Xlint t.java && java t
t.java:132: warning: [unchecked] unchecked cast
found   : java.lang.Object
required: java.util.Map.Entry<java.lang.String,java.lang.Integer>
            Integer diff = (((Map.Entry<String, Integer>) b).getValue()
                                                          ^
t.java:133: warning: [unchecked] unchecked cast
found   : java.lang.Object
required: java.util.Map.Entry<java.lang.String,java.lang.Integer>
                            - ((Map.Entry<String, Integer>) a).getValue());
                                                            ^
t.java:130: warning: [unchecked] unchecked conversion
found   : <anonymous java.util.Comparator>
required: java.util.Comparator<? super java.util.Map.Entry<java.lang.String,java.lang.Integer>>
        new Comparator() {
        ^
3 warnings
key=pastis value=51
key=answer value=42
key=vodka value=40
key=none value=0
*/