Java Comparator implement to use Map as backend

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

public class Main {

  public static void main(String[] args) {

    HashMap<String, Double> map = new HashMap<String, Double>();
    map.put("CSS", 9.0);
    map.put("HTML", 6.0);
    map.put("Java", 7.0);
    map.put("Javascript", 10.0);
    //from  w  w w. j  a v a  2  s .co  m
    ValueComparator bvc = new ValueComparator(map);
    TreeMap<String, Double> sorted_map = new TreeMap<String, Double>(bvc);

    System.out.println("unsorted map: " + map);

    sorted_map.putAll(map);

    System.out.println("results: " + sorted_map);
  }
}

class ValueComparator implements Comparator<String> {

  Map<String, Double> base;

  public ValueComparator(Map<String, Double> base) {
    this.base = base;
  }

  public int compare(String a, String b) {
    if (base.get(a) >= base.get(b)) {
      return -1;
    } else {
      return 1;
    }
  }
}