Sorting maps in Java based on it’s values

public class MapValueSort {

/** inner class to do soring of the map **/
private static class ValueComparer implements Comparator {
private Map  _data = null;
public ValueComparer (Map data){
super();
_data = data;
}

    public int compare(Object o1, Object o2) {
     String e1 = (String) _data.get(o1);
        String e2 = (String) _data.get(o2);
        return e1.compareTo(e2);
    }
}

public static void main(String[] args){

Map unsortedData = new HashMap();
unsortedData.put("2", "DEF");
unsortedData.put("1", "ABC");
unsortedData.put("4", "ZXY");
unsortedData.put("3", "BCD");

SortedMap sortedData = new TreeMap(new MapValueSort.ValueComparer(unsortedData));

printMap(unsortedData);

sortedData.putAll(unsortedData);
System.out.println();
printMap(sortedData);
}

private static void printMap(Map data) {
for (Iterator iter = data.keySet().iterator(); iter.hasNext();) {
String key = (String) iter.next();
System.out.println("Value/key:"+data.get(key)+"/"+key);
}
}

}

This should output something of the lines of:

Value/key:BCD/3
Value/key:DEF/2
Value/key:ZXY/4
Value/key:ABC/1

Value/key:ABC/1
Value/key:BCD/3
Value/key:DEF/2
Value/key:ZXY/4

Where the bottom last four lines obviously is sorted on the map’s values and not it’s keys.

Ref: http://paaloliver.wordpress.com/2006/01/24/sorting-maps-in-java/ by paaloliver