Java Programming

i know that map generally is not intended for sorting by values, but i do want to get a key ordering by its values in desc order since all data is stored into map previously

and here is the code i tried to may it work, it works but i guess the cost time will be a map.keyset.size() * map.values.size() double squared

Map a = new HashMap();
a.put("1", new BigDecimal("1.2"));
a.put("2", new BigDecimal("1.3"));
a.put("3", new BigDecimal("1.1"));
a.put("4", new BigDecimal("1.0"));
a.put("5", new BigDecimal("1.6"));
a.put("6", new BigDecimal("1.0"));
List values = new ArrayList(a.values());
Collections.sort(values);
BigDecimal bd = null;
Set entry = a.entrySet();
List rsList = new ArrayList();
for(Iterator it = values.iterator(); it.hasNext();)
{
bd = (BigDecimal) it.next();
for(Iterator ij = entry.iterator(); ij.hasNext();)
{
Map.Entry et = (Map.Entry) ij.next();
if(et.getValue().toString().equals(bd.toString()))
{
System.out.println("gotit" + et.getKey());
rsList.add(et.getKey());
ij.remove();
}
}
}

is there any better way to perform this operation or i really should not use this data structure?