How to iterate hashmap with highest String key value

HashMap<string, string=""> mapp=new HashMap<string, string="">(); mapp.put("ab","blue"); mapp.put("abc","black"); mapp.put("abcef","black"); mapp.put("abcd","pink"); for (Iterator it = alltyp.iterator(); it.hasNext();) { String finalstring = (String) it.next();

                          Iterator it1=mapp.entrySet().iterator();
                          while(it1.hasNext())
                          {
                              Map.Entry pairs = (Map.Entry) it1.next();
                              String key_ = (String) pairs.getKey();
                              String value_ = (String) pairs.getValue();
                              finalstring = finalstring.replaceAll(key_, value_);

                          }

                      }

I want to iterate with max key value means key value "abcdef" should iterate first then "abcd" then "abc". so that my replaceall function should replace highest value first.