### Question:
MapUtils { public static int getMaxKey(HashMap<Integer, String> map) { Set<Integer> keys = map.keySet(); Iterator<Integer> iterator = keys.iterator(); int max = 0; while (iterator.hasNext()) { max = Math.max(max, iterator.next()); } return max; }  static HashMap<String, String> tranToRatio(HashMap<Integer, Integer> table); static HashMap<Long, Integer> unionMaps(List<HashMap<Long, Integer>> table); static int getSum(HashMap<Long, Integer> table); static int[] getRealUses(HashMap<Long, Integer> table, int num); static String[] getRealRatio(HashMap<Long, Integer> table, int num); static int[] getRealCount(HashMap<Long, Integer> table, int num); static int getMaxKey(HashMap<Integer, String> map);  }### Answer:
@Test public void testGetMaxKey() { assertTrue(MapUtils.getMaxKey(map4) == 321); }