/** Create a map from Integers -5 to -1 to Strings "A"-"E". */
 private static ConcurrentNavigableMap dmap5() {
   ConcurrentSkipListMap map = new ConcurrentSkipListMap();
   assertTrue(map.isEmpty());
   map.put(m1, "A");
   map.put(m5, "E");
   map.put(m3, "C");
   map.put(m2, "B");
   map.put(m4, "D");
   assertFalse(map.isEmpty());
   assertEquals(5, map.size());
   return map.descendingMap();
 }
 private static ConcurrentNavigableMap dmap0() {
   ConcurrentSkipListMap map = new ConcurrentSkipListMap();
   assertTrue(map.isEmpty());
   return map;
 }
 /** Create a map from Integers 1-5 to Strings "A"-"E". */
 private static ConcurrentNavigableMap map5() {
   ConcurrentSkipListMap map = new ConcurrentSkipListMap();
   assertTrue(map.isEmpty());
   map.put(zero, "Z");
   map.put(one, "A");
   map.put(five, "E");
   map.put(three, "C");
   map.put(two, "B");
   map.put(four, "D");
   map.put(seven, "F");
   assertFalse(map.isEmpty());
   assertEquals(7, map.size());
   return map.subMap(one, true, seven, false);
 }