code: private void ensurePowerOfTwo(String parameter, int number) {
          if (Integer.bitCount(number) > 1) {
              if (log.isLoggable(Level.WARNING)) {
                  log.warning("Parameter '" + parameter + "' should be power of two but was " + number);
              }
          }
      }
docs: all the capacities will be used to initialize HashMaps so they should be powers of two