code: private static boolean equivalent(char[] a, char[] b) {
          checkArgNotNull(a, "a");
          checkArgNotNull(b, "b");
          if (a == b) return true;
          int length = a.length;
          if (b.length != length) return false;
  
          outer:
          for (int i = 0; i < length; i++) {
              char ac = a[i];
              for (int j = 0; j < length; j++) {
                  if (ac == b[j]) continue outer;
              }
              return false;
          }
          return true;
      }
docs: order independent Array.equals()