@Override
  public String toString() {
    return IntStream.range(0, size)
        .mapToObj(idx -> String.format("%02x", bytes[idx]))
        .collect(Collectors.joining(" "));
  }
@Test
  public void testToString() {
    checkToString(new byte[]{0,1,2,0x10}, "00 01 02 10");
    checkToString(new byte[]{-0x80, -0x7f, -0x1, -0x2, 1, 0}, 
                  "80 81 ff fe 01 00");
  }