public static synchronized long getRandomNonNegativeLong() {
    return sRandom.nextLong() & Long.MAX_VALUE;
  }
@Test
  public void getRandomNonNegativeLong() throws Exception {
    long first = IdUtils.getRandomNonNegativeLong();
    long second = IdUtils.getRandomNonNegativeLong();
    assertTrue(first >= 0);
    assertTrue(second >= 0);
    assertTrue(first != second);
  }