reorder an int as big as possible

 I found https://www.codewars.com/ and solving a algorithm question, reorder given number as big as possible, example given 123, ordered biggest version is 321, so we just need to order digits separately and concatenate them, I wrote 2 approaches

public void testStreamCode() {
    int num = 123;
    AtomicReference<String> str = new AtomicReference<>();
    String.valueOf(num).chars().boxed().sorted(Collections.reverseOrder()).forEach(c -> str.updateAndGet(v -> v + (c - 48)));
    int parseInt = Integer.parseInt(str.get().replaceAll("null", ""));
    assert parseInt == 321;
}

public void testArraysSortCode() {
    int num = 7657585;
    char[] c = String.valueOf(num).toCharArray();
    Arrays.sort(c);
    String s = "";
    for (int i = c.length - 1; i >= 0; i--)
        s += c[i];
    Integer integer = Integer.valueOf(s);
    assert integer == 8776555;
}

then CW gave another solution

public void cw() {
    int num = 7657585;
    int i1 = Integer.parseInt(String.valueOf(num)
            .chars()
            .mapToObj(i -> String.valueOf(Character.getNumericValue(i)))
            .sorted(Comparator.reverseOrder())
            .collect(Collectors.joining()));
    assert i1 == 8776555;
}

I know java stream api looks cool and I decided to benchmark this. here is the result

Benchmark                                Mode  Cnt  Score   Error  Units
DemoApplicationTests.cw                  avgt    2  0.808          us/op
DemoApplicationTests.testArraysSortCode  avgt    2  0.194          us/op
DemoApplicationTests.testStreamCode      avgt    2  0.884          us/op
 

fastest is using arrays.sort(0.194) second is CW and last one is "testStreamCode".