Nice general way to sort nulls to the bottom, regardless?

Question

I\'m writing some custom Comparators, and I\'d like them to push null items to the bottom of the list, regardless of whether I\'m sorting ascending or descending. What\'s a

Answer 1

Following up on dfa's answer - what I want is that the nulls sort at the end without affecting the order of the non-nulls. So I want something more along the lines of this:

public class NullComparatorsTest extends TestCase {
    Comparator  forward = new Comparator() {
                                    public int compare(String a, String b) {
                                        return a.compareTo(b);
                                    }
                                };

    public void testIt() throws Exception {
        List strings = Arrays.asList(null, "aaa", null, "bbb", "ccc", null);
        Collections.sort(strings, NullComparators.atEnd(forward));
        assertEquals("[aaa, bbb, ccc, null, null, null]", strings.toString());
        Collections.sort(strings, NullComparators.atBeginning(forward));
        assertEquals("[null, null, null, aaa, bbb, ccc]", strings.toString());
    }
}

public class NullComparators {
    public static  Comparator atEnd(final Comparator comparator) {
        return new Comparator() {
            public int compare(T a, T b) {
                if (a == null && b == null)
                    return 0;
                if (a == null)
                    return 1;
                if (b == null)
                    return -1;
                return comparator.compare(a, b);
            }
        };
    }

    public static  Comparator atBeginning(final Comparator comparator) {
        return new Comparator() {
            public int compare(T a, T b) {
                if (a == null && b == null)
                    return 0;
                if (a == null)
                    return -1;
                if (b == null)
                    return 1;
                return comparator.compare(a, b);
            }
        };
    }
}

Full credit to dfa, though - this is just a minor modification of his work.