public void sort(String id1, SortDir dir1, String id2, SortDir dir2) {
        Collections.sort(rows, new RowComparator(id1, dir1, id2, dir2));
    }
@Test
    public void sortAlphaDescNumberDesc() {
        tm = unsortedDoubleTableModel();
        verifyRowOrder("unsorted", tm, UNSORTED_IDS);
        tm.sort(ALPHA, SortDir.DESC, NUMBER, SortDir.DESC);
        verifyRowOrder("adnd", tm, ROW_ORDER_AD_ND);
    }