public int compareTo(Object o) {
        if (o instanceof Row) {
            Row r2 = (Row) o;
            int value = 0;
            if (useComparable != null) {
                for (int x = 0; x < useComparable.length; ++x) {
                    if (sortDirection[x] == Column.ASCENDING) {
                        value = 1;
                    } else { // Column.DESCENDING
                        value = -1;
                    }
                    if (useComparable[x]) {
                        if (ckey[x] == null) {
                            return -value;
                        } else if (r2.ckey[x] == null) {
                            return value;
                        } else if (ckey[x].compareTo(r2.ckey[x]) > 0) {
                            return value;
                        } else if (ckey[x].compareTo(r2.ckey[x]) < 0) {
                            return -value;
                        }
                    } else {
                        if (key[x] > r2.key[x]) {
                            return value;
                        } else if (key[x] < r2.key[x]) {
                            return -value;
                        }
                    }
                }
            } else {
                return 1;
            }
            // finally check version number
            if (versionNumber < r2.versionNumber) {
                return -1;
            } else if (versionNumber > r2.versionNumber) {
                return 1;
            }
        }
        return 0