for (int i = 0; i < ns.length - 1; i++) {
    for (int j = 0; j < ns.length - i - 1; j++) {
        if (ns[j] < ns[j+1]) {
            // 交换ns[j]和ns[j+1]:            int tmp = ns[j];            ns[j] = ns[j+1];            ns[j+1] = tmp;        }
    }
}