Comparator 從小到大排序（即：o1，o2）Comparator：

class A implements Comparator<A>{
    public int n;
    @Override
        public int compare(A o1, A o2) {
        // TODO Auto-generated method stub
        if (o1.n > o2.n) {
            return 1;
        } else if(o1.n == o2.n) {
            return 0;
        } else {
            return -1;
        }
    }
}