java效率取随机不重复数

 //效率取随机不重复数
    public int[] takeRandom(int num) {
        Random rd = new Random();
        int[] rds = new int[num];//随机数数组
        List list = new ArrayList();//存放有序数字集合
        int index = 0;//随机索引
        for (int i = 0; i < num; i++) {
            list.add(i);
        }
        for (int i = 0; i < num; i++) {
            index = rd.nextInt(num - i);
            rds[i] = (Integer) list.get(index);
            list.remove(index);
        }
        return rds;
    }