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;
     }