隨機數唯一性算法？

public static void main(String[] args) {

List<Integer> list = new ArrayList<>();

HashSet<Integer> set = new HashSet<>();

for(int i=0; i<100000; i++) {

int hashCode = UUID.randomUUID().toString().replaceAll("-", "").hashCode();

hashCode = hashCode < 0 ? hashCode * -1 : hashCode;

list.add(hashCode);

}

set.addAll(list);

System.out.println(list.size());

System.out.println(set.size());

System.out.println(list.size()-set.size());

}