package demo;

import java.util.HashSet;

import java.util.Random;

public class RandomDemo {

    public static void main(String[] args) {

        HashSet<Integer> hashSet = new HashSet();

        randomSet(hashSet);

        System.out.println(hashSet);

    }

    private static void randomSet(HashSet<Integer> hashSet) {

        if (hashSet.size() == 10) { //如果hashSet等于10，不需要递归

            return;

        }

        Random random = new Random();

        for (int i = 0; i < 10 - hashSet.size(); i++) {

            hashSet.add(random.nextInt(20) + 1);

        }

        if (hashSet.size() < 10) {// 如果hashSet不足10个，递归

            randomSet(hashSet);

        }

    }

}