如何将字符串转换为bigInteger并存储在哈希集？

import java.math.BigInteger;
import java.util.HashSet;

HashSet<BigInteger> hashSet = new HashSet<>();

String str = "123456789";

BigInteger bigInteger = new BigInteger(str);

hashSet.add(bigInteger);

import java.math.BigInteger;
import java.util.HashSet;

public class Main {
    public static void main(String[] args) {
        HashSet<BigInteger> hashSet = new HashSet<>();
        String str = "123456789";
        BigInteger bigInteger = new BigInteger(str);
        hashSet.add(bigInteger);
        
        System.out.println("哈希集合中的BigInteger对象：" + hashSet);
    }
}