如何获取BigInteger中的第n位数字？

import java.math.BigInteger;

public class BigIntegerExample {
    public static void main(String[] args) {
        BigInteger number = new BigInteger("12345678901234567890");
        int n = 5;

        String numberString = number.toString();
        int length = numberString.length();

        if (n >= 1 && n <= length) {
            char digitChar = numberString.charAt(length - n);
            int digit = Character.getNumericValue(digitChar);
            System.out.println("第" + n + "位数字为：" + digit);
        } else {
            System.out.println("第" + n + "位不存在");
        }
    }
}