java - 字符串乘法

Question

我正在尝试将两个字符串相乘，但我得到了错误的答案。任何帮助将不胜感激:

public class stringmultiplication {
    public static void main(String[] args) {
        String s1 = "10";
        String s2 = "20";
        int num = 0;
        for(int i = (s1.toCharArray().length); i > 0; i--)
            for(int j = (s2.toCharArray().length); j > 0; j--)
                num = (num * 10) + ((s1.toCharArray()[i - 1] - '0') * (s2.toCharArray()[j - 1] - '0'));
        System.out.println(num);
    }
}

Answer 1

public static void main(String[] args) {
        String number1 = "108";
        String number2 = "84";

        char[] n1 = number1.toCharArray();
        char[] n2 = number2.toCharArray();

        int result = 0;

        for (int i = 0; i < n1.length; i++) {
            for (int j = 0; j < n2.length; j++) {
                result += (n1[i] - '0') * (n2[j] - '0')
                        * (int) Math.pow(10, n1.length + n2.length - (i + j + 2));
            }
        }
        System.out.println(result);
    }

这应该是不使用整数的正确实现。