Java 两大数相乘

两大数相乘（若是相加的话就更容易了）

public class Snippet {

    public static void main(String[] args) {
        // System.out.println("Hello world");

        //String str1 = "1234";
        //String str2 = "1234";
        //String str1 = "1076060999";
        //String str2 = "90188905567";
        String str1 = "15";
        String str2 = "15";


        System.out.println("乘数："+str1);
        System.out.println("乘数："+str2);
        bigNumberSimpleMulti(str1,str2);

    }
    public static void bigNumberSimpleMulti(String f, String s) {
            System.out.print("乘法：\n" + f + "*" + s + "=");
            // 获取首字符，判断是否是符号位
            char signA = f.charAt(0);
            char signB = s.charAt(0);
            char sign = '+';
            if (signA == '+' || signA == '-') {
                sign = signA;
                f = f.substring(1);
            }
            if (signB == '+' || signB == '-') {
                if (sign == signB) {
                    sign = '+';
                } else {
                    sign = '-';
                }
                s = s.substring(1);
            }
            // 将大数翻转并转换成字符数组
            char[] a = new StringBuffer(f).reverse().toString().toCharArray();
            char[] b = new StringBuffer(s).reverse().toString().toCharArray();
            int lenA = a.length;
            int lenB = b.length;
            // 计算最终的最大长度
            int len = lenA + lenB;
            int[] result = new int[len];
            // 计算结果集合
            for (int i = 0; i < a.length; i++) {
                for (int j = 0; j < b.length; j++) {
                    result[i + j] += (int) (a[i] - '0') * (int) (b[j] - '0');
                }
            }
            // 处理结果集合，如果是大于10的就向前一位进位，本身进行除10取余
            for (int i = 0; i < result.length; i++) {
                if (result[i] > 10) {
                    result[i + 1] += result[i] / 10;
                    result[i] %= 10;
                }
            }
            StringBuffer sb = new StringBuffer();
            // 该字段用于标识是否有前置0，如果是0就不需要打印或者存储下来
            boolean flag = true;
            for (int i = len - 1; i >= 0; i--) {
                if (result[i] == 0 && flag) {
                    continue;
                } else {
                    flag = false;
                }
                sb.append(result[i]);
            }
            if (!sb.toString().equals("")) {
                if (sign == '-') {
                    sb.insert(0, sign);
                }
            } else {
                sb.append(0);
            }
            // 返回最终结果
            System.out.println(sb.toString());
        }
}