Java 两大数相乘

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());
}
}