两个超长数字字符串相加

需求两个很长的字符串数字相加，不使用第三方函数，手写算法，目前只写了不带小数点的相加，减法也没实现

---

public class AddLongStr {

private static String addNumStr(String str1,String str2) {

StringBuilder sumNum = new StringBuilder();

int len = str1.length();

int len1 = str1.length();

int len2 = str2.length();

String gaoW = "";

if (len1 > len2) {

len = str2.length();

gaoW = str1.substring(0, len1 - len);

}else {

len = str1.length();

gaoW = str2.substring(0, len2 - len);

}

System.out.println("len="+len);

int ten = 0;

for (int i = 1; i<=len; i++) {

int sum = Integer.parseInt(String.valueOf(str1.charAt(len1-i))) + Integer.parseInt(String.valueOf(str2.charAt(len2-i))) + ten;

ten = sum/10;

sumNum.insert(0, sum%10);

}

System.out.println("sumNum="+sumNum.toString());

StringBuilder gaoSumString =new StringBuilder();

if (null != gaoW && !gaoW.equals("")) {

System.out.println("gaoW="+gaoW);

int sl = gaoW.length();

int ten2 = 0;

for (int i = sl-1; i >=0; i--) {

int sum = 0;

if (i==sl-1) {

sum = (Integer.parseInt(String.valueOf(gaoW.charAt(i)))) + ten+ ten2;

}else {

sum = (Integer.parseInt(String.valueOf(gaoW.charAt(i)))) + ten2;

}

ten2 = sum/10;

gaoSumString.insert(0, sum%10);

}

if (ten2>0) {

gaoSumString.insert(0, ten2);

}

}

sumNum = gaoSumString.append(sumNum);

return sumNum.toString();

}

public static void main(String[] args) {

System.out.println(addNumStr("777","99933"));

}

}

有兴趣的可以一起检查错误和优化完善