大数字之和 Java实现

package Exercises;

import java.util.Arrays;
import java.util.Scanner;

/**
 * 大数字之和, 字符串-字符数组实现
 * 2020 07 12
 */
public class TheSumOfLargeNumbers {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s1 = in.nextLine();
        String s2 = in.nextLine();


        System.out.println(s1);
        System.out.println(s2);
        System.out.println(add(s1,s2));
    }

    public static String add(String s1, String s2){
        if (s1 == null||s2==null) {
            return "null";
        }

        char[] arr1=s1.length()>s2.length()?s1.toCharArray():s2.toCharArray();
        char[] arr2=s1.length()>s2.length()?s2.toCharArray():s1.toCharArray();
        int l=arr1.length+1;
        int[] sum=new int[l];
        StringBuilder result = new StringBuilder();
        char t;//将char类型的ascli码转为int只需要  -'0'
        for (int i = 0; i < arr1.length; i++) {
            sum[i]=arr1[arr1.length-1-i]-'0';
        }
        for (int i = 0; i < arr2.length; i++) {
            sum[i]+=arr2[arr2.length-1-i]-'0';
        }
        for (int i = 0; i < l; i++) {
            if (sum[i]>9) {
                sum[i]-=10;
                sum[i+1]++;
            }
        }
        boolean flag=false;
        for (int i = sum.length-1; i >=0; i--) {
            if (sum[i]!=0) {
                flag=true;
            }
            if(flag){
                result.append(sum[i]);
            }
        }
        return  result.toString();
    }
}