请高手帮我完善

[无聊司马]

实现两个数字字符串相加的的算法 要求 ：
1>当两个数字字符串中的数字都为正数时代码我已给出
2>当两个数字字符串中的数字为一正一负时，请完善一下 代码就接下面写出就行了
3>当输入的异常时报错并输出错误信息
代码如下：

import java.util.Scanner;

public class ab {
	public static void main(String args[]) throws Exception {

		Scanner sc = new Scanner(System.in);
		String str1 = sc.next();
		String str2 = sc.next();
		String str3 = "";
		
		if (str1.length() > 1024 || str2.length() > 1024) {
			throw new Exception("err:输入数据长度超出范围！");
		}
		System.out.println(case1(str1,str2));

	}

	/*
	 * 当两个数都为正数
	 */
	public static String case1(String first, String second) throws Exception {
		String str3 = "";
		String ftemp = "";
		String stemp = "";
		String rtemp = "";
		int flag = 0;
		for (int i = 0; i < (first.length() > second.length() ? first.length()
				: second.length()); i++) {
			if (i < first.length()) {
				ftemp = first.substring(first.length() - 1 - i, first.length()
						- i);
			} else {
				ftemp = "0";
			}
			if (i < second.length()) {
				stemp = second.substring(second.length() - 1 - i, second
						.length()
						- i);
			} else {
				stemp = "0";
			}
			try {
				rtemp = ""
						+ (Integer.parseInt(ftemp) + Integer.parseInt(stemp) + flag);
				flag = 0;
				if (Integer.parseInt(rtemp) >= 10) { // 进位
					rtemp = "" + (Integer.parseInt(rtemp) - 10);
					flag = 1;
				}
				str3 = rtemp + str3;
			} catch (Exception e) {
				throw new Exception("err:输入格式错误");
			}
		}
		return str3;
	}
当两数为一正一负时  高手接：嘎嘎
}

[飞跃颠峰]

import java.util.Scanner;

public class ab {
    public static void main(String args[]) throws Exception {

        Scanner sc = new Scanner(System.in);
        String str1 = sc.next();
        String str2 = sc.next();
        String str3 = "";
        
        if (str1.length() > 1024 || str2.length() > 1024) {
            throw new Exception("err:输入数据长度超出范围！");
        }

        // 自动根据正负情况调用case1或case2
        if (!str1.startsWith("-") && !str2.startsWith("-"))
            System.out.println(case1(str1,str2));
        else if (str1.startsWith("-") && str2.startsWith("-"))
        	System.out.println("-" + case1(str1.substring(1),str2.substring(1)));
        else
        	System.out.println(case2(str1,str2));

    }

    /*
     * 当两个数都为正数
     */
    public static String case1(String first, String second) throws Exception {
        String str3 = "";
        String ftemp = "";
        String stemp = "";
        String rtemp = "";
        int flag = 0;
        for (int i = 0; i < (first.length() > second.length() ? first.length()
                : second.length()); i++) {
            if (i < first.length()) {
                ftemp = first.substring(first.length() - 1 - i, first.length()
                        - i);
            } else {
                ftemp = "0";
            }
            if (i < second.length()) {
                stemp = second.substring(second.length() - 1 - i, second
                        .length()
                        - i);
            } else {
                stemp = "0";
            }
            try {
                rtemp = ""
                        + (Integer.parseInt(ftemp) + Integer.parseInt(stemp) + flag);
                flag = 0;
                if (Integer.parseInt(rtemp) >= 10) { // 进位
                    rtemp = "" + (Integer.parseInt(rtemp) - 10);
                    flag = 1;
                }
                str3 = rtemp + str3;
            } catch (Exception e) {
                throw new Exception("err:输入格式错误");
            }
        }
        return str3;
    }

    //当两数为一正一负时
    public static String case2(String first, String second) throws Exception {
    	String str3="",big,small;
    	int flag=0,u,d;
    	boolean isnegative = false;
    	try {
			String positive = (first.startsWith("-")?second:first).replaceAll("^0*(\\d+)$", "$1");
			String negative = (first.startsWith("-")?first.substring(1):second.substring(1)).replaceAll("^0*(\\d+)$", "$1");
			if (positive.length()>negative.length() || positive.length()==negative.length() && positive.compareTo(negative)>=0) {
				big=positive;
				small=negative;
			} else {
				big=negative;
				small=positive;
				isnegative = true;
			}
			for (int i=1; i<=big.length(); i++) { // 按位计算循环开始
				u = Integer.parseInt(big.substring(big.length()-i,big.length()-i+1)) - flag;
				d = i>small.length()?0:Integer.parseInt(small.substring(small.length()-i,small.length()-i+1));
				if (u>=d) {
					str3 = (u-d) + str3;
					flag = 0;
				} else {
					str3 = (10+u-d) + str3;
					flag = 1;
				}
			}
			str3 = str3.replaceAll("^0*(\\d+)$", "$1"); //如果以0开始，去掉前面多余的0
		} catch (Exception e) {
            throw new Exception("err:输入格式错误");
		}
    	return isnegative?"-"+str3:str3;
    }
}

[qybao]

for example

import java.util.*;
public class Test {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        System.out.print("请输入第一个数：");
        String str1 = sc.nextLine();
        System.out.print("请输入第二个数：");
        String str2 = sc.nextLine();
        
        if (str1.length() > 1024 || str2.length() > 1024) {
            throw new Exception("err:输入数据长度超出范围！");
        }
        if ((! str1.matches("[-]?\\d+")) || (! str2.matches("[-]?\\d+"))) {
            throw new Exception("err:输入非法数据！");
        }
        if (str1.startsWith("-") && str2.startsWith("-")) {
            System.out.println("-" + sum(str1.substring(1), str2.substring(1)));
        } else if (str1.startsWith("-")) {
            System.out.println(sub(str2, str1.substring(1)));
        } else if (str2.startsWith("-")) {
            System.out.println(sub(str1, str2.substring(1)));
        } else {
            System.out.println(sum(str1,str2));
        }
    }

    public static String sum(String s1, String s2) {
        s1 = s1.replaceAll("^0*", "");
        s2 = s2.replaceAll("^0*", "");
        if (s1.length()==0 && s2.length()==0) {return "0";}
        else if (s1.length()==0) {return s2;}
        else if (s2.length()==0) {return s1;}

        char[] c1 = s1.toCharArray();
        char[] c2 = s2.toCharArray();
        int[] result = new int[c1.length<c2.length ? c2.length : c1.length];
        for (int i=0; i<result.length; i++) {result[i]=0;}
        StringBuilder sb = new StringBuilder();
        for (int i=result.length-1,j=c1.length-1,k=c2.length-1; i>=0; i--,j--,k--) {
            if (j>=0) {result[i] += (c1[j]-'0');}
            if (k>=0) {result[i] += (c2[k]-'0');}
            if (i>0 && result[i]>9) {
                result[i] = result[i]%10;
                result[i-1]++;
            }
            sb.insert(0, result[i]);
        }
        while (sb.length() > 0 && sb.charAt(0) == '0') {
            sb.delete(0, 1);
        }
        
        return sb.toString();
    }

    public static String sub(String s1, String s2) {
        s1 = s1.replaceAll("^0*", "");
        s2 = s2.replaceAll("^0*", "");
        if (s1.length()==0 && s2.length()==0) {return "0";}
        else if (s1.length()==0) {return "-" + s2;}
        else if (s2.length()==0) {return s1;}

        char[] c1 = s1.toCharArray();
        char[] c2 = s2.toCharArray();
        boolean flg = c1.length >= c2.length;
        if (c1.length == c2.length) {
            for (int i=0; i<c1.length; i++) {
                if (c1[i] < c2[i]) {
                    flg = false;
                    break;
                }
            }
        }
        if (!flg) {
            char[] tmp = c1;
            c1 = c2;
            c2 = tmp;
        }

        int[] result = new int[c1.length<c2.length ? c2.length : c1.length];
        for (int i=0; i<result.length; i++) {result[i]=0;}
        StringBuilder sb = new StringBuilder();
        for (int i=result.length-1,j=c1.length-1,k=c2.length-1; i>=0; i--,j--,k--) {
            if (j>=0) {result[i] += (c1[j]-'0');}
            if (k>=0) {result[i] -= (c2[k]-'0');}
            if (i>0 && result[i]<0) {
                result[i] += 10;
                result[i-1]--;
            }
            sb.append(result[i]);
        }
        for (int i=sb.length()-1; i>0; i--) {
            if (sb.charAt(i) == '0') {sb.delete(i, i+1);}
            else {break;}
        }
        
        if (!flg) {sb.append('-');}
        return sb.reverse().toString();
    }
}

[无聊司马]

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