整数与IP地址转换

import java.util.*;
import java.io.*;

public class Main{
    public static void main(String[] args) throws Exception{
        Scanner sc = new Scanner(System.in);
        while(sc.hasNextLine()){
            String line1 = sc.nextLine();
            System.out.println(ip2num(line1));
            String line2 = sc.nextLine();
            long num  = Long.parseLong(line2);
            System.out.println(num2ip(num));
        }
    }

    public static Long ip2num(String ip){
        String[] segs = ip.split("\\.");

        long sum = 0L;
        long mul = 1L;
        for(int i = segs.length - 1; i >= 0; --i){
            sum += Long.parseLong(segs[i],10) * mul;
            mul *= 256;
        }
        return sum;
    }

    public static String num2ip(long num){
        String line = Long.toBinaryString(num);
        int len = line.length();
        int start = len - 1;
        StringBuilder sb = new StringBuilder();
        while((start >= 0) && (start - 7 >= 0)){
            sb.append(Integer.parseInt(line.substring(start - 7, start + 1), 2));
            sb.append(".");
            start -= 8;
        }
        if(start != -1){
            sb.append(Integer.parseInt(line.substring(0, start + 1), 2));
        }else{
            sb.deleteCharAt(sb.length() - 1);
        }
        String[] split = sb.toString().split("\\.");
        StringBuilder sb1 = new StringBuilder();
        for(int i = split.length - 1; i > 0; --i){
            sb1.append(split[i]);
            sb1.append(".");
        }
        sb1.append(split[0]);
        return sb1.toString();
    }
}