1. 题目

读题

HJ33 整数与IP地址间的转换 

考查点

2. 解法

思路

 二进制与十进制的互转

可参照   Java中十进制二进制相互转换的方法

代码逻辑

具体实现

public class IP2Num {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            System.out.println(convertIp10(sc.nextLine()));
            System.out.println(convertIp(sc.nextLine()));
        }
    }


    public static long convertIp10(String ip) {
        String[] ips = ip.split("\\.");
        StringBuffer sb = new StringBuffer();
        for (String cur : ips) {
            sb.append(binStr(cur));
        }
        return Long.parseLong(sb.toString(), 2);

    }

    private static String binStr(String s) {
        StringBuffer sb = new StringBuffer();
        int num = Integer.parseInt(s);
        int k = 1 << 7;
        for (int i = 0; i < 8; i++) {
            int flag = (num & k) == 0 ? 0 : 1;
            sb.append(flag);
            num = num << 1;
        }

        return sb.toString();
    }

    public static String convertIp(String ip10) {
        StringBuffer sb = new StringBuffer();
        String ip2 = Long.toBinaryString(Long.parseLong(ip10));
        String as = "";
        for (int i = 0; i < 32 - ip2.length(); i++) {
            as = as + "0";
        }
        ip2 = as + ip2;

        for (int i = 0; i < ip2.length(); i = i + 8) {
            sb.append(Long.parseLong(ip2.substring(i, i + 8), 2)).append(".");
        }
        return sb.deleteCharAt(sb.length() - 1).toString();
    }

}

3. 总结