1 ip地址的格式：...坦弟，并且值不能超過255护锤，使用正則表達式

String pattern = "^(\\d|[1-9]\\d|1\\d{2}|2[0-4]\\d|25[0-5])(\\.(\\d|[1-9]\\d|1\\d{2}|2[0-4]\\d|25[0-5])){3}$";

2 掩碼除了要滿足ip地址的格式外，轉(zhuǎn)化為2進制后酿傍，0的后面不能有1

    public static boolean maskCheck(String str) {
        if (str != null && !str.isEmpty()) {
            String s[] = str.split("[.]");
            String binary = "";
            for (int i = 0; i < s.length; ++i) {
                binary = binary + getBinary(s[i]);
            }
            if (binary.contains("01"))
                return false;
            else return true;
        }
        return false;
    }

3 判斷兩個ip地址是否屬于同一網(wǎng)絡，比較子網(wǎng)掩碼為1的前幾位是否相同

public class Test {
    public static int checkNetSegment(String mask, String ip1, String ip2) {
        //驗證ip地址是否合法
        if ((ipCheck(mask) && maskCheck(mask)) == false || ipCheck(ip1) == false || ipCheck(ip2) == false)
            return 1;
        //求出網(wǎng)絡位
        String net[] = mask.split("[.]");
        int len = getlen(net[0]) + getlen(net[1]) + getlen(net[2]) + getlen(net[3]);
        //獲取ip的二進制
        String ip1s[] = ip1.split("[.]");
        String Ip1 = "";
        String Ip2 = "";
        String ip2s[] = ip2.split("[.]");

        int i = (len % 8 == 0 ? len / 8 : len / 8 + 1);
        for (int j = 0; j < i; ++j) {
            Ip1 = Ip1 + getBinary(ip1s[j]);
            Ip2 = Ip2 + getBinary(ip2s[j]);
        }
        if (len % 8 != 0) {
            return Ip1.substring(0, len).equals(Ip2.substring(0, len)) ? 0 : 2;
        } else
            return Ip1.equals(Ip2) ? 0 : 2;
    }

    public static int getlen(String s) {
        int n = Integer.parseInt(s);
        int m = 0;
        if (n == 0) {
            return 0;
        } else {
            while (n / 2 != 0) {
                if (n % 2 != 0) {
                    ++m;
                }
                n = n / 2;
            }
            return m + 1;
        }
    }

    public static String getBinary(String s) {
        String b[] = {"0", "00", "000", "0000", "00000", "000000", "0000000", ""};
        int n = Integer.parseInt(s);
        String m = "";
        if (n == 0)
            return "00000000";
        while (n / 2 != 0) {
            m = n % 2 + m;
            n = n / 2;
        }
        return (m.length() < 7 ? b[6 - m.length()] : "") + "1" + m;
    }

    public static boolean ipCheck(String str) {
        if (str != null && !str.isEmpty()) {
            String pattern = "^(\\d|[1-9]\\d|1\\d{2}|2[0-4]\\d|25[0-5])(\\.(\\d|[1-9]\\d|1\\d{2}|2[0-4]\\d|25[0-5])){3}$";
            if (str.matches(pattern))
                return true;
            return false;

        }
        return false;
    }

    public static boolean maskCheck(String str) {
        if (str != null && !str.isEmpty()) {
            String s[] = str.split("[.]");
            String binary = "";
            for (int i = 0; i < s.length; ++i) {
                binary = binary + getBinary(s[i]);
            }
            if (binary.contains("01"))
                return false;
            else return true;
        }
        return false;
    }

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        while (input.hasNext()) {
            String mask = input.next();
            String ip1 = input.next();
            String ip2 = input.next();
            System.out.println(checkNetSegment(mask,ip1,ip2));

        }
    }
}

• 輸出
  1：不滿足格式
  2：不在同一個子網(wǎng)
  0: 在同一個子網(wǎng)