通过IP获取局域网内手机的NetworkInterface时总返回null
现在通过路由器已知手机的ip是192.168.1.100，用这个IP通过下面的代码获得的NetworkInterface总为null。

但是，局域网内运行此代码的台式机的IP为192.168.1.110，用这个IP通过下面的代码获得的NetworkInterface就正常，也能获得对应的MAC地址。请问这是怎么回事？

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

    {

        String ip123 = "192.168.1.";

        boolean found = false;

        

        for (int ip4 = 100; ip4 < 200; ++ip4)

        {

            String curIp = ip123 + ip4;

            NetworkInterface ni;

            

            try

            {

                InetAddress ia = InetAddress.getByName(curIp);

                ni = NetworkInterface.getByInetAddress(ia);

            }

            catch (Exception e)

            {

                System.out.println("IP地址：" + curIp + "非法。");

                continue;

            }



            if (null == ni)

            {

                continue;

            }

            else

            {

                String macStr = "";

                byte[] mac = ni.getHardwareAddress();

                for (int i = 0; i < mac.length; ++i)

                {

                    if (i != 0)

                    {

                        macStr += "-";

                    }

                    

                    //mac[i] & 0xFF 是为了把byte转化为正整数

                    String curMacSection = Integer.toHexString(mac[i] & 0xFF);

                    macStr += curMacSection; 

                }

                

                String targetMac = "5C-E8-EB-BA-F3-D8";

                if (0 == macStr.compareToIgnoreCase(targetMac))

                {

                    //在Windows资源管理器中打开ftp地址。

                    String cmd = "explorer ftp://" + curIp + ":2121";

                    Runtime.getRuntime().exec(cmd);

                    

                    found = true;

                    break;