将NetworkInterface对象转换为字节数组的错误

Question

我的代码每次到达创建字节数组时都会挂起，我似乎无法弄清楚原因。请原谅我一直在尝试的一切评论。我得到一个空指针异常。到目前为止，这是我的方法。

@SuppressWarnings("static-access")
public static void NetworkScan() throws IOException{

    InetAddress ip;

    ip = InetAddress.getLocalHost();
    System.out.println("Current IP address : " + ip.getHostAddress());

    String ipstring =ip.getHostAddress();
    ipstring = ipstring.substring(0, 10);

    //StringBuilder ipstring2 = new StringBuilder(ipstring.substring(0, 12));
    //System.out.println(ipstring);

    for(int i=100; i<=200; i++){// ip range for routers is 100-200
        String ipstring2 = ipstring + i;

        //System.out.println(ipstring2);

        ip = ip.getByName(ipstring2);
        //System.out.println(ip.getHostAddress());
        if(ip.isReachable(5000)){
            try {

                //ip = InetAddress.getLocalHost();
                //System.out.println("Current IP address : " + ip.getHostAddress());

                //NetworkInterface network = NetworkInterface.getByInetAddress(ip);
                NetworkInterface network = NetworkInterface.getByName(ip.getHostAddress());
                byte[] mac = network.getHardwareAddress();

                System.out.print("Current MAC address : ");

                StringBuilder sb = new StringBuilder();
                for (int j = 0; j < mac.length; j++) {
                    sb.append(String.format("%02X%s", mac[j], (j < mac.length - 1) ? "-" : ""));        
                }
                System.out.println(sb.toString());
                writeFile(sb);

            }catch (SocketException e){

                e.printStackTrace();

            }//end try catch
        }else{//end if
            System.out.println(ip.getHostAddress() + " IP is not reachable");
        }
    }

}//end NetworkScan

我已经查看了与我类似的其他代码，他们似乎没有这个问题，但这可能是我一直在寻找的东西。