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Thread: Re: Error Message: Exception in thread "main" java.lang.NullPointerException etc.

  1. #1
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    Default Re: Error Message: Exception in thread "main" java.lang.NullPointerException etc.

    help me to solve this error: -

    import java.io.IOException;

    import java.net.InetAddress;

    import java.net.NetworkInterface;

    import java.net.URLConnection;
    import java.net.UnknownHostException;
    import java.net.*;


    public class IsReachable
    {


    public static void main(final String[] args) throws IOException
    {

    InetAddress host;
    try
    {


    for (int i = 1; i < 255; i++)
    {

    host = InetAddress.getByName("192.168.6." + i);

    NetworkInterface network = NetworkInterface.getByInetAddress(host);

    byte[] mac = new byte[100];
    mac=network.getHardwareAddress();


    StringBuilder sb = new StringBuilder();


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

    sb.append(String.format("%02X%s", mac[j], (j < mac.length - 1) ? "-" : ""));

    }


    if (host.isReachable(10000))
    {

    System.out.println("Connected " + host + " " + sb.toString());

    }
    else
    {

    System.out.println("Failed " + host);

    }

    }

    }
    catch (UnknownHostException e) {


    e.printStackTrace();


    }
    catch (SocketException e) {


    e.printStackTrace();

    }

    }

    }

    ____________Output______________


    C:\Program Files\Java\jdk1.6.0_05\bin>javac IsReachable.java

    C:\Program Files\Java\jdk1.6.0_05\bin>java IsReachable
    Exception in thread "main" java.lang.NullPointerException
    at IsReachable.main(IsReachable.java:32)

    thank u


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Error Message: Exception in thread "main" java.lang.NullPointerException etc.

    Exception in thread "main" java.lang.NullPointerException
    at IsReachable.main(IsReachable.java:32)
    Look at line 32 in the your source and see what variable is null. Then backtrack in the code to see why that variable does not have a valid value.
    If you can not tell which variable it is, add a println just before line 32 and print out the values of all the varibles on that line.

    Please edit your post and wrap your code with
    [code=java]
    <YOUR CODE HERE>
    [/code]
    to get highlighting and preserve formatting.
    If you don't understand my answer, don't ignore it, ask a question.

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