Getting ip address and putting it to socket -java

Question

InetAddress ipAddr;

What i'm trying to do here is i need to get ip address and then put it in socket

 public class L implements ActionListener{
  public void actionPerformed(final ActionEvent e){
      try {   
            s = new Socket(ipAddr.getHostAddress(), 6111);

            DataOutputStream dout = new DataOutputStream(s.getOutputStream());
            dout.writeUTF("L");
            dout.writeUTF(" ");
      } catch (IOException ex) {
         ex.printStackTrace();  
      }

  }
}

I'm having this error msg

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

Answer 1

You're getting this error because you're trying to call method on a null reference. You need to initialise ipAddr before using it to call methods which is described later in this answer.

s = new Socket(ipAddr.getHostAddress(), 6111);   // your code doesn't initialise ipAddr.

Currently, it is unclear from your question which IPAddress you want. So, I'm assuming you're looking for your system's loopback address (default). There are several options to initialise InetAddress as shown below:

    String url = "localhost";
    byte addr[] = {127, 0, 0, 1};  // loopback address
    InetAddress ip1 =  InetAddress.getByName(url);
    InetAddress ip2 =  InetAddress.getByAddress(addr);
    InetAddress ip3 =  InetAddress.getLocalHost();
    // proceed with your sample code by using any of these InetAddress references