Java 套接字上的空指针异常

在下面的代码中，我得到一个空指针异常（在标记行）。第一个方法（join）调用thread-joinThread来运行与主机过程的连接

    public void join () {           


                try {
                    socket = new Socket (address, 3150); //address received elsewhere
                    BufferedReader in = new BufferedReader (new InputStreamReader (socket.getInputStream ()));
                    PrintWriter out = new PrintWriter (socket.getOutputStream (), true);
                    joinThread jointhread = new joinThread (this);
                    out.write (user.getText ());
                    jointhread.start ();

                } catch (IOException e) {
                }
            });



    public class joinThread extends Thread  {
        MainScreenController controller;    
    public joinThread (MainScreenController controller) {
        this.controller = controller;
    }

    @Override
    public void run () {
        Socket socket = null;
        FXMLLoader fxmlLoader = new FXMLLoader ();
        String inRead =null ;
        try {
////////////////////////////////NPE    
            while (inRead==null) inRead = controller.in.readLine (); // Elsewhere a String will be sent 
    //to thissocket   
////////////////////////////////NPE

        } catch (IOException e) {
            e.printStackTrace ();
        }

TIA

---

已解决，在主类中未初始化（仅在联接方法中）