java : spawning new thread is causing original threrad to halt

Question

I have the following code in which I spawn a thread listen which is supposed to constantly listen to any incoming TCP messages, after this thread is run I want the main thread to be used for sending messages but as soon as I initiate listen.run() it seems that main thread does not run any further. I want it to continue to run the while loop but it never reaches it.

package tcpclient;

import java.io.*;
import java.net.*;
import java.net.UnknownHostException;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;

public class client {
//instance vars
static Socket cSocket =null;
static PrintWriter out = null;
static BufferedReader in = null;

//server info
static String serverName = null;
static int serverPort = 0;
static String userName=null;

//listening vars
static Thread listen;
static  String incoming=null;

/**
 * @param args the command line arguments
 */
public static void main(String[] args) throws IOException {
    try {
        System.out.println("\n\n\nTCP Chat Client\n\nEnter server name:");
        Scanner scan = new Scanner(System.in);

        //get server info from user
        serverName = scan.nextLine();

        System.out.println("\nEnter port number:");
        serverPort = Integer.parseInt(scan.nextLine());


        System.out.println("\nEnter your username:");
        userName = scan.nextLine();

        //make connection to server
        cSocket = new Socket(serverName, serverPort);
        out = new PrintWriter(cSocket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(cSocket.getInputStream()));

        //send username to server
        out.println(userName);

        //start listening
        listen = new Thread(){
            @Override
                public void run(){
                try {
                    incoming = in.readLine();
                    while (!(incoming.equals(null))) {
                        System.out.print(incoming);


incoming = in.readLine();

                    }
                } catch (IOException ex) {
                    Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
                }
            }

        };
        listen.run();
        String rcvrname="wefwef";
        String message=null;
        //start messaging
        while(!(rcvrname.equals("exit"))){
            System.out.println("Enter reciever name");
            out.println(scan.nextLine());
            System.out.println("Enter message");
            out.println(scan.nextLine());

        }
        out.close();
        in.close();
        cSocket.close();

    }

    catch (UnknownHostException ex) {
        System.err.println("\ncan't find that host\n");

    }

    catch (IOException ex) {
        Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
    }

   finally{
        in.close();
        out.close();
        cSocket.close();
   }


}

}

Answer 1

You want:

listen.start();

not

listen.run();

Also the preferred way of doing this since Java 5 is to use an ExecutorService:

Runnable listen = new Runnable() {
  public void run() { ... }
}
ExecutorService exec = Executors.newSingleThreadExecutor();
exec.submit(listen);

and when you want to stop it:

exec.shutdown();
exec.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);

or simply:

exec.shutdownNow();

Answer 2

Here is the problem:

listen.run();

You mustn't call run() itself! You should call start(), this spawns a thread, calling run() just call a function.