How do I run my client socket in seperate threads in Java?

Question

I am writing a program to control multiple Pc's over a network switch. I don't know enough about mulithreading to understand how the memory is handled, but how can I call infSockeThread.start(); and have connect to ip1, ip2, ip3..? When I issue my code as is it obviously just overwrites the memory in the InfoSocket class the second time I call it. Basically, I want to run the InfoSocket class as many times as their are PCs, each with their own unique connection to each PC.

For instance, I am calling this in my main class:

        String[] compTestArray = {"172.16.98.6", "172.16.98.3"};

        for(int i = 0; i < compTestArray.length; i++){

            InfoSocket infSocket = new InfoSocket(compTestArray[i]);
            Runnable infRunnable = infSocket;
            Thread infSockeThread = new Thread(infRunnable);

            infSockeThread.start();

        }

And then I have my socket class:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class InfoSocket implements Runnable {

    protected static Socket infoSocket;
    protected static PrintWriter out;
    protected static BufferedReader in;
    protected static String ip;

    public InfoSocket(String ipaddress){

        ip = ipaddress;

    }

    @Override
    public void run() {

        System.out.println("InfoSocket Thread Started");
        // TODO Auto-generated method stub
        String hostName = ip, fromServer = null;
        int portNumber = 6000;
        boolean socketConnected = false;

        while (!socketConnected) {

            try {

                Main.textArea.append("Attempting to connect to " + hostName
                        + "\n");
                Thread.sleep(5000);
                infoSocket = new Socket(hostName, portNumber);
                out = new PrintWriter(infoSocket.getOutputStream(), true);
                in = new BufferedReader(new InputStreamReader(
                        infoSocket.getInputStream()));

                System.out.println("Connected sent to server");

                // BREAK POINT
                fromServer = in.readLine();

                while (!fromServer.equals("connect")) {

                    Thread.sleep(1000);
                    System.out.print("Waiting for connection response from machine");

                }

                sendResponse(fromServer);

                // Break while loop because connection was successful
                socketConnected = true;

            } catch (Exception e) {
                e.printStackTrace();
                Main.textArea.append("Connection to " + hostName
                        + " failed, trying again\n");
            }
        }

        while (socketConnected) {

            System.out.println("Thread to send response sleeping");

            // Sleep for a second
            try {
                Thread.sleep(300);
                // Get info from server if available
                fromServer = in.readLine();
                System.out.println("From Server: " + fromServer + "\n");
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            // Send response back to server based off
            // of its input, only if the input is not equal to 'null'
            try {
                if (fromServer != null) {

                    System.out.println("Hit sendResponse");
                    sendResponse(fromServer);

                }

            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

    }

    public static String sendResponse(String action)
            throws InterruptedException, IOException {

        String str = " "; // Value to hold string to be returned

        System.out.println("\nInside sendResponse");
        System.out.println("Inside sendResponse & action is " + action + "\n");

        switch (action) {

        case "connect":
            System.out.println("Inside connect");
            out.println("success");
            break;
        case "ready":
            System.out.println("Inside ready");
            out.println("success");
            break;
        case "sync":
            System.out.println("Inside sync");
            Thread.sleep(10000);
            out.println("success");
            break;
        default:
            out.println(" ");

        }

        System.out.println("end of sendResponse");

        return str;

    }

}

Answer 1

The fields in InfoSocket shouldn't be static. That is why it overwrites the memory the second time you call it. If they were not static, each InfoSocket instance would have its own copy of those variables.

By the way, there is no need to write:

Runnable infRunnable = infSocket;

An InfoSocket is already Runnable. You can simply write:

Thread infSockeThread = new Thread(infSocket);