Control the activity flow in thread T1 using thread T2

Question

Hi, im asking this question because i have two threads, one running at background, one at foreground directly interacting with users. the two should also intereact with each other, and perform correct actions depending on the command/request received from the other. for instance,
Class BackgroundThread implements Runnable{
    private boolean _stop;
    public void run(){
        while(!shouldStop(){
            //do something
    public boolean shouldStop(){
        return _stop;
    public void signalStop(){
        _stop=false;
    public void signalContinue(){
        _stop=true;
Class ForegroundThread implements Runnable{
    BackgroundThread _bgThread;
    public ForegroundThread (BackgroundThread bgThread){
        _bgThread=bgThread;
    public void run(){
        // lines of code that catches user input from console
        case 'r'
            _bgThread.signalContinue();    //LINE A
            break;
        case 's'
            _bgThread.signalStop();   
            break;
public Class ClientMain(){
    public static void main(args[]){
        BackgroundThread bgT = new BackgroundThread();
        new Thread(bgT).start();
        new ForegroundThread (bgT).run;
    }these are just sample code, may have errors, but the logic i suppose is clear. basically users interact with foreground thread, and they can control the running of background thread by typing command, r and s. 's' signal stop, 'r' signal continue.
at present i managed to stop the background thread - strictly not stopping it, but stop goin into the 'while' loop - once user key in 's'; but then if i key in 'r', the program does nothing. while what i want the system to do is to resume the execution of 'while'. i tried to replace the line A to
_bgThread.signalContinue();
_bgThread.run();and it does re-run, but then i cannot control the thread no more. ie, it doesnt stop upon command 's' anymore.
how can i fix this please, any hints? thanks very much in advance!

Answer 1

when the background thread exits the while loop, the thread stops and exits.
try this, it works, but obviously will need to be customized for what you want to do. It should give you an idea though.
class BackgroundThread implements Runnable
    private boolean _stop;
    private boolean _wait = true;
    public void run(){
         while(_wait)
             while(!shouldStop()){
                  try{
                       Thread.sleep(1000);
                       System.out.println("Do Something");
                  catch(InterruptedException ie)
             try{
                  Thread.sleep(1000);
             catch(InterruptedException ie)
             System.out.println("Paused...");
    public boolean shouldStop(){
        return _stop;
    public void signalStop(){
        _stop=true;
    public void signalContinue(){
        _stop=false;
    public void signalPause()
         _stop = true;
    public void signalExit()
         _wait = false;
         _stop = true;
class ForegroundThread implements Runnable{
    BackgroundThread _bgThread;
    public ForegroundThread (BackgroundThread bgThread){
        _bgThread=bgThread;
    public void run(){
        // lines of code that catches user input from console
        Scanner scan = new Scanner(System.in);
        boolean exit = false;
         while(!exit)
             System.out.println("enter action");
             char resp = scan.next().charAt(0);
             switch(resp)
              case 'r':
                 _bgThread.signalContinue();    //LINE A
                 break;
             case 's':
                 _bgThread.signalPause();   
                 break;
             case 'e':
                  _bgThread.signalExit();
                  exit = true;
                  break;
public class ClientMain
    public static void main(String [] args )
        BackgroundThread bgT = new BackgroundThread();
        new Thread(bgT).start();
        new ForegroundThread(bgT).run();
}