How to stop threads in Java?

Question

I have made a java program with GUI and I want a stop button functionality in which when a user clicks on the stop button, the program must be stopped.

1. In m

Answer 1

Generally speaking, the way to do this is to have each of the other threads periodically check a flag. Often background threads loop, waiting for work - they just have to check the flag each time they go round a loop. If they're using Object.wait() or something similar to be told that there's more work, the same notification should be used to indicate that the thread should stop too. (Don't just spin until you're stopped - that will suck CPU. Don't just use sleep - that will delay termination.)

That allows all threads to terminate cleanly, releasing resources appropriately. Other options such as interrupt() and the deprecated destroy() method are much harder to control properly, IMO. (Interrupting a thread is better than hard-aborting it, but it has its own set of problems - such as the interruption is only processed at certain points anyway.)

EDIT: In code, it would look something like:

// Client code
for (Task task : tasks) {
  task.stop();
}

// Threading code
public abstract class Task implements Runnable {

  private volatile boolean stopped = false;

  public void stop() {
    stopped = true;
  }

  protected boolean shouldStop() {
    return stopped;
  }

  public abstract void run();
}

Your tasks would then subclass Task. You would need to make it slightly more complicated if you wanted the stop() method to also notify a monitor, but that's the basic idea.

Sample task:

public class SomeTask extends Task {
  public void run() {
    while (!shouldStop()) {
      // Do work
    }
  }
}

Answer 2

I don't think the answer solve the issue. here the code:

public class SomeTask extends Task {
   public void run() {
      while (!shouldStop()) {
        // Do work
      }
    }
  }

But how to handle if the "Do work" hang and does not return? In this case, the while cannot check the flag. The Thread still cannot stop.

The possible solution to this might be using Process.

Answer 3

Have a controller object which has a flag whether the threads should stop or not and each thread checks the controller periodically and exits if stop button is clicked (for example if you are transferring a file, then after each block is received/sent, check if stop is clicked).