Question

public class thread extends Thread {

    static volatile boolean done = false;// volatile keyword is used            

@Override
public void run() {
    while (!done) {
        for (int i = 1; i < 10; i++) {

            try {
                thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(currentThread());
            System.out.println("1st thread>> " + i);
        }
    }
}

public static void main(String[] args) throws InterruptedException {

    Thread th = new Thread(new thread(),"mythread");
    th.start();
    for (int i = 1; i < 10; i++) {
        thread.sleep(400);
        System.out.println(currentThread());
        System.out.println("2nd thread>> " + i);
        if (i == 4) {
            done = true;// safe way to stop a thread
            break;
        }
    }

   }
  }

I am using volatile static variable here.Is it a safe way to stop a thread and also
when I print currentThread() method I get the output like Thread[mythread,5,main]
what does the 5 and main refer to??

Answer 1

It’s a safe way to stop a thread, but there is no reason for the variable to be static: you want to stop one thread, not all threads of the same class.
Moreover, there is a more standard and less fragile way to stop a thread: interrupting it.

public void run() {
    while (!Thread.currentThread().isInterrupted() {
        ...
    }
}

...

th.interrupt();

This has the additional advantage that a thread which is sleeping or waiting, or blocked in an interruptible IO method will be woken up with an InterruptedException. When such an exception happens, it means that the thread should stop running, so you shouldn’t swallow the exception as you did. Instead, you should return from the run method as fast as possible:

try {
    thread.sleep(200);
} 
catch (InterruptedException e) {
    return;
}