How to stop a thread?

In general, you don’t forcibly stop threads because it’s dangerous. You set a flag that tells the thread in question to exit from it’s thread loop under controlled circumstances.

Your thread loop looks something along these lines:

void run() {
  while (shouldContinue) {
    doThreadWorkUnit();
  }
}

And somewhere else you set the shouldContinue variable and wait for the thread to finish:

...
thread.shouldContinue = false;
thread.join();
...

(All this is likely not correct Java, since I don’t do Java. View it as pseudo code and modify for your actual language/thread library/etc.)