threads.md

When you start a thread your method run() is invoked. Until run() is in progress the thread is working. When run() is finished the thread stops and enters TERMINATED state. It's impossible to start the thread again after that.

Sometimes heavy work is done in threads that can take a lot of time. So what if application wants to stop those threads? Actually there is no way you can stop threads. You can only ask threads to stop and it's up to them to decide. Usually it happens like this:

public void run() {
    while(true) {
        if(Thread.currentThread().isInterrupted())
            break;
        //do work
    }
}

Note, that we check the flag of the current thread - did anyone ask us to stop (invoked thread.interrupt())? If so, we'll break the cycle. If no, we keep working. If we don't check the flag there is no way the thread can be stopped unless JVM is stopped.