Threads - General Questions

What does a daemon thread do when all user threads finish?

What is the output of the following program?

class Main {
    public static void main(String[] args) throws Exception {
        java.util.concurrent.atomic.AtomicInteger c = new java.util.concurrent.atomic.AtomicInteger();
        Thread[] ts = new Thread[4];
        for (int i = 0; i < 4; i++) { ts[i] = new Thread(() -> { for (int k = 0; k < 1000; k++) c.incrementAndGet(); }); ts[i].start(); }
        for (Thread t : ts) t.join();
        System.out.println(c.get());
    }
}

Which method of Thread is deprecated because it is unsafe?

What is the output of the following program?

public class Main {
    public static void main(String[] args) throws Exception {
        var pool = java.util.concurrent.Executors.newSingleThreadExecutor();
        var f = pool.submit(() -> 6 * 7);
        System.out.println(f.get());
        pool.shutdown();
    }
}

Which Thread method should you call to run its code on a new thread?