# Daemon Thread Java Code Quiz

> In your Java applications, do you know if the main Thread is a daemon or not? And do you know what a daemon Thread is?

- URL: https://foojay.io/today/daemon-thread-java-code-quiz/
- Published: 2021-09-08
- Authors: Rafael del Nero
- Categories: Tutorials


When we are working with Threads, it's important to know when to use a daemon or a non-daemon Thread.

Do you know if the main Thread is a daemon or not? And do you know what a daemon Thread is?

That's what you will find out by trying out the following Java Challenge!

It's time to improve your Java skills with this Daemon Thread Challenge...

## Daemon Thread Challenge

What will happen when running the following main method?

```java
public class DaemonThreadChallenge implements Runnable {

        public static void main(String... doYourBest) {
            Thread thread = new Thread(new DaemonThreadChallenge());
            thread.setDaemon(true);
            thread.start();
        }

        @Override
        public void run() {
            for (;;) {
                System.out.println("For ever");
            }
        }
}
```

A) It will print "Forever" for an indeterminate time and the program will finish normally.  

B) It will throw StackOverflowError because of the infinite looping.  

C) It will print "Forever" infinitely.

**Explanation**:

The amount of time that `"Forever"` will be printed is indeterminate because it will depend on the time from the main thread execution.

There are two types of threads:

* **Non-daemon**: the main method is executed with a non-daemon thread behind the scenes and this thread will be executed until the end.
* **Daemon**: it will die if all non-daemon threads have finished. So in this quiz, if the main method is finished, the daemon thread we created will be finished as well because all daemon threads depend on a non-daemon thread to continue its execution.

Therefore, the final answer will be... what do you think?

That's it challenger, keep pushing your limits to be a better software developer!