Daemon

Question

Hi,
I'm trying to write a simple application that does nothing more than write a file to disk with the date and time every second. (It's only a test application).
The important thing is that while it is not actually writing the file it should not take up any CPU time - and it should only take up CPU time at the moment it is actually writing the file.
Now, from what I understand about deamons, a daemon thread will terminate if no other non-daemon threads are running. Is that correct?
Now, my question is this... how do I therefore go about construcing the application? Does my main thread need to run as a daemon? But won't it exit as soon as the second thread sleeps? And how many threads do I actually need to have? Or to put it all another way, if I call the method Thread.sleep(1000) does it occupy CPU time during the sleep phase? (In which case, I could be content with running just a single thread?)
One final question - if I need to write the file at precisely regular intervals would I not be better off using TimerTask and scheduleAtFixedRate()?
I'm sure there are plenty of daemon experts who will be able to explain this to me. Thanks for your help.
Damian

Answer 1

I meant basically if you have this as the only thread inside a JVM, you wouldn't have to worry about a Writer:
public class Bar {
        public static void main(String[] argv) throws Throwable {
                while(true) {
                        Thread.sleep(1000);
                        System.out.println(
                                new java.util.Date().toString()
                } // while
        } // main
} // BarThen you could use the shell to redirect the output to your file. If you want it to be proper, use a Timer, and be able to process other things, then use something like this (whitespace removed for the forum):
import java.util.*;
import java.io.*;
public class Bar {
     public static int DELAY = 1000;
     private static Timer timer = new Timer(false);     // do NOT make daemon
     public static void main(String[] argv) throws Throwable {
          timer.scheduleAtFixedRate( new DateTask()
               , DELAY
               , DELAY
          // now go and do whatever other processing your heart desires
     } // main
} // Bar
class DateTask extends TimerTask() {
     private PrintWriter out;
     public DateTask(String fileName) throws IOException {
          out = new PrintWriter( new FileWriter(fileName)
               , true     // don't buffer
     public void run() {
          try {
               out.println(
                    new java.util.Date().toString();
                    // or whatever your date format is
          } catch(IOException ioe) {
               ioe.printStackTrace();
          } // try catch
     } // run
} // DateTask