Why this Java Thread program doesn't work as expected?

Question

Hello all:
I have a java code as follows:
My question is why tryThreadB which is set as deamon thread still run
after the main program return?
the output of this program looks like:
HopalongMarilyn HopalongMarilyn HopalongMarilyn HopalongMarilyn HopalongMarilyn Ending main()
HopalongMarilyn HopalongMarilyn HopalongMarilyn HopalongMarilyn HopalongMarilyn HopalongMarilyn
However, I think the correct output should be:
HopalongMarilyn HopalongMarilyn HopalongMarilyn HopalongMarilyn HopalongMarilyn Ending main()
Hopalong Hopalong Hopalong Hopalong Hopalong Hopalong Hopalong Hopalong
====================================
<pre>
import java.io.*;
public class TryThread extends Thread {
private String firstName;
public TryThread(String firstName) {
this.firstName = firstName;
public static void main(String[] args) {
TryThread tryThreadA = new TryThread("Hopalong");
TryThread tryThreadB = new TryThread("Marilyn ");
// user thread
tryThreadA.setDaemon(false);
// daemon thread
tryThreadB.setDaemon(true);
tryThreadA.start();
tryThreadB.start();
try {
sleep(5000);
catch (InterruptedException ex) {
System.out.println("Ending main()");
return;
public void run() {
try {
while(true) {
System.out.print(firstName);
sleep(1000);
catch (InterruptedException ex) {
System.out.println(ex);
</pre>
====================================
thank you very much

Answer 1

Hi,
From the Thread documentation:
When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls
the method named main of some designated class). The Java Virtual Machine continues to execute
threads until either of the following occurs:
    * The exit method of class Runtime has been called and the security manager has permitted the exit
operation to take place.
    * All threads that are not daemon threads have died, either by returning from the call to the run method
or by throwing an exception that propagates beyond the run method.A daemon thread will not stop after the main method returns. It will stop when there are only daemon threads executing.
So, in your case, thread B will continue to execute as long as thread A (or any other non-daemon thread) is alive.
/Kaj