Worker threads in Swing

[angstrem]

I'm curious, where and when do all the Swing's worker threads spawn?
The question raised, when I tried to invoke SwingWorker's execute() method from the main() method of a console application (just for the test purposes) and got no result. I had to use ExecutorService.submit(SwingWorker) method in order to make it execute.

[Norm]

Can you make a small program that compiles, executes and shows what happened?

[angstrem]

Yes, here's the program, who does not run:

import javax.swing.SwingWorker;
 
public class Polygon {
 
    public static void main(String[] args) {
        SwingWorker<Void, Void> w = new SwingWorker<Void, Void>() {
 
            @Override
            protected Void doInBackground() throws Exception {
                System.out.println("I'm started!");
                return null;
            }
        };
        w.execute();
    }
}

Here's the program, who runs.

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import javax.swing.SwingWorker;
 
public class Polygon {
 
    public static void main(String[] args) {
        SwingWorker<Void, Void> w = new SwingWorker<Void, Void>() {
 
            @Override
            protected Void doInBackground() throws Exception {
                System.out.println("I'm started!");
                return null;
            }
        };
 
        ExecutorService e = Executors.newSingleThreadExecutor();
        e.submit(w);
 
        e.shutdown();
    }
}

By the way, why NetBeans goes mad when I try to use diamond notation for SwingWorker declaration?
Here's the Exception thrown:
Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - incompatible types
required: javax.swing.SwingWorker<java.lang.Void,java.lang.V oid>
found: <anonymous javax.swing.SwingWorker<T,V>>
at polygon.Polygon.main(Polygon.java:10)

[Norm]

It executed the doInBackground() when I added this after the execute()

        Thread.sleep(150); //<<<<<<<<<< let above execute

[angstrem]

Hmmm, why's that so? Does that mean, that all the threads terminate when the main method returns?
And why, for example, this code executes the thread without sleeping?

    public static void main(String[] args) throws InterruptedException {
        new Thread(new Runnable(){
 
            @Override
            public void run() {
                System.out.println("I'm started!");
            }
 
        }).start();
    }

[Norm]

Read the API doc for the Thread class and its setDaemon() method.

[angstrem]

Oh, I see now... And how can I access the currently available worker threads and, perhaps, set some of them not to be a daemon? Where do they spawn and how are they accessed?

[Norm]

I don't know if or how to access those threads.

[angstrem]

I see... Thank you very much, Norm! Those stuff about daemon was really new for me. I'm glad that I understand threads a bit better after your explanations.