Daemon and User threads

TestThreads.java

package testex;

/**
 * Notice the difference between daemon (background) threads and non-daemon (user) threads
 * - Finally blocks are not executed for daemon threads
 * - JVM is concerned about user threads only
 * - JVM exits when all user threads are completed in other words JVM waits for user threads to run to completion
 * - JVM doesn't wait for daemon threads - simply kills it when JVM is ready to exit (or killed by user action)
 * - If any clean up needs to be done for daemon threads (works for user threads also) put them as a shutdown hook
 * @author johne
 *
 */
public class TestThreads {

	public static void main(String[] args) throws InterruptedException {
		System.out.println(Thread.currentThread().getName() +" starting");
		MyThread t1 = new MyThread();
		t1.setDaemon(true);
		t1.setName("Daemon thread");
		MyThread t2 = new MyThread();
		t2.setName("User thread");
		t1.start();
		t2.start();
		Thread.sleep(2000);
		System.out.println(Thread.currentThread().getName() +" exiting");
		
		Runtime.getRuntime().addShutdownHook(new Thread() {
		    public void run() {
	            System.out.println("Shutdown hook called");
		    }
		});
	}

}

class MyThread extends Thread {
	@Override
	public void run() {
		try {
			int i=1;
			while (i<=5) {
				if (Thread.currentThread().isDaemon()) {
					System.out.println("i="+ i + " ... "
							+ Thread.currentThread().getName());
					Thread.sleep(2000);
				} else {
					System.out.println("i="+ i + " ... "
							+ Thread.currentThread().getName());
					Thread.sleep(1000);
				}
				i++;
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		} finally {
			System.out.println("Thread exiting ... "
					+ Thread.currentThread().getName()); // never called
		}

	}
}