Daemon Threads

An application doesn't end until every non-daemon thread in it has stopped. So how do you make a deamon thread?

Non-Daemon Thread


// ThreadDemo1.java


// Spawn a non-daemon thread that takes a while to get done.  The
// application does not end until the thread has finished.

class ThreadDemo1 extends Thread
  {


  // Main.  Start the thread, then count to five.

  public static void main (String[] args)
    {
    Thread thread = new ThreadDemo1();
    thread.start();
    for (int i = 0; i < 5; i++)
      {
      System.out.println ("Main: " + i);
      sleep (1000);
      }
    System.out.println ("Main done");
    }


  // This method is run as a separate thread.  Count to 10.

  public void run()
    {
    for (int i = 0; i < 10; i++)
      {
      System.out.println ("Thread: " + i);
      sleep (1000);
      }
    System.out.println ("Thread done");
    }


  // Sleep for so-many milliseconds.

  static void sleep (int msec)
    {
    try
      {Thread.currentThread().sleep (msec);}
    catch (InterruptedException e)
      {}
    }


  };

See also

Basic Threads

Daemon thread


// ThreadDemo2.java


// Spawn a daemon thread that takes a while to get done.  The application
// ends as soon as the main thread ends, even though the daemon thread is
// not done.

class ThreadDemo2 extends Thread
  {


  // Main.  Start the thread, then count to five.

  public static void main (String[] args)
    {
    Thread thread = new ThreadDemo2();
    thread.setDaemon (true);
    thread.start();
    for (int i = 0; i < 5; i++)
      {
      System.out.println ("Main: " + i);
      sleep (1000);
      }
    System.out.println ("Main done");
    }


  // This method is run as a separate thread.  Count to 10.

  public void run()
    {
    for (int i = 0; i < 10; i++)
      {
      System.out.println ("Thread: " + i);
      sleep (1000);
      }
    System.out.println ("Thread done");
    }


  // Sleep for so-many milliseconds.

  static void sleep (int msec)
    {
    try
      {Thread.currentThread().sleep (msec);}
    catch (InterruptedException e)
      {}
    }


  };

The Applications' Outputs

ThreadDemo1      ThreadDemo2
(Non-daemon)      (Daemon)
------------     -----------
Main: 0          Main: 0
Thread: 0        Thread: 0
Main: 1          Main: 1
Thread: 1        Thread: 1
Main: 2          Main: 2
Thread: 2        Thread: 2
Main: 3          Main: 3
Thread: 3        Thread: 3
Main: 4          Main: 4
Thread: 4        Thread: 4
Main done        Main done
Thread: 5
Thread: 6
Thread: 7
Thread: 8
Thread: 9
Thread done

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