Why can't a Java Thread object be restarted?

It's arguably much easier to reason about (and probably implement) a Thread that simply executes its given task exactly once and is then permanently finished. To restart threads would require a more complex view on what state a program was in at a given time.

So unless you can come up with a specific reason why restarting a given Thread is a better option than just creating a new one with the same Runnable.

class ThreadExample {

    public static void main(String[] args){

           Thread myThread = new Thread() {

                  public void run() {

                        for(int i=0; i<3; i++) {

                               try {

                                      sleep(100);

                               } catch(InterruptedException ie) {

                               }

                               System.out.print(i+", ");

                        }

                        System.out.println("done.");

                  }

           };

           myThread.start();

           try {

                  Thread.sleep(500);

           } catch(InterruptedException ie) {

           }

           System.out.println("Now myThread.run() should be done.");

           // <-- causes java.lang.IllegalThreadStateException

           myThread.start();

    }

}

Output:

0, 1, 2, done.

Now myThread.run() should be done.

Exception in thread "main" java.lang.IllegalThreadStateException

   at java.lang.Thread.start(Unknown Source)

    at com.threads.status.ThreadExample.main(ThreadExample.java:30)