return() and System.exit()

[Jian Yi]

what is the diff between return() and System.exit() in main()?
Thanks,
Jenny

[Corey McGlone]

Try this example:

public class ReturnTest extends Thread
{
   public static void main(String[] args)
   {
      ReturnTest t = new ReturnTest();
      t.start();
      //return;        // 1
      System.exit(0);  // 2
   }
 
   public void run()
   {
      while(true);
   }
}

If you run this program as is, the application will terminate immediately. However, if you comment out line 2 and uncomment line 1, you'll see that the application gets caught in an infinite loop.
If you take a look at the API Spec for System, you can see the description of the exit method states:

Terminates the currently running Java Virtual Machine...

This means that your application will terminate, no matter what is happening. A return, however, signifies, the successful completion of a method.
I hope that helps,
Corey

[Jian Yi]

Thanks a lot, Corey! Your answers are always so clear!