Thread Doubt

[suresh kamsa]

class MyThread extends Thread {
    public void run() {
      for (int count = 1, row = 1; row < 20; row++, count++)   // loop1
      {
           for (int i = 0; i < count; i++)
                System.out.print ('*');
           System.out.print ('\n');
      }
   }
}
class ThreadDemo {
    public static void main(String[] args) {
       MyThread mt = new MyThread();
       mt.start(); // l1
      for (int i = 0; i < 50; i++)  // loop2
           System.out.println ("i = " + i + ", i * i = " + i * i);
   }
}
  

Why the output is
i = 0, i * i = 0
i = 1, i * i = 1
i = 2, i * i = 4
*
**
***
****
and so on. After control coming to line1 how the control flows? Why is it not completing loop1 first? doing simultaneously both?. This is becuase of Threads I know but someone explain me pl.
Thanks.

[Barkat Mardhani]

At line1 control splits in two threads each executing a loop. If you reduce the no. of iteration in each loop to (say) 5 and run this programs quite a few time, you will see that output is unpredictable because both loops are executing at the same time....
[ September 26, 2002: Message edited by: Barkat Mardhani ]
[ September 26, 2002: Message edited by: Barkat Mardhani ]

[Bishal P]

Every process in java is executed in a thread. So when you type "java ThreadDemo" a thread is atrted which executes the code inside main. Lets call this T1.
Now when you say "mt.start()" the thread no.2 (T2) starts up parallely. After this there is no certainity to the execution life time of the two threads. They don't share any variable and hence there is no scope of waiting. And it is not certain that the output will be same always. Infact i executed the same program thrice and got totally different result the third time.
The cpu is shared by the two threads according to Java scheduling system which is based on priority.