isAlive() method

[Cody Beth]

Hi All,
Need to know about Thread.isAlive() method
As we know that we cannot re-start a thread once it has executed a run method, i.e., it is not alive after its dead.
Check the code below..

 public class TestThread {
    public static void main(String[] args) throws Exception {
        Runnable objRun = new MyRunnable();
        Thread t1 = new Thread(objRun);
        System.out.println("1 = " + t1.isAlive());
        t1.start();
        System.out.println("2 = " + t1.isAlive());
        t1.join();
        System.out.println("3 =" + t1.isAlive());
        t1.start();
        System.out.println("4 = " + t1.isAlive());
        Thread.sleep(2000);
    }
}
class MyRunnable implements Runnable {
    public void run() {
        System.out.println(" In run method");
    }
}

the output of the code is :
1 = false
2 = true // as start method called
In run method
3 = false // run method is completed
4 = true ??? This is showing the thread is alive but run method did not execute again.

Regards,
Cody

[Jose Botella]

Thanks Cody. That makes isAlive() method a bit less reliable.

[Barkat Mardhani]

But Jose, shouldn't second start give a runtime error?

[Alton Hernandez]

Originally posted by Barkat Mardhani:
But Jose, shouldn't second start give a runtime error?

That's a known bug in the JVM.

[Kalai Ganesh]

Hai Cody,
When I executed the same program the output was
1= false
2= true
3= false
4= false
Probably the second start() didn't make the thread alive here. Why is this difference? Anyway this shouldn't be platform dependent. Am I right?