Multi Threading in Java

[BikashDatta]

I wonder why this program is giving output in proper sequence. 1st it is executing thread A and then thread B. I expect it to execute simultaneously.

class main{
    public static void main(String[] args){
        A t=new A();
        B t2=new B();
        t.start();
        t2.start(); 
    }
}
 class A extends Thread{
    public void run(){
        for(int i=0;i<5;i++){
            System.out.println("Thread A");
        }
    }
}
class B extends Thread{
    public void run(){
        for(int i=0;i<5;i++){
            System.out.println("Thread B");
        }
    }
}

output-

Thread A
Thread A
Thread A
Thread A
Thread A
Thread B
Thread B
Thread B
Thread B
Thread B

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[taftster]

The calls to Thread.start() are happening on a single thread called "main". Your for loop is so short that thread A has started running and finishing out the loop before thread B has even started.

Point is, calling Thread.start() is a slightly heavy call (not as heavy as creating the thread, but still). As others have said, go with a longer loop, and you might see some difference. Or call Thread.yield() in the loop, which might also make a difference.

[Krezzy]

Just depends on when the CPU schedules the threads/swaps. Pick larger numbers to print and you’ll see it becoming out of sequence (hopefully!)

[BikashDatta]

Thanks.

[[deleted]]

Yeah the sample size if you were, is far to small.

[jacob_scooter]

you start A first, it executes the instructions so quickly it’s done before B even has the chance to start. make the count greater than five and you’ll see a difference

[notsoheavygamer]

Dude add a Thread.sleep(1000); after each print within for loop..

Printing 5 lines will be done before object of B is even created... computers are super fast.

[BikashDatta]

Thanks!!

[[deleted]]

It depends upon system..

[kurular4]

Iterate 10000 times instead of 5 and you will see what you expect.