Threads and Sync

[podonga poron]

A taked this code from K&B book, WHY IT THROWS Total is: 4950

public class ThreadA {
    public static void main(String [] args) {
       ThreadB b = new ThreadB();
       b.start();
       
       synchronized(b) {
          try {
             System.out.println("Waiting for b to complete...");
            b.wait();
          } catch (InterruptedException e) {}
          System.out.println("Total is: " + b.total);
       }
    }
 }
 
 class ThreadB extends Thread {   
    int total; 
    @Override
    public void run() {
        synchronized(this){
          for(int i=0;i<100;i++) {
             total += i;
          }
          notify();
       }
    }
 }
 

[ June 20, 2008: Message edited by: Campbell Ritchie ]

[Keith Nagle]

Because, for each int i,
your adding it to total.
Total is given its default value for type int
(because its an instance variable remember).
So, i is added to this each time.
What is (0 + 1 + 2 + 3 + 4 + ... + 99)?
=> 4950!
best regards.
K

P.S be careful with your wording.
It doesn't throw total. It prints it!
[ June 20, 2008: Message edited by: Keith Nagle ]

[Priety Sharma]

Hi,

Good use of wait and notify to let the ThreadB execute before ThreadA completes.

But you could have done the same without using wait() and notify() and just replacing b.wait() with b.join().


Also the topic for the question could have been "Loop output" instead of "Threads and Sync".

Just an observation.

Regards,
Priety.