start() and join() in thread

[ajith srikukan]

  class Account {
    private Integer number = 0;
    public synchronized void setNumber(Integer number) {
        this.number = number;
    }
    public synchronized Integer getNumber() {
        return number;
    }
}

class Client extends Thread {
    Account account;
    public Client(Account account) {
        this.account = account;
    }
    public void run() {
        for (int i = 1; i <= 1000; i++) {
            account.setNumber(account.getNumber() + 1);

        }
    }
}

public class Test {
    public static void main(String[] args) throws Exception {
        Account account = new Account();
        Client one = new Client(account);
        Client two = new Client(account);
 
    //add code here
        	
        System.out.println(account.getNumber());
    }
}
  

can anyone explain the reason behind the output ...

1. one.start();

//output "0"

2.one.start();
two.start();

//output "0"

3. one.start();
two.start();
one.join();
two.join();
//output varies between 1000 and 2000

[Ankit Garg]

Hi Ajith, welcome to Javaranch.

Ajith at ranch we have a rule that if you post a code from a mock exam, then you've to QuoteYourSources. So please tell us from where did you take that question so that we can help you...

[Ryan Beckett]

In scenarios 1 and 2, the main method executed first, and in the 3rd it waits until both client threads are finished. If you run scenario 1 and 2 more, the output should change. Threads are unpredictable.

[ajith srikukan]

Ankit Garg wrote:Hi Ajith, welcome to Javaranch.

Ajith at ranch we have a rule that if you post a code from a mock exam, then you've to QuoteYourSources. So please tell us from where did you take that question so that we can help you...

http://nikojava.wordpress.com/2008/09/08/scjp-mock-exam-for-threads/
question 58

[ajith srikukan]

Ryan Beckett wrote:In scenarios 1 and 2, the main method executed first, and in the 3rd it waits until both client threads are finished. If you run scenario 1 and 2 more, the output should change. Threads are unpredictable.

thanks Ryan, i got the idae .....

one more thing ... in the 3rd scenario the main thread will wait until other two threads finish and both methods are synchronized so each thread(one and two) loop will run 1000 times. this implies , the loop will run 2000 times but the output is between 1000 and 2000 why is that?