A hard question

[Adil El mouden]

hi,
Another question related to join method:

 
public class Joining {
    static Thread createThread(final int i, final Thread t1) {
        Thread t2 = new Thread() {
            public void run() {
                System.out.println(i+1);
                try {
                    t1.join();
                } catch (InterruptedException e) {
                }
                System.out.println(i+2);
            }
        };
        System.out.println(i+3);
        t2.start();
        System.out.println(i+4);
        return t2;
    }
 
    public static void main(String[] args) {
        createThread(10, createThread(20, Thread.currentThread()));
    }
}

Select the two correct answers.

1 The first number printed is 13.

2 The number 14 is printed before the number 22.

3 The number 24 is printed before the number 21.

4 The last number printed is 12.

5 The number 11 is printed before the number 23.

A: 2 and 4
why?
Thank you
[ July 19, 2005: Message edited by: Barry Gaunt ]

[Devender Thareja]

Originally posted by John Edwin:

public class Joining {
static Thread createThread(final int i, final Thread t1) {
Thread t2 = new Thread() {
public void run() {
System.out.println(i+1);
try {
t1.join();
} catch (InterruptedException e) {
}
System.out.println(i+2);
}
};
System.out.println(i+3);
t2.start();
System.out.println(i+4);
return t2;
}

public static void main(String[] args) {
createThread(10, createThread(20, Thread.currentThread()));
}
}

You see, the currentThread (main thread) is being passed to the createThread method.
Inside createThred method a new thread t2 is created.
The run method of t2 is implemented such as it waits for thread t1 to finish, because of t1.join statement.
The t1 actually is main thread.
T2 will finish last, always.
The last print statement in T2 is 12.

Hope it helps.

[Byron Foo]

a good question:

I think the sequence should be like this:
23 -> (21->14 or 14->21) -> 13 -> (11->14 or 14->11) -> 22 -> 12

[Rupak Khurana]

I dont think Thread.join() is covered in SCJP exam. Am I wrong ?