Re: What does this Snippet Do ? Interview Question!!!!!!!!!

From:
Christian <fakemail@xyz.de>
Newsgroups:
comp.lang.java.programmer
Date:
Sun, 15 Apr 2007 01:08:21 +0200
Message-ID:
<46215efa$0$18220$9b622d9e@news.freenet.de>
adil.fulara@gmail.com schrieb:

Hi,

I got the following question in a interview test that i gave and i was
unable to answer it.

========================================================================
 What does the following program print?

public class Initializer
{
    private static boolean initialized = false;
    static
    {
        Thread t = new Thread( new Runnable()
        {
            public void run()
            {
                initialized = true;
            }
        } );

        t.start();
        try
        {
            t.join();
        }
        catch (InterruptedException e)
        {
            throw new AssertionError(e);
        }
    }

    public static void main(String[] args)
    {
        System.out.println(initialized);
    }
}

(provide the exact output for this question, there are no choices)
=================================================================

At the time of the test, i just couldnt figure if the code would be
executed or not since in Main, there was no instance of the object
created.

Any help on the question ?

Also where could i find such tricky snippets of code so that icould
test myself and in the process improve my java knowledge.

Thank You.


What happens is:

1. initialized is initialized false by the thread loading the class

2. another Thread is created an run that will set initialized to true

3. with join() the thread loading the Initializer class will wait for
this Thread to finish his job..

4. the main method is executed and it prints out "true".

afaik the dying of the thread and waiting for it with join guarantees a
proper "happens before" relation of the event of changing the
initialized variable to true and printing it.

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