About Question enthuware.ocpjp.v8.2.1391 :

Help and support on OCA OCP Java Programmer Certification Questions
1Z0-808, 1Z0-809, 1Z0-815, 1Z0-816, 1Z0-817

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sandeshchaudhari
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About Question enthuware.ocpjp.v8.2.1391 :

Post by sandeshchaudhari »

When i run this program it prints nothing in the o/p but answer given is 0 2 4. Can you please tell me why this?

admin
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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by admin »

Did you read the explanation? It explains exactly what you are asking.
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runnerdave
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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by runnerdave »

Can you please explain why the results are always ordered?

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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by admin »

The main thread prints the value of data variable of each thread one by one in the for loop. So irrespective of what the value of data variable is for any thread, the first value printed will be the data value of the first thread, second value printed will be the data value of the second thread, and the third value printed will be the data value of the third thread.
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shatterblast
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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by shatterblast »

Will you please explain why the output is always in increments of 2?

I try the following code, and the output comes out as 0 2 4 6 8. Thank you for your time.

Code: Select all

    ...  //Other code.
    
    public static void main(String[] args) throws Exception
    {
        Test[] jta = new Test[5];
        for(int i=0; i<5; i++) {
            jta[i] = new Test(i); jta[i].start();
        }
        for(Test jt : jta) {
            if(jt.isDone()) System.out.println(jt.getData());
        }
    }
    
    ...  //Whatever else.

admin
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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by admin »

Because of the statement data += data; in run() method. data += data; is mathematically same as data = 2*data.
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zukras
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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by zukras »

Hi,

I don't understand when it might print 0, 1, 2.
  1. It will print something only if jt.isDone() returns true.
  2. jt.isDone() returns true only when run() is executed.
  3. When run() is executed data is always equals to 2*data
What I am missing in this question?

Thanks

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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by admin »

You are not missing anything. It can't print 0, 1, 2. The question does not say that it may print 0, 1, 2 either.
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prashantjain25
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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by prashantjain25 »

This got me confused it should also print 0,1,2 but it never does that. it prints all of these
0
0,2
0,4
0,2,4
but never 0,1,2 why?

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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by admin »

You will need to read the explanation. It explains exactly why 0 1 2 cannot be printed.
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moostebring
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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by moostebring »

One question though. Hypothetically, if the first thread in the list for whatever reason is not ready upon the evaluation of the if(isDone()) method, it get's skipped and 2 - 4 would get printed right? Is that also the reason why the answers state 0 2 4 is a "possible" solution?

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Re: About Question enthuware.ocpjp.v8.2.1391 :

Post by admin »

That's right. But that is not the reason for 0 2 4 .
0 2 4 will be printed if all three threads are done before the main thread is able to execute the second loop.
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