How does the assignment occur

Submitted by Annu on Fri, 09/19/2008 - 20:19.

Hi,
Can you please tell me how does this piece of code work
int a[] = new int[4];
void aMethod()
{
int b = 0 , index;
a[a[b]] = a[b] = b = 2;
index = ??? ;
System.out.println(a[index]);
}
What value assigned to the variable index will print a non zero result?

Thanks in advance
Annu

‹ Autoboxing And Boxing Why doesn't it say ambiguous reference ›
Submitted by Ashish.Hareet on Sat, 09/20/2008 - 06:30.

Annu,

Before I can answer your question, we require that you indicate where your question was obtained from(as indicated in the forum posting guidelines) - http://www.irixtech.com/content/forum-posting-guidelines-0

Since some mock exams give out real exam questions, we like to make sure that we're not discussing real exam questions. Doing so is a copyright violation & for any exam takers it would amount to cheating.

Thanks
Ashish Hareet

Submitted by Annu on Wed, 09/24/2008 - 17:30.

Hi,
I obtained the above question when I was solving the mock paper from the following site.
http://www.javablackbelt.com/QuestionnaireDefDisplay.wwa?questPublicId=0...
And this link I got it from http://faq.javaranch.com/java/ScjpMockTests.

Thanks and regards
Annu

Submitted by Ashish.Hareet on Wed, 09/24/2008 - 18:23.

Thanks for providing the reference, I'm at work right now, expect an answer sometime in the next 10 hrs or so.

Ashish Hareet

Submitted by Ashish.Hareet on Thu, 09/25/2008 - 03:23.

Since int a[] is a member variable it'll get inititalized to the default values, so
a[0] = 0
a[1] = 0
a[2] = 0
a[3] = 0

Now referring to JLS 15.2.6.1 -in particular note the 2nd bulleted point, here's how we can evaluate a[a[b]] = a[b] = b = 2;

  • We need to resolve all the variables before assignment can proceed
  • First evaluate a[a[b]] as follows - a[a[0]] = a[0]
  • Then we evaluate a[b] which is a[0]
  • Now, we start the assignment from the right
  • So a[a[b]] = a[b] = b = 2; becomes a[0] = a[0] = b = 2

Finally what we're left with is b = 2 and a[0] = 2, which means that index has to be 0, cause that was the only index that got set as a result of the assignment.

HTH
Ashish Hareet