This week's book giveaway is in the Servlets forum.
We're giving away four copies of Murach's Java Servlets and JSP and have Joel Murach on-line!
See this thread for details.
The moose likes Programmer Certification (SCJP/OCPJP) and the fly likes Question on Precedence/Assignment Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login


Win a copy of Murach's Java Servlets and JSP this week in the Servlets forum!
JavaRanch » Java Forums » Certification » Programmer Certification (SCJP/OCPJP)
Bookmark "Question on Precedence/Assignment" Watch "Question on Precedence/Assignment" New topic
Author

Question on Precedence/Assignment

Dominic Choo
Greenhorn

Joined: Jan 30, 2003
Posts: 26
Hi,
I came across this question:
--------------------------------------
int i = 0;
int[] a = {3,6};
a[i] = i = 9; // line 3
System.out.println(i + " " + a[0] + " " + a[1]);
Select the one right answer:
a) Raises ArrayIndexOutOfBoundsException
b) Prints "9 9 6"
c) Prints "9 0 6"
d) Prints "9 3 6"
e) Prints "9 3 9"
I would like to know why the answer is b) not a) ?
Thank you.
Rgds.
M Huang
Greenhorn

Joined: Jun 18, 2003
Posts: 9
I'm not sure. It looks confusing. I do know that the [] operator has higher precedence than the = operator. So it's probably because expression a[i] gets evaluated first, locking in the fact that you will store whatever it is into a[0]. And then i gets 9, and a[0] gets 9.
OK, now that I've thought about it for a bit, drew a parse tree, and thought about some other examples (int x = 3*3 + 4 is the simplest that comes to mind), I am absolutely sure that that's the correct explanation.
How tricky! Where did you get such a tricky question?
[ June 18, 2003: Message edited by: M Huang ]
Barkat Mardhani
Ranch Hand

Joined: Aug 05, 2002
Posts: 787
Here is how I look at:
int i = 0;
int[] a = {3,6};
a[i] = i = 9; // line 3
System.out.println(i + " " + a[0] + " " + a[1]);
1. First assignment (=) takes precedence over second assignment (=) .... left to right rule
2. a[i] = i
as i = 0
a[0] = 0
3. Now second assignment:
i = 9
4. So println will give: 9 0 6
Hope this makes sense...
Thanks
Barkat
Veena Pointi
Ranch Hand

Joined: Jun 20, 2002
Posts: 442
I think following link discusses the same
http://www.coderanch.com/t/242181/java-programmer-SCJP/certification/Operator-precedence
veena


SCJP1.4
"Continuous effort - not strength or intelligence - is the key to unlocking our potential."
*Winston Churchill
Damien Howard
Ranch Hand

Joined: Apr 01, 2003
Posts: 456
but according to Dominic the answer was b not c or a. So can someone explain this?
[ June 18, 2003: Message edited by: Damien Howard ]
Veena Pointi
Ranch Hand

Joined: Jun 20, 2002
Posts: 442
Originally posted by Damien Howard:
but according to Dominic the answer was b not c or a. So can someone explain this?
[ June 18, 2003: Message edited by: Damien Howard ]

Follow this link ,it is very clearly explained in this discussion.
http://www.coderanch.com/t/242181/java-programmer-SCJP/certification/Operator-precedence
James Chegwidden
Author
Ranch Hand

Joined: Oct 06, 2002
Posts: 201
Let me try:

Assignment is from right to left not left to right
What does assignment do "replace"
i= 9 a[0] = 9 and a[1] = 6 B right?
[ June 18, 2003: Message edited by: James Chegwidden ]

Author and Instructor, my book
Dominic Choo
Greenhorn

Joined: Jan 30, 2003
Posts: 26
I get this question from Khalid's Book.
It's really tricky.
Brian Joseph
Ranch Hand

Joined: May 16, 2003
Posts: 160
Read the thread from the link above. Marlene describes how to evaluate the = expression. You need to take the expression through a few passes. First identify where the parenetheses go, then evaluate left to right.
 
I agree. Here's the link: http://aspose.com/file-tools
 
subject: Question on Precedence/Assignment
 
Similar Threads
doubt in multiple assignment !
// simple Question
question from KAM
Question by Sreenivasa Kumar Majji
Arrays doubt