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Why am i getting NullPointerException but runs properly

Gaurav Wadhwani
Ranch Hand

Joined: Sep 21, 2010
Posts: 68
What i am trying to make is a quiz. For Fetching the records from the same location from where the user quits, I need to maintain a session. So i am using a attribute "nq" which increments each time a question is answered. However, the initial value of nq will be null so i change it to 1 to fetch the first record. And increment it then on.

I get NullPointerException. If i get it only the first time I execute its understandable because of the above reason but If I close and start again even before session expires, i get it again. Why so?
There should be no NullPointerException again as it can fetch the value of nq during the session.
Also am i doing this the right way?

Bear Bibeault
Author and ninkuma
Marshal

Joined: Jan 10, 2002
Posts: 61654
    
  67

You could test it for null, and set it to some initial value if so.

P.S. Do you really think that "nq" is a good name for anything?

P.P.S. Instance variables in a servlet? Generally bad news!


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Nikhil Pasupukuntla
Greenhorn

Joined: Jun 04, 2009
Posts: 21
Hi Gaurav,

If you are using any IDE like eclipse or NetBeans you can debug your program by adding NullPointerException breakpoint and see where the problem is.


Nikhil Pasupukuntla
SCJP 1.5 | OCPJWCD 1.5
Stefan Evans
Bartender

Joined: Jul 06, 2005
Posts: 1018
Gaurav Wadhwani wrote:If i get it only the first time I execute its understandable because of the above reason
but If I close and start again even before session expires, i get it again. Why so?


What defines a session?
Most often it is stored in a session cookie which is lost when you finish the browser session.

So closing the window and starting again issues you a new session, even if the old one is still active, because it knows nothing about the old one.
Gaurav Wadhwani
Ranch Hand

Joined: Sep 21, 2010
Posts: 68
Sorry for the very late reply everyone.

@Bear Bibeault
Do you really think that "nq" is a good name for anything?
Yes its a dumb name...only for testing purposes.

Instance variables in a servlet? Generally bad news!
Yes, and what i want in my application is to give one DB connection to every user but i dont know how to give a DB connection in a session. Please help


@Nikhil Pasupukuntla
I learnt how to add a breakpoint but not how to test it. Please help.


@Stefan Evans
If the session cookie is lost on closing and restarting then how is it possible that i get to continue with the same question i left at. If i close on question 4 -> close and start it again i get question 5 . So it has session and the cookie available why then a null pointer Exception?
Amit Ghorpade
Bartender

Joined: Jun 06, 2007
Posts: 2716
    
    6

Bear said something about checking it for null.


SCJP, SCWCD.
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Gaurav Wadhwani
Ranch Hand

Joined: Sep 21, 2010
Posts: 68
hmm, That what i did now and found the error.

It was line 95 , it had to be


What a time waste, kept thinking there is some logical error and it was some typing mistake. Anyway finally found and learned a lesson Thank you guys
Shanky Sohar
Ranch Hand

Joined: Mar 17, 2010
Posts: 1051

Gaurav Wadhwani wrote: What a time waste, kept thinking there is some logical error and it was some typing mistake. Anyway finally found and learned a lesson Thank you guys


This happens many of the times..and it shooks our head..by thinking where is the mistake...


SCJP6.0,My blog Ranchers from Delhi
 
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