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Servlet Error

Posted on 2002-04-30
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Last Modified: 2013-11-24
I have a quick question.
What is the difference between the following:
   String test = req.getParameter("Something").trim();
and
   String test = "";
   test = req.getParameter("Something").trim();

If Something is not in the querystring I get an error.
For some reason when i use the first example I get a nullpointer exception. If I use the second example it works with out a problem. I am using JRun 2.3.

Thank You in advance.
Kent
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Question by:kmurphy7
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by:CEHJ
ID: 6981593
listening...
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by:jamoville
ID: 6981652
When you run the second example and "Something" is not in the querystring (the one you indicate works ok) what is the value of test?
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by:kmurphy7
ID: 6981663
test = ""

 If I am not mistaking there is a difference between "" and null. Is this correct.
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by:CEHJ
ID: 6981669
You're correct
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by:jamoville
ID: 6981676
I'm not using JRun but I get a null pointer for both which is what you would expect to get.  There is a difference between "" and null. The line req.getParameter("Something") should be returning null.  When the trim() is applied to the null value returned you should get a null pointer exception.  This is what I'm seeing, but maybe JRun behaves differently.
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by:Jan Louwerens
ID: 6981733
both are wrong. You want to use:

   String test = req.getParameter("Something");
   if (test != null)
      test = test.trim();
// else
//    test = "";  // maybe you want a default value if it's not specified
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by:jamoville
ID: 6981869
jlouwere :

The code you wrote would work but why kmurphy7 is not getting a null pointer exception with the second example is the real question that should be answered.
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by:jerelw
ID: 6982034
I don't believe that the code posted is the actual sequence of events.

please post the actual block of code with the issue, and we can see when and where values are being set and if the code is in a try - catch.
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by:bobbit31
ID: 6982119
> why kmurphy7 is not getting a null pointer exception with the second
example

b/c it is not a null object... it is a String object of zero length (like an empty vector for example)
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by:CEHJ
ID: 6982129
>>b/c it is not a null object...

It *should* be after it has been assigned null (which is the case in the second example). Otherwise the assignment has not worked.
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bobbit31 earned 50 total points
ID: 6982134
is this the second example?
  String test = "";
  test = req.getParameter("Something").trim();

if so, it is not being assigned null, it is being assigned to a zero length string
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by:CEHJ
CEHJ earned 50 total points
ID: 6982154
Ah. It's becoming clear. Both I and bobbit31 are right:

>> it is not being assigned null, it is being assigned to a zero length string

>>Otherwise
the assignment has not worked.

The assignment never gets made, as req.getParameter("Something").trim(); throws an exception. Therefore 'test' holds its original value, i.e. a zero length string! Thanks for the prompt bobbit31
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by:bobbit31
ID: 6982158
no prob ;)
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by:CEHJ
ID: 6982168
kmurphy7 - we've solved the mystery I think!
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by:girionis
ID: 8682739
No comment has been added lately, so it's time to clean up this TA.

I will leave a recommendation in the Cleanup topic area that this question is:

- points to bobbit31

Please leave any comments here within the
next seven days.

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER !

girionis
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by:CEHJ
ID: 8683207
hmmmmmmm.
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