null pointer at run time

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a - 14 May 2008 09:59 GMT

When I run my program the first time, the cookie must be a null.
So, for the following statement, why I will get null pointer exception at
runtime? How can I fix it?

if(cookie.getValue()!=null){
...
}else{
...
}

Thanks

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Sabine Dinis Blochberger - 14 May 2008 10:40 GMT

> When I run my program the first time, the cookie must be a null.
> So, for the following statement, why I will get null pointer exception at
[quoted text clipped - 5 lines]
> ....
> }

Check if cookie is null first, before trying to access members of it
(like getValue).
For example

if (cookie != null && cookie.getValue() != null)

Note that this counts on the order of evaluation of logical statements,
and if you're not sure, use two if statements.

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Sabine Dinis Blochberger

Op3racional
www.op3racional.eu

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Lew - 14 May 2008 13:09 GMT

>> When I run my program the first time, the cookie must be a null.
>> So, for the following statement, why I will get null pointer exception at
[quoted text clipped - 14 lines]
> Note that this counts on the order of evaluation of logical statements,
> and if you're not sure, use two if statements.

If you're not sure of what?

Signature

Lew

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Sabine Dinis Blochberger - 14 May 2008 13:19 GMT

>>> When I run my program the first time, the cookie must be a null.
>>> So, for the following statement, why I will get null pointer
[quoted text clipped - 17 lines]
>
> If you're not sure of what?

The order of evaluation. Suppose someone wants a "fast" fix, just be
verbose and don't guess (if you don't want to look it up). *shrugs*

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Sabine Dinis Blochberger

http://www.blochberger.de

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Lew - 15 May 2008 04:41 GMT

>>> Note that this counts on the order of evaluation of logical statements,
>>> and if you're not sure, use two if statements.

Lew wrote:

>> If you're not sure of what?

> The order of evaluation. Suppose someone wants a "fast" fix, just be
> verbose and don't guess (if you don't want to look it up). *shrugs*

Anyone more than six months into Java should be aware of the order of
evaluation. Certainly they should be aware that || and && are "early-out"
operators and | and & are not. How could someone claim to be any kind of
experienced Java programmer and not even know the operators?

Signature

Lew

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Roedy Green - 14 May 2008 15:55 GMT

On Wed, 14 May 2008 10:40:32 +0100, Sabine Dinis Blochberger
<no.spam@here.invalid> wrote, quoted or indirectly quoted someone who
said :

>Note that this counts on the order of evaluation of logical statements,
>and if you're not sure, use two if statements.

That order is 100% guaranteed. You can count on it. See
http://mindprod.com/jgloss/mccarthyandoperator.html
and
http://mindprod.com/jgloss/mccarthyoroperator.html

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Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com

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Roedy Green - 14 May 2008 14:42 GMT

>if(cookie.getValue()!=null){

cookie might be null too.

So you have to say

if ( cookie== null || cookie.getValue() == null )

Signature

Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com

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null pointer at run time

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