no no no, I told you that the method getPropertyValue(p) can return NULL
if there is no such value for the given property p
That means what for your line
RDFNode physicsBestCat=indiv.getPropertyValue(bestcat);
?
Right, physicsBestCat can be NULL.
That means what for your line
Literal l1=physicsBestCat.asLiteral();
?
Right, asLiteral() must not be called if physicsBestCat is NULL.
> I mean Lorenz, is there any way, if there is no value, it do nothing (do
> not give exception) and if there is value, it should simply give us the
> value.
>
> if (l1!=null) supposed to work. :)
>
> Is it possible if we use something
>
> if (li==null)
> break;
>
> And we should get out of this snippet?
>
> Regards
>
> On Tue, Jan 17, 2017 at 4:10 PM, Lorenz B. <
> buehm...@informatik.uni-leipzig.de> wrote:
>
>> ???
>>
>> if there is no such value you can't get the value, I do not see the problem
>>> Hello Lorenz, thanks.
>>>
>>> Is there any way (alternative) to get this value as I need it further in
>> my
>>> operation?
>>>
>>> Regards
>>>
>>> On Tue, Jan 17, 2017 at 4:03 PM, Lorenz B. <
>>> buehm...@informatik.uni-leipzig.de> wrote:
>>>
>>>>> Hello Lorenz, believe me I have tried this before I write my problem
>> here
>>>>> in the forum but the problem persists. I also tried if s1!=null. .
>>>>>
>>>>> RDFNode physicsBestCat=indiv.getPropertyValue(bestcat);
>>>> But then the NullPointerException already occurs here.
>>>>
>>>> getPropertyValue can return NULL if there is no such value, that's also
>>>> explained in the Javadoc
>>>>> Literal l1=physicsBestCat.asLiteral();
>>>> You can't do it if physicsBestCat can be NULL
>>>>> if (l1!=null){
>>>>> String s1=l1.toString();
>>>>>
>>>>> if (s1=="Physics"){
>>>>> }}
>>>>>
>>>>> Regards
>>>>>
>>>>> On Tue, Jan 17, 2017 at 3:48 PM, Lorenz B. <
>>>>> buehm...@informatik.uni-leipzig.de> wrote:
>>>>>
>>>>>> Sorry, but the answer is too obvious, especially for a student in
>>>>>> computer science.
>>>>>>
>>>>>> What about checking if the literal is NULL before calling toString()?
>>>>>>
>>>>>>> Hello, I asked about this rule few days ago.
>>>>>>> String rule ="[rule1: ( ?x http://www.semanticweb.org/t/o
>>>>>>> ntologies/2016/7/myOWL#Physics_Preferred_Category ?cat1 )" +
>>>>>>> "( ?x http://www.semanticweb.org/t/ontologies/2016/7/myOWL#Chem_Pr
>>>>>>> eferred_Category ?cat2 )" +
>>>>>>> // "( ?x http://www.semanticweb.org/t/o
>>>>>>> ntologies/2016/7/myOWL#Geo_Preferred_Category ?cat3 )" +
>>>>>>> // "greaterThan(?cat1,?cat2), greaterThan(?cat1,?cat3)"
>>>>>>> + " -> (?x http://www.semanticweb.org/t/
>>>>>>> ontologies/2016/7/myOWL#BestCategory http://www.semanticweb.org/t/
>>>>>>> ontologies/2016/7/myOWL#BestCategory#Physics )]";
>>>>>>>
>>>>>>> The BestCategory is saved but as you know a user will select all the
>>>>>> three
>>>>>>> categories in the quiz, then the rule will execute, otherwise the
>> user
>>>>>> the
>>>>>>> user will have not the property BestCategory.
>>>>>>>
>>>>>>> When I want to extract the value of BestCategory for some operation,
>>>> for
>>>>>>> first time users to the quiz, it gives me Null Pointer Exception, and
>>>>>>> rightly so because the user has no value of BestCategory.
>>>>>>>
>>>>>>> RDFNode physicsBestCat=indiv.getPropertyValue(bestcat);
>>>>>>> Literal l1=physicsBestCat.asLiteral();
>>>>>>>
>>>>>>> //*here I think is the exception is*
>>>>>>> String s1=l1.toString();
>>>>>>>
>>>>>>> if (s1=="Physics"){
>>>>>>> }
>>>>>>>
>>>>>>> How should I handle this problem please?
>>>>>>>
>>>>>>> Much regards
>>>>>>>
>>>>>> --
>>>>>> Lorenz Bühmann
>>>>>> AKSW group, University of Leipzig
>>>>>> Group: http://aksw.org - semantic web research center
>>>>>>
>>>>>>
>>>> --
>>>> Lorenz Bühmann
>>>> AKSW group, University of Leipzig
>>>> Group: http://aksw.org - semantic web research center
>>>>
>>>>
>> --
>> Lorenz Bühmann
>> AKSW group, University of Leipzig
>> Group: http://aksw.org - semantic web research center
>>
>>
--
Lorenz Bühmann
AKSW group, University of Leipzig
Group: http://aksw.org - semantic web research center
