???
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
