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. < [email protected]> 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. < > > [email protected]> 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 > >
