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. < [email protected]> 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. < > > [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 > >> > >> > -- > Lorenz Bühmann > AKSW group, University of Leipzig > Group: http://aksw.org - semantic web research center > >
