NullPointerException when checking for null value

[thorny pawn]

private void verwerkKeuze1() { List<ArtikelDTO> artikelDTOS = domeinController.geefArtikelsUitBestellingMetBestelNummer( geefKeuze("Geef bestelnummer: ",1000, 10000)); if (artikelDTOS != null) { drukAfOpScherm(artikelDTOS); } else { System.out.print("Geen artikels aanwezig"); } }

Why am I getting a NullPointerException when I'm checking for a null value. This Exception is only obviously only thrown when artikelDTOS is null.

[nimble snow]

<@&987246399047479336> please have a look, thanks.

[viscid stirrup]

you ar echeking if the list is null or not, maybe its elements are null or it is empty?

[thorny pawn]

If its empty, doesn't it just result in the object being null? Maybe I'm getting somewhat confused because of the debugger, intellij shows ArtikelDTOS: null.

[viscid stirrup]

no an empty list is not a null list

just like an empty string "" is not null

you can do something like artikelDTOS != null && !artikelDTOS.isEmpty()

[viscid stirrup]

yes so then it shouldnt execute drukAfOpScherm(artikelDTOS); but instead print the debug message. Does it not do that?

[thorny pawn]

Nope it throws the exception. I'm starting to think my IDE is having some issues with byte and source code

[viscid stirrup]

can you send the full stacktrace of the exception?

[thorny pawn]

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.List.isEmpty()" because "dtos" is null
at cui.BestellingApplicatie.drukAfOpScherm(BestellingApplicatie.java:50)
at cui.BestellingApplicatie.verwerkKeuze1(BestellingApplicatie.java:45)
at cui.BestellingApplicatie.start(BestellingApplicatie.java:29)
at main.StartUp.main(StartUp.java:12)
Disconnected from the target VM, address: '127.0.0.1:50653', transport: 'socket'

Process finished with exit code 1

[viscid stirrup]

can you also send the drukAfOpScherm1 method?

[thorny pawn]

private void drukAfOpScherm(List<ArtikelDTO> dtos) { for (ArtikelDTO dto : dtos) { System.out.printf("Artikel %s in %c, padnr %d. Weegt %.3f kg. %s.%n", dto.artikelCode(), dto.gang(), dto.padnr(), dto.gewicht(), dto.status()); } }

I'll be back in 20m

[viscid stirrup]

seems really odd. Maybe you can workaround it by adding a null check in the drukAfOpScherm1 method, but it should work as it is now

[thorny pawn]

I think its just some issue with the ide itself rather than the code.

Thanks for taking the time though.

[viscid stirrup]

ik this may sound dumb but you are sure you've saved the file?

[thorny pawn]

I had to compile manually for some reason, its working now.

[viscid stirrup]

oh well at least it works