Question

I have this recursive method:

 public Hund getMor(int id) {
    Hund barn = getHund(id);
    int idMor = barn.getId_mor();
    Hund mor = getHund(idMor);

    return mor;
}

public String getMorTre(int id) {
    if (id == 0) {
        return null;
    }
    if (!existHund(id)) {
        return "Hunden du søkte etter finnes ikke";
    } else {
        if (id == 0) {
            return null;
        } else {
            Hund mor = getMor(id);
            MinRamme.jta.append(mor.toString() + "\n");
            int morId = mor.getId();
            return getMorTre(morId);
        }

    }
}

I have tried to remove the nullpointer by returning null if the id is 0 but this does not work. Does anyone have a solution?

NPE:

Exception in thread "AWT-EventQueue -0" java.lang.nullpointerexception
at Arkiv.getMorTre(Arkiv.java:209)
at Arkiv.getMorTre(Arkiv.java:211)
at Arkiv.getMorTre(Arkiv.java:211)
at MinRamme$4.actionPerformed(MinRamme.java:89) <37 internal calls>

Answer 1

Where does the NullPointerException occur? That would help… That being said:

Inside your else clause, your

if (id==0) {

is useless, since you’re testing that at the beginning and the id isn’t changed.

I think you need to check if

getMother(id) 

returns null, that is probably where you’re getting the NullPointer… but you could confirm that now, couldn’t you?