Java Lang Null Pointer Exception, but I don't understand why?

Question

I get a Java Lang Null Pointer Exception at this code:

for (int i = 0; i<fragen.size(); i++)
    {
        for (int x = 0; x<dbfragen.size(); x++)
        {
            if(i == dbfragen.get(x).getFrageNR())
            {
                if(fragen.get(i).getTyp() == 1)
                {

It happens in the last if statement. I used the Log file: fragen.size() is 30 and it crashes at i = 1

this makes no sense to me :O

Please help ;)

It should tell you the exact line. dbfragen is null or the object returned by dbfragen.get(x) or fragen.get(i) should be null. — Alexis C.
– Alexis C., Commented Nov 9, 2013 at 11:14
try to print fragen.get(i) , then fragen.get(i).getTyp() before your if condition , see which one throws exception — Hussain Akhtar Wahid 'Ghouri'
– Hussain Akhtar Wahid 'Ghouri', Commented Nov 9, 2013 at 11:15
It tells me it's in line 49 (this is fragen.get(i).getTyp() ==1) But it works the first time, when i is 0, but not the second time, when it is 1 — Simon Tenbeitel
– Simon Tenbeitel, Commented Nov 9, 2013 at 11:16

Peter Lawrey · Accepted Answer · 2013-11-09 11:15:48Z

1

A collection can have 30 nulls in it. I suspect the first element is not null so it it fine but the second element index:1 is null.

BTW I suggest caching the lookup.

for (int i = 0; i<fragen.size(); i++) {
    MyType fragenI = fragen.get(i);
    if (fragenI == null) {
       // do something
       continue;
    }

answered Nov 9, 2013 at 11:15

Peter Lawrey

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1 Comment

Simon Tenbeitel Over a year ago

Thank you. You are right, there are 29 nulls in it. Now i have to find out why...

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