CODEWITHSUNDEEP
javaandroid
Alex Bravo
Alex Bravo

Reputation: 1598

java.lang.NullPointerException encountered in an unexpected place

I'm perplexed about this question: Is there a situation in which the first line in the following three lines can produce java.lang.NullPointerException?

if (mJobs == null || mJobs.size() == 0) { <-- trace shows exception here
    return null;
}

This exception is seen on an unrooted Android 4.4.4 phone. mJobs is declared like this:

ArrayList<Job> mJobs;

Any ideas would be highly appreciated.

Update: This crash happened one time out many thousands of runs.

Upvotes: 0

Views: 215

Answers (5)

riddle_me_this
riddle_me_this

Reputation: 9155

No, assuming you are using java.util.ArrayList and not your own implementation.

It would be clearer to use isEmpty() instead of size() == 0. I would also check to see how this code is getting called since you are returning null in either of those two cases.

Upvotes: 1

mikeb
mikeb

Reputation: 11287

Edited to say that the java "short-circuit" evaluation should never cause mJobs.size() to be evaluated, you might try it anyway to see if this is where it fails.

if (mJobs == null) {
    return null;
}
if (mJobs.size() == 0) { <-- trace shows exception here
    return null;
}

Upvotes: 0

Auric Mason
Auric Mason

Reputation: 26

The problem is the or of course, or means what it says, so the run time is evaluating both sides of the or for true before moving on. Short circuit does not occur in an or evaluation, so you can combine them in a single evaluation with short circuit if you use a ternary operation. Works the same as splitting them out, just shorter. 

if (mJobs == null ? true : mJobs.size() == 0) { 
    return null;
}

Upvotes: 0

Troy
Troy

Reputation: 166

I do not think that there is any way that your NullPointerException is coming from that first line of code. I bet you are running code that was compiled from a different version of the source code that you are looking at leaving you to believe that the error is on a different line than it really is. I would recompile your current code and then run it fresh.

Upvotes: 3

Martin
Martin

Reputation: 481

If mJobs is null then there is the possibility to throw the null pointer exception in mjobs.size()

if (mJobs == null || (mJobs !=null && mJobs.size() == 0)) { 
    return null;
}

Upvotes: 0

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