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Null Pointer (a curious case)
I get a null pointer at:
n[Array.getLength(n)-1] = cur;
not an arrayIndexOutOfBounds, but a null pointer? I didn't think you get get a null pointer on assignment, because after all aren't you supposed to be able to assign any object a null?
EDIT: n is a non primitive type. It is actually an array of objects.
Related threads:
Re: Null Pointer (a curious case)
Is n itself null?
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Re: Null Pointer (a curious case)
It shouldn't be:
n=utilities.increment(n); for(Tile cur:t.nodes){ if(cur!=null){ n[Array.getLength(n)-1] = cur;
public static Tile[] increment(Tile[] k){ int i = 0; int len = k==null ? 1:Array.getLength(k)+1; Tile[] tmp = new Tile[len]; if(len==1)return tmp; for(Tile kk: k){ tmp[i] = kk; ++i; } return tmp; }
I actually preform a null check on cur for operations that occur later.
Additional info:
n is a local variable, but was passed as a parameter. So to my knowledge as soon as I reassigned n it lost its connection to the passed array.
Post Script: I do understand your question though, because if I am being pragmatic I can concede that the system doesn't lie. So the only option here is that n is null? I guess my question for this thread is: could there be any other way I would get a null pointer there besides the fact that n is null?
Last edited by KAJLogic; April 8th, 2014 at 09:47 AM.
Re: Null Pointer (a curious case)
Is the type for n explicitly an array, or is it just an object?
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Re: Null Pointer (a curious case)
What do you mean by explicitly an array?
Re: Null Pointer (a curious case)
Can you post an SSCCE that demonstrates exactly what you're doing?
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KAJLogic (April 8th, 2014)
Re: Null Pointer (a curious case)
May I ask first, is there any other way I could get a null pointer there? Or, do you need more of the code to know for sure? In my head I keep getting this nagging urge to just stop myself and realize that an assignment cannot get a null pointer; the only way is if the array is null (). Is this not true? (assuming n is a non-primitive type)
Re: Null Pointer (a curious case)
Another way is that Array isn't the class but a local variable that is null.
If you don't understand my answer, don't ignore it, ask a question.
Re: Null Pointer (a curious case)
There is a level of incursion, but I believe that as soon as I reassign n it is no longer referencing the argument. Norm, do you mean a local variable that wasn't initialized?
Re: Null Pointer (a curious case)
That is the most common cause of a NPE.variable that wasn't initialized
If you don't understand my answer, don't ignore it, ask a question.
KAJLogic (April 8th, 2014)
Re: Null Pointer (a curious case)
Like, is it declared as:Originally Posted by KAJLogic
Tile[] n;
or it is declared as:
Object n;
I ask because if it is the first one (explicitly an array), you could get the length by:
n.length;
Instead of:
Array.getLength(n);
NOTE: notice no parentheses at the end of n.length. It is a variable reference, not a method call.
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Re: Null Pointer (a curious case)
Yes aussie your right I guess I never really reviewed the array API very much. In any case I appreciate your help. I will delve into this with your suggestions.
Re: Null Pointer (a curious case)
I suggested this because if you use n.length; and still get the null pointer, it means two things:
1. the problem is independent from the Array class
2. n is null
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Re: Null Pointer (a curious case)
What are you suggesting that the Array class is inaccurate or flawed?
Re: Null Pointer (a curious case)
Without seeing a complete (small) program that compiles, executes and shows the problem, most of this discussion is pretty useless.
If you don't understand my answer, don't ignore it, ask a question.
Re: Null Pointer (a curious case)
No.
Yes.
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Re: Null Pointer (a curious case)
No, but perhaps that the getLength() method does something which, due to the way your array is set up or something, unexpectedly causes a null pointer to be thrown. The Array.getLength() method is a native method, so I don't have a clue what it actually does.
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Re: Null Pointer (a curious case)
Aussie using the length variable produces the same error.
}
Last edited by KAJLogic; April 8th, 2014 at 01:38 PM.
Re: Null Pointer (a curious case)
Well that means that n is null.
n is set by the utilities.increment() method. Unfortunately, it doesn't appear that the increment() method can return null. Are you 100% sure the line you are getting the null pointer at is correct?
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Re: Null Pointer (a curious case)
Yeah at the top of the exception it cites that line then it cites a stream larger than my command prompt buffers capabilities here:
nO = t.getOptimalNodes(n,utilities.invert(a));
Last edited by KAJLogic; April 8th, 2014 at 01:04 PM.
Re: Null Pointer (a curious case)
Can you provide the full stack trace?
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Re: Null Pointer (a curious case)
This will be trivial to debug as soon as you provide the SSCCE. Before that, this is all just guesswork.
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