Arrays doubt - pls clarify

[Neha Monga]

Hello All,

Which of the commented lines will generate an exception at runtime?

class Z extends Object {

static int godSmack[];
int danzig[];

static void main(String args[]) {
System.out.println(godSmack); //line 1
System.out.println(godSmack[0]); //line 2
System.out.println(new Z().danzig); //line 3
}
}

Answer is 'line 2'.

Can someone pls explain why line 2 will generate an exception and why line 1 and lline 3 will not?

Thanks in advance!

[ahmed yehia]

Line 1 and line 3 are both Instance variables so they have the value of "null".
Line 2 you are trying to access an array element which doesnt exist so you got NullPointerException
[ May 22, 2007: Message edited by: Ahmed Yehia ]

[anil kumar]

Hi
-----------------------------------------------
static int godSmack[];
int danzig[];
--------------------------------------------
The above these statements are by default
static int godSmack[]=null;
int digzig[]=null;

if you print
System.out.println(godSmark)//prints null
because it contains null

System.out.println(godSmark[0]);//Exception

Because it is not pointing to any array in the heap,but you are trying to access the 0th element.

That's you are getting Exception.

Thanks

Anil Kumar

[Raghavan Muthu]

By default, when you print an array it will give its hashcode value. It holds good for any object until the toString() method is not overridden.

Since an array is an object and its not pointing to any object (rather, its pointing to nowhere - NULL), you will get *null* in the console (if through SOPs).

In case of second statement, you are trying to access the 0th element of an array through its reference variable which is currently pointing to a non-existing object. So you get an EXCEPTION

HtH.

[Nik Arora]

Line 2 you are trying to access an array element which doesnt exist so you got NullPointerException

Hi Ahmed,
It causes ArrayIndexOutOfBounds Exception not NullPointerException


Regards
Nikhil

[Abdul Mohsin]

posted Today 12:13 PM Profile for nik arora Edit/Delete Post Reply With Quote

quote: Line 2 you are trying to access an array element which doesnt exist so you got NullPointerException



Hi Ahmed,
It causes ArrayIndexOutOfBounds Exception not NullPointerException


Regards
Nikhil

Hi Nikhil,

It won't give ArrayIndexOutOfBounds because array object is null, it gives NullPointerException


Regards,

Abdul Mohsin

[Raghavan Muthu]

Yes. NullPointerExcpetion is for any object which is being accessed but does not exist in the Heap.

Here you are trying to access the array object through its reference but it does not have a valid entry in Heap. Means, its not pointing to any object in heap.

godSmack[0] is something like godSmack.get(0) only. Thats where you get the NullPointerExcpetion and NOT ArrayIndexOutOfBoundsException.

NullPointerException has a higher precedence than ArrayIndexOutOfBounds while dealing with Arrays.

HtH.