size of two dimensional arrays with null value

[Madhu Mk]

Hello Ranchers,

Could any one please assist me in how to check whether a given two dimensional aray is empty or with value..

Eg: int[][] yearsArrData;

for this array which is possible 1) yearsArrData.length == 0
2) yearsArrData == null

Thanks in advance..
Regards,
MK

[Campbell Ritchie]

You are nearly there. If you get array.length == 0 then you know you have an array which does actually exist, but contains 0 elements.
If you have array == null as true then you have an array which doesn't exist (null). Be sure to check for null before you check 0 length, otherwise you might get a NullPointerException.

[Madhu Mk]

Hi Campbell

Do mean empty arry means no existence of array object or any array with no elements - please confirm my understanding.

So if I want to check any array to be empty, always it is mandatory that before checking its length I have to check for null value ?. DO there is no single option to check the same.

Cheers,
K Madhu

[Campbell Ritchie]

By "empty array" I meant one which is not null but contains no elements, ie array.length is 0, same as a zero-length array.

"Null" array means one which doesn't exist ie array == null returns true.

No, you can't check for null and length 0 in one step, but you can write

if(array != null && array.length > 0)
{
   something();
}//end if

It is not essential to check for null values, but your original post did suggest you might have null arrays; then you always want the null check first.

I hope that helps. CR

[Campbell Ritchie]

Originally posted by K Madhu:
int[][] yearsArrData;

Assuming this is a field, at this point imagine you have

yearsArrData = null;

Now, like any field which has been declared the variable points to null (or 0/false for primitive types). So yearsArrData == null returns true. System.out.println(yearsArrData.length); throws a NullPointerException.

/* Inside constructor */
yearsArrData = new int[0][0];

You now have a zero-length array which contains 0 number of zero-length int arrays. So NOW yearsArrData == null returns false. System.out.println(yearsArrData.length); prints 0.

[edit]Minor spelling correction[/edit]
[ February 06, 2008: Message edited by: Campbell Ritchie ]