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I'm solving a problem where I am given a 2D array. The problem is, it is possible for one of the two arrays not to exist in the given 2D array.

I figured I could do a simple length check or null check but neither of those work. I get an arrayIndexOutOfBounds exception either way.

String smartAssigning(String[][] information) {
int[] employee1 = new int[3];
int[] employee2 = new int[3];
String name1 = "";
String name2 = "";

if(information[1].length <= 0 || information[1] == null)
{ return information[0][0];}

Caused by: java.lang.ArrayIndexOutOfBoundsException: 1
at _runefvga.smartAssigning(file.java on line 7)
... 6 more

the first array at index 0 exists but the second array at index 1 does not exist. Is there another way to check for this?

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  • 3
    You should create an Employee class. Don't use so many parallel arrays/variables. Commented Aug 15, 2016 at 15:47
  • 1
    Your checking [1] but returning [0]? Commented Aug 15, 2016 at 15:48
  • 2
    (information[1].length <= 0 || information[1] == null)? So it's: dereference the possible null pointer first and then check, if it was null? Commented Aug 15, 2016 at 15:49
  • You aren't null checking the 2d array that comes in. You are returning information[0][0] without checking that information[0] is not null. You are also checking if information[1] is not null after checking its length...the null check should be first Commented Aug 15, 2016 at 15:51
  • That was just an example. I tried doing a null check by itself and before the length and got the same thing. information[0] in this particular case is not null. And the code is breaking on the conditional not on whats inside of the conditional. But I think Susannah gave me the answer I was looking for. Commented Aug 15, 2016 at 16:10

3 Answers 3

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information.length will return the number of arrays that are contained. information[n].length will return the length of the array at index n. When you check if(information[1].length <= 0 ... you're checking to see if there is a second array and what the length of that array is. If there isn't a second array, you will get an out of bounds.

Try:

for(String[] array : information) {
    //do something...
}
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A 2-dimensional array in Java is actually just an array of arrays. Thus you need to check both the length of the "outer" array (the array of arrays) and the "inner" arrays (the arrays of int in your case). Unfortunately from your code it is not clear what you want to do, so depending on your goal and what you know about your callers (e.g. can information itself be null) you may want to check some or all of the following:

information!=null
information.length
information[x]!=null
information[x].length
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You need to take in account the order in which this conditions are checked.

You wrote:

if(information[1].length <= 0 || information[1] == null)

So first information[1].length <= 0 is checked and only if this is false than information[1] == null is checked.

The second condition makes no sense, if information[1] == null than there is already an Exception thrown when evaluating information[1].length.

So you need to switch the order to:

if(information[1] == null || information[1].length <= 0)

The second array does not exists, so information[1] == null is true

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1 Comment

information[1]==null can still throw an IndexOutOfBoundsException, you need to check the array information!=null and information.length first.

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