2D array in java gives java.lang.ArrayIndexOutOfBoundsException

Question

I am new to Java and i am using eclipse for its compilation. I have seen many forums but i am not able to get around this error. I am creating a program for my homework and this is a small section of that program which is giving weird error. Any help is appreciated.

Here is where i am getting error -> aTwoD[i][j] = 0; <- at Initialize2D.<init>(Initialize2D.java:19)

I am stuck on this for quite some time now. :-(

What is did ->

public class Initialize2D
{
    private int[][] aTwoD;

    public Initialize2D (int N)
    {   
        System.out.println("N = " +N);
        int counter = 0;
        aTwoD = new int[N][N];

        int i = 1;
        while( i <= N ) 
        {
            int j = 1;
            while( j <= N )
            {
                System.out.println("counter = " +counter);
                aTwoD[i][j] = 0;
                System.out.println("aTwoD["+i+"]["+j+"] = " + aTwoD[i][j]);
                j++;
                counter++;
            }
            i++;
        }  
    }

    public static void main( String[] args)
    {
        Initialize2D TwoDArray = new Initialize2D(2);
    }   
}

error i was getting -> N = 2 counter = 0 aTwoD[1][1] = 0 counter = 1 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2 at Initialize2D.<init>(Initialize2D.java:19) at Initialize2D.main(Initialize2D.java:30) — user3043882
– user3043882, Commented Feb 9, 2014 at 9:44

Jigar Joshi · Accepted Answer · 2014-02-09 09:46:26Z

6

index starts from 0 so <= would cause out of bound

answered Feb 9, 2014 at 9:46

Jigar Joshi

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6 Comments

user3043882 Over a year ago

thanks Jigar. This really makes me feel stupid. But what i was trying to do was create an 2D array from aTwoD[1][1] to aTwoD[2][2]. That is why i was using "<=" and N = 2. Is there a special way of doing that ?

Jigar Joshi Over a year ago

if you specifically want to access [2][2] then you need array to contain 3 elements in both dimensions, change argument so that it creates [3][3]

user3043882 Over a year ago

Got it JB Nizet. I am very new to programming and i didn't know that.

user3043882 Over a year ago

Thank you to all of you guys for helping out. I really appreciate it.

user3043882 Over a year ago

Finally, if anyone felt bad that i copied by subsequent question in everyone's response, i again ask for forgiveness. I didn't mean to hurt anyone. Thanks for telling me this thing.

|

JB Nizet · Accepted Answer · 2014-02-09 09:46:07Z

1

Array indices in Java start at 0, and end at length - 1. They don't start at 1 and end at length as your code assumes.

answered Feb 9, 2014 at 9:46

JB Nizet

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1 Comment

user3043882 Over a year ago

thanks Jigar. This really makes me feel stupid. But what i was trying to do was create an 2D array from aTwoD[1][1] to aTwoD[2][2]. That is why i was using "<=" and N = 2. Is there a special way of doing that ?

Ashot Karakhanyan · Accepted Answer · 2014-02-09 09:46:16Z

1

change

while( j <= N )

to

while( j < N )

In java indexing of N size array goes from 0 to N-1 including.

answered Feb 9, 2014 at 9:46

Ashot Karakhanyan

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2 Comments

user3043882 Over a year ago

thanks Jigar. This really makes me feel stupid. But what i was trying to do was create an 2D array from aTwoD[1][1] to aTwoD[2][2]. That is why i was using "<=" and N = 2. Is there a special way of doing that ?

Ashot Karakhanyan Over a year ago

@user3043882, if your 2d array has only one element, you declare it aTwoD[1][1] and access as aTwoD[0][0] (it is unique element).

tilois · Accepted Answer · 2014-02-09 09:47:40Z

0

Beware that you iterate over i and j with the condition i <= N, j <= N.

Arrays in Java are zero based, meaning that they range between: 0 ... N-1. If you access them with N that will be out of their range.

Change your iterator from i <= N to i < N (same for j). That should do the trick.

answered Feb 9, 2014 at 9:47

tilois

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1 Comment

user3043882 Over a year ago

thanks Jigar. This really makes me feel stupid. But what i was trying to do was create an 2D array from aTwoD[1][1] to aTwoD[2][2]. That is why i was using "<=" and N = 2. Is there a special way of doing that ?

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