java.lang.ArrayIndexOutOfBoundsException when filling 2d array with user input

Question

This is the code I have currentlly.

public static void testClosestToMean() {

    Scanner input = new Scanner(System.in);
    System.out.println("How many rows does your array have: ");
    int rows = input.nextInt();
    System.out.println("How many columns does your array have: ");
    int columns = input.nextInt();

    double[][] numbers = new double[rows][columns];


    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < columns; j++)
        {
            System.out.println("Enter a value for your array: ");
            double values = input.nextDouble();
            numbers[rows][columns] = values;
        }
    }
}

When I run my program I reach System.out.println("Enter a value for your array: "); however when I input a single number and press enter this error occurs:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException

I'm just generally stuck and would like guidance or even an explanation of why this error keeps occurring.

Possible duplicate of What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it? — Siguza
– Siguza, Commented Apr 8, 2017 at 21:14

Chris Gong · Accepted Answer · 2017-04-08 20:32:31Z

4

The indices of your 2D array run from 0 to row-1 for the rows and 0 to columns-1 for the columns. However, you'r trying to access numbers[rows][columns] which is known as an "off-by-one error" because your accessing indices that are each one more than the max possible index. If you want to fix this, then replace rows with i and columns with j like so,

for (int i = 0; i < rows; i++)
{
    for (int j = 0; j < columns; j++)
    {
        System.out.println("Enter a value for your array: ");
        double values = input.nextDouble();
        numbers[i][j] = values;
    }
}

This way, you're adding entries into your 2D array by filling each row starting from the first row (at index 0) until you reach the last row (at index i-1). And while you're filling each row, you start filling the columns one by one by starting at the first column (at index 0) until you reach the last column (at index j-1).

edited Apr 8, 2017 at 20:32

answered Apr 8, 2017 at 20:26

Chris Gong

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3 Comments

Jacob G. Over a year ago

My guess is that OP just made a typo that he didn't notice

Daniel Over a year ago

Thanks man that was my issue, problem staring me straight in the face but didn't even notice it, cheers.

Chris Gong Over a year ago

@Daniel No problem. If you found the answer helpful then don't forget to upvote or accept the answer. Good luck coding!

Ousmane D. · Accepted Answer · 2017-04-17 19:01:38Z

1

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException means you are exceeding the elements. Please be aware that 0 can also be an item in an array.

For example:

array[0] = "Hey";
array[1] = "Sup! wow... just wow";

If I did

system.out.println(array[2]);

It would print the error

But if i did

system.out.println(array[0], array[1]);

It would work.

edited Apr 17, 2017 at 19:01

Ousmane D.

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answered Apr 8, 2017 at 20:28

Ashland Simpson

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Comments

Ousmane D. · Accepted Answer · 2017-04-17 19:01:54Z

0

In your code here :

numbers[rows][columns] = values;

I believe you meant

numbers[i][j] = values;

Thanks

edited Apr 17, 2017 at 19:01

Ousmane D.

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answered Apr 8, 2017 at 20:30

jscriptor

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