使用用户输入填充2d数组时，java.lang.ArrayIndexOutOfBoundsException

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.

Answer 1

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 ).

Answer 2

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.

Answer 3

In your code here :

numbers[rows][columns] = values;

I believe you meant

numbers[i][j] = values;

Thanks