Nested for loop 2D array initialization not working (java)

Question

i'm trying to simply create a method that returns a 2D array that has all the values entered based off a given pattern. Eclipse says that my code doesn't have any errors, yet when I go to run I get the response "[[I@2a139a55". I googled it and learned what it was about, yet I still don't know how to fix my code.

public class Transpose {

public static int[][] createPatterned2DArray(int row,int column){
    int width = column;
    int height = row;
    int[][] array = new int[height][width];

    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            array[i][j] = i + j + (width * i);
        }
    }

    return array;

}

public static void main(String[] args) {


    System.out.print(createPatterned2DArray(3,5));


}

}

the output is correct, as an `array` is an `Object`. Here it uses the default `Object` implementation of `toString`, which is printing the `type@hascode ` of the `Object`. You either want to iterate over it or use some api to print it directly. — SomeJavaGuy, Jun 01 '17 at 05:47

score 5 · Accepted Answer · edited Jun 01 '17 at 05:59

5

Try

System.out.println(Arrays.toString(array));

or if your array contains other arrays as elements

System.out.println(Arrays.deepToString(array))

edited Jun 01 '17 at 05:59

dumbPotato21

5,669
5
21
34

answered Jun 01 '17 at 05:58

pragadez

89
5

score 2 · Answer 2 · answered Jun 01 '17 at 05:53

You will have to print the 2d array.

For that you cannot simply do System.out.println()

The code should be somewhat like the following:

public class Transpose {

    public static int[][] createPatterned2DArray(int row,int column){
        int width = column;
        int height = row;
        int[][] array = new int[height][width];

        for (int i = 0; i < height; i++)
        {
            for (int j = 0; j < width; j++)
            {
                array[i][j] = i + j + (width * i);

            }
        }

        return array;

    }

    public static void main(String[] args) {


        int arr[][] = createPatterned2DArray(3,5);

        for (int i = 0; i < arr.length; i++){
            for(int j = 0; j < arr[i].length; j++){
                System.out.println(arr[i][j]);
            }
        }


    }

}

Oghli · Answer 3 · 2017-06-01T07:40:19.240

This System.out.print(array) statement won't give you the expected output of array elements values:

Actually you will get like this strange output when you print the array:

[[I@15db9742

The reason for this output:

An array is treated as an object, so the default outcome of Object#toString() will be used as string representation.

To achieve what you want:

Use Arrays.toString() method to print simple array or one-dimensional array.
Use Arrays.deepToString()method to print nested array.
Or you can use for loop traditional way to print the array.

In your case to print the 2D array you can just use:

System.out.print(Arrays.deepToString(createPatterned2DArray(3,5)));

Check this answer for more information.

Nested for loop 2D array initialization not working (java)

3 Answers3