How do I swap columns with a specific indexes in java 2d arrays?

Question

So I've been trying to solve following problem:

Given a two-dimensional array (matrix) and the two numbers: i and j. Swap the columns with indexes i and j within the matrix.

Input contains matrix dimensions n and m, not exceeding 100, then the elements of the matrix, then the indexes i and j.

Sample Input 1:

• 3 4
• 11 12 13 14
• 21 22 23 24
• 31 32 33 34
• 0 1

Sample Output 1:

• 12 11 13 14
• 22 21 23 24
• 32 31 33 34

In order to solve it, I wrote following code:

import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int rows = scanner.nextInt();
        int tables = scanner.nextInt();
        int[][] matrix = new int[rows][tables];

        int i = scanner.nextInt();
        int j = scanner.nextInt();

        for (int w = 0; w < rows; w++){
            int temp = matrix[w][i];
            matrix[w][i] = matrix[w][j];
            matrix[w][j] = temp;
        }

        System.out.print(matrix);
    }
}

And the error is Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 11 out of bounds for length 4 at Main.main(Main.java:15).

What might be the problem and solution to it?

Answer 1

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 11 out of bounds for length 4 at Main.main(Main.java:15).

Above error is because you are directly reading values into i and j but you forgot setting the values inside the matrix[][] as said by vince and jim in the comments.

Use loop to set the values

  for(int k=0;k<rows;k++){
      for(int l=0;l<cols;l++){
             matrix[k][l]=scanner.nextInt();
      }   
   }

and then loop through rows to swap values

Here goes the code

Live: https://onlinegdb.com/rJJ-kMTUL

import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int rows = scanner.nextInt();
        int cols = scanner.nextInt();
        int[][] matrix = new int[rows][cols];
        for(int k=0;k<rows;k++){
         for(int l=0;l<cols;l++){
             matrix[k][l]=scanner.nextInt();
         }   
        }
        int i = scanner.nextInt();
        int j = scanner.nextInt();
        for(int k=0;k<rows;k++){
        int temp =  matrix[k][i];
        matrix[k][i] = matrix[k][j];
        matrix[k][j]=temp;      
        }
         for(int k=0;k<rows;k++){
         for(int l=0;l<cols;l++){
             System.out.print( matrix[k][l]+" ");
         }
         System.out.println();
        }
    }
}