How to fix array index out of bound though I made sure that array index is smaller than the array size?

Question

I made a class named Matrix in which with the help of few methods I can take order of matrix and elements of the matrix as input from the user. When I run the code it asks me to enter the order of the matrix and then instead of asking me to input the elements of the matrix it gives an error "java.lang.ArrayIndexOutOfBoundsException". You can look at the code.

  import java.util.Scanner;

  public class Matrix {
      int mRow;
      int nColumn;

      Scanner input = new Scanner(System.in);

      void getInput() {
          System.out.println("Enter number of rows:");
          mRow = input.nextInt();
          System.out.println("Enter number of columns:");
          nColumn = input.nextInt();
      }

      int a[][] = new int[mRow][nColumn];

      void getElement() {
          System.out.println("Enter the elements of the matrix: ");
          for (int i = 0; i < mRow; i++) {
              for (int j = 0; j < nColumn; j++) {
                  a[i][j] = input.nextInt();
              }
          }
      }

      void showMatrix() {
          for (int i = 0; i < mRow; i++) {
              for (int j = 0; j < nColumn; j++) {
                  System.out.print(a[i][j] + " ");
              }
            System.out.println();
        }
    }
}

  [1]: https://i.stack.imgur.com/guyRk.png

score 0 · Answer 1 · answered Jan 18 '19 at 06:04

Make sure to update the array when you get input, ie.

void getInput() {
    System.out.println("Enter number of rows:");
    mRow = input.nextInt();
    System.out.println("Enter number of columns:");
    nColumn = input.nextInt();
    a = new int[mRow][nColumn]; // you need this line
}

score 0 · Answer 2 · answered Jan 18 '19 at 06:06

0

This code

int a[][] = new int[mRow][nColumn];

issuing done outside of any method. At the time that it is being done, the values of mRow and nColumn are zero

Move this code into a method, after getInput has returned

answered Jan 18 '19 at 06:06

Scary Wombat

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score 0 · Accepted Answer · answered Jan 18 '19 at 06:10

Your program should look like this.

public class Solution {
int mRow;
int nColumn;

Scanner input = new Scanner(System.in);
int a[][] ;
void getInput() {
    System.out.println("Enter number of rows:");
    mRow = input.nextInt();
    System.out.println("Enter number of columns:");
    nColumn = input.nextInt();
    a = new int[mRow][nColumn];
}



void getElement() {
    System.out.println("Enter the elements of the matrix: ");
    for (int i = 0; i < mRow; i++) {
        for (int j = 0; j < nColumn; j++) {
            int value = input.nextInt();
            a[i][j] = value;
        }
    }
}

void showMatrix() {
    for (int i = 0; i < mRow; i++) {
        for (int j = 0; j < nColumn; j++) {
            System.out.print(a[i][j] + " ");
        }
      System.out.println();
  }
  }

public static void main(String[] args){
    Solution solution = new Solution();
    solution.getInput();
    solution.getElement();
    solution.showMatrix();
}
}

you were keeping your array declaration outside any method so your array was looking like this a[] by changing above code it looks like this a[[0, 0]]

Yes. I would declare `input` locally to `getInput` though. – Maurice Perry Jan 18 '19 at 06:12 — Maurice Perry, Jan 18 '19 at 06:12

How to fix array index out of bound though I made sure that array index is smaller than the array size?

3 Answers3