CODEWITHSUNDEEP
javafor-loopmatrixruntime-errormultidimensional-array
dev leb
dev leb

Reputation: 29

what is the error in my code ? trying to buid 2D matrix

i am creating a program that create a 2D matrix using java it suppose to build a 2D array after it check if the numbers are prime or no.

i know that the error is in the for loop of the createMatrix Function and i hope that someone can help me and explain where is my error and how to fix it.

the system display this error :

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2
    at test6.test6.createMatrix(Question6.java:26)
    at test6.test6.main(Question6.java:52)

and this is my code :

package test6;

public class test6 {

    public static int isPrimeNumber(int number) {
        if (number == 2 || number == 3) {
            return 1;
        }
        if (number % 2 == 0) {
            return 0;
        }
        int sqrt = (int) Math.sqrt(number) + 1;
        for (int i = 3; i < sqrt; i += 2) {
            if (number % i == 0) {
                return 0;
            }
        }
        return 1;
    }

    public static int[][] createMatrix(int[][] m) {
        int i, j;
        for (i = 0; i < m[0].length; i++) {

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

        }
        return m;

    }

    public static String toString(int[][] m) {
        StringBuilder text = new StringBuilder();
        for (int row = 0; row < m.length; row++) {
            int r[] = m[row];
            for (int col = 0; col < r.length; col++) {
                if (col > 0)
                    text.append(", ");
                text.append(r[col]);
            }
            text.append("\n");
        }
        return text.toString();
    }

    public static void main(String[] args) {

        int[][] num = new int[][] { { 1, 2, 3, 4 }, { 5, 6, 7, 8 } };

        System.out.println(toString(createMatrix(num)));
    }

}

Upvotes: 0

Views: 67

Answers (2)

Edwin Buck
Edwin Buck

Reputation: 70959

You are transversing your m X n array n times down the m direction and m times down the n direction.

As a result, within createMatrix(...) you run a good chance of walking out of the array (unless it is a square array). Also, createMatrix is a horrible name for something that just prints out a matrix created elsewhere.

Upvotes: 1

aioobe
aioobe

Reputation: 421280

You've swapped the indexes the other way around:

for (i = 0; i < m[0].length; i++) {    // i runs over the columns of first row
    for (j = 0; j < m.length; j++) {   // j runs over the rows
        System.out.println(m[i][j]);   // here i is the row, and j is the column!
    }
}

A better way to loop over the matrix is:

for (i = 0; i < m.length; i++) {        // let i run over the rows
    for (j = 0; j < m[i].length; j++) { // let j run over the columns
        System.out.println(m[i][j]);
    }
}

Upvotes: 4

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