2 dimensional array to string code java

Your code is basically OK, except you are putting a leading space at the start of every line. To clean them up before returning, add this line:

aString = aString.replaceAll("(?m)^ ", "");

This uses regex to delete (by replacing with a blank) all spaces at the start of lines. The regex flag (?m) makes ^ match the start of every line of the input (normally ^ matches only the start of input).

I can think of three possible issues.

1. The test code doesn't want to see the space that you are putting at the beginning of every line.
2. The test code is passing an array where some of the entries are null. Your code doesn't cope with this.
3. The test code is passing an array where the entries have different lengths. Your code doesn't cope with this either.

Until you post the test code, we can't see which one the problem is. But you could deal with all three by changing your loop to this.

for (row = 0; row < a.length; row++) {
    if (a[row] != null && a[row].length > 0) {
        aString = aString + a[row][0];

        for (column = 1; column < a[row].length; column++) {
            aString = aString + " " + a[row][column];
        }
    }
    aString = aString + "\n";
}

int[][] a = new int[][]{{1,2,3},{4,5,6},{7,8,9}};

public static String arrayToString(int[][] a) {

    String aString;     
    aString = "";
    int column;
    int row;

    for (row = 0; row < a.length; row++) {
        for (column = 0; column < a[0].length; column++ ) {
        aString = aString + " " + a[row][column];
        }
    aString = aString + "\n";
    }

    return aString;
}

Output:

1 2 3
4 5 6
7 8 9

If you skip this line aString = aString + "\n"; your output will look like this

1 2 3 4 5 6 7 8 9