Given a square matrix, calculate the absolute difference between the sums of its diagonals.

absDiagonalSum.java

public static int diagonalDifference(List<List<Integer>> arr) {
    int primarySum = 0;
    int secondarySum = 0;

    for (int i = 0; i < arr.size(); i++) {
        primarySum += arr.get(i).get(j);
        secondarySum += arr.get(i).get(arr.size() - j - 1);
    }

    return Math.abs(primarySum - secondarySum);
}