MatrixCalculator.java

package com.matrix.calculator;

import java.io.*;
import java.util.Scanner;

public class Calculator {

    public static void main(String[] args) {
        // write your code here

        System.out.println("Please Enter nine digits separated by spaces to construct your matrix: ");
        Scanner scanner = new Scanner(System.in);


        //true because we want to append to what ever is in the file already
        var fileName = "matrix.txt";

        writeMatrixFile(scanner, fileName);
        readMatrixFile(fileName);

    }

    private static void writeMatrixFile(Scanner scanner, String fileName) {
        try (FileWriter writer = new FileWriter(fileName, true); BufferedWriter bufferedWriter = new BufferedWriter(writer)) {
            String[] user_input = scanner.nextLine().strip().split(" ");
            for (int i = 0; i < user_input.length; i++) {
                final int integer = Integer.valueOf(user_input[i].trim());
                if (i == 3 | i == 6 | i == 9) {
                    bufferedWriter.newLine();
                }
                bufferedWriter.write(integer + " ");
            }

        } catch (IOException ignored) {
        }
    }

    private static void readMatrixFile(String fileName) {

        int[][] user_input_ = new int[3][3];

        try (FileReader reader = new FileReader(fileName); BufferedReader bufferedReader = new BufferedReader(reader);
             FileWriter writer = new FileWriter(fileName, true); BufferedWriter bufferedWriter = new BufferedWriter(writer)) {

            String line;
            int i = 0;
            while ((line = bufferedReader.readLine()) != null && !line.isEmpty() && !line.isBlank()) {
                String[] lineSplit = line.strip().split(" ");
                for (int j = 0; j < lineSplit.length; j++) {
                    user_input_[i][j] = Integer.valueOf(lineSplit[j].trim());
                }
                i++;
            }


            int difference = (user_input_[0][0] * user_input_[1][1] * user_input_[2][2])
                    - (user_input_[0][2] * user_input_[1][1] * user_input_[2][0]);


            bufferedWriter.newLine();
            bufferedWriter.write("difference : " + difference + " ");
            bufferedWriter.newLine();


        } catch (IOException ignored) {
        }
    }
}