How to add a matrix to an Excel file in Java?

Question

Java

Hello!
I am working on one project, purely for myself, for practice, the essence of the program is to solve a system of equations by Jordan transformations. That is, there is a matrix, it is processed a certain number of times, I want the matrix to be entered into Excel after each processing, each new matrix should be added below the previous one. But it turns out only to overwrite, as a result, only the last matrix in the file.

Workbook workbook = new HSSFWorkbook();
        Sheet sheet = workbook.createSheet("Жорданові перетворення");

        for (int i = 0; i < arr.length; i++) {
            Row row = sheet.createRow(i);
            for (int j = 0; j < arr[i].length; j++) {
                Cell cell = row.createCell(j);
                cell.setCellValue(arr[i][j]);
            }
        }

        workbook.write(new FileOutputStream("C:\\Users\\dimic\\Desktop\\Jordan.xls"));
        
        workbook.close();

Answer 1

1. Workbook needs to be created through WorkbookFactory, which will load an existing file
2. Take the first sheet, determine the number of rows in the sheet and add a new matrix