Про DataInputStream

[Nastya2018]

Про DataInputStream

Ребята как поменять код на DataInputStream. Чтобы памяти хватило когда создаю матрицу и умножаю миллион на миллион

   public static void writeMatrixToFile(Matrix m, String filename) {

        try(FileWriter writer = new FileWriter(filename, false)){
            String strForWrite = "";
            
            writer.write(String.valueOf(m.getRowCount()));
            writer.write("\n");
            writer.write(String.valueOf(m.getColCount()));
            writer.write("\n");

            for (int i = 1; i <= m.getRowCount(); i++){
                for (int j = 1; j <= m.getColCount(); j++){
                    
                    strForWrite += m.get(i,j) + " ";
                }
                strForWrite += "\n";
            }

            writer.write(strForWrite);
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } catch(MatrixIndexException e) {
             e.printStackTrace();
        }
    }

    public static Matrix loadMatrixFromFile(String filename) {

        try(FileReader reader = new FileReader(filename)) {
            String strFromFile = "";

             
            while (reader.ready()) {
                strFromFile += (char) reader.read();
            }

            String[] arr = strFromFile.split(" |\n");
            Matrix result = new Matrix1D(Integer.valueOf(arr[0]), Integer.valueOf(arr[1]));

            int row = 1;
            int col = 1;

            for (int i = 2; i < arr.length; i++){
                if (!arr[i].equals("")){
                    result.put(row, col, Integer.valueOf(arr[i]));
                    col++;
                    if (col == result.getColCount() + 1){
                        col = 1;
                        row++;
                    }
                }
            }

            return result;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}