BufferedWriter/Reader Example

static void readFromFile() {
        File fileOfRecords = new File(PATH);
        String buff;
        String surname;
        String age;
        String sex;
        String city;
        String diagnosis;
        try (BufferedReader reader = new BufferedReader(new FileReader(fileOfRecords))) {
            if (fileOfRecords.length() != 0 && !(buff = reader.readLine()).equals("")) {
                int amount = Integer.parseInt(buff);
                int i = 0;
                boolean isCorrectData = true;
                while (isCorrectData && i < amount) {
                    surname = reader.readLine();
                    age = reader.readLine();
                    sex = reader.readLine();
                    city = reader.readLine();
                    diagnosis = reader.readLine();
                    isCorrectData = checkData(surname, age, sex, city, diagnosis);
                    if (isCorrectData) {
                        Patient patient = new Patient(surname, age, sex, city, diagnosis);
                        listOfPatients.add(patient);
                        i++;
                    }else {
                        System.out.println("(Incorrect data in the file. A new file will be created automatically.)");
                        listOfPatients.clear();
                    }
                }
            }
        } catch (FileNotFoundException e) {
            System.out.println("(No patient information found.)");
        } catch (IOException e) {
            System.out.println("(The file is open read-only.)");
        }
    }

    static void saveToFile() {
        File fileOfRecords = new File(PATH);
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(fileOfRecords))) {
            writer.append(String.valueOf(listOfPatients.size())).append("\n");
            for (Patient Patient : listOfPatients) {
                writer.append(Patient.getSurname()).append("\n");
                writer.append(Patient.getAge()).append("\n");
                writer.append(Patient.getSex()).append("\n");
                writer.append(Patient.getCity()).append("\n");
                writer.append(Patient.getDiagnosis()).append("\n");
            }
        } catch (IOException e) {
            System.err.println("Input/output error!");
        }
    }