Having problems with the Stream API sorting and filtering

Question

I have a Citizen class which contains the reference class that I am utilizing. What I want to do is to pass the data that I read from a file into the Citizen class, store these data into an array or list and sort it using the stream api

Here's what I am working on currently

The readCSV method which reads the data.csv file, passes it in the reference class and adds it onto the List:

public static ArrayList<Citizen> readCSV(String datafile) throws FileNotFoundException {
    ArrayList<Citizen> citizenList = new ArrayList<>();
    String contents;
    BufferedReader brd = new BufferedReader(new FileReader(datafile));
    try {
        while ((contents = brd.readLine()) != null) {
            String[] st = contents.split(",(?=([^\\\"]*\\\"[^\\\"]*\\\")*[^\\\"]*$)");
            String firstName = st[1];
            String lastName = st[0];
            String email = st[2];
            String address = st[3];
            int age = Integer.parseInt(st[4]);
            boolean resident = false;
                if ((st[5].compareToIgnoreCase("Resident")  == 0)) {
                    resident = true;
                }
            int district = Integer.parseInt(st[6]);
            String gender = st[7];
                if (st[7].compareToIgnoreCase("Female") == 0) {
                    gender = "female";
                } else if (st[7].compareToIgnoreCase("Male") == 0) {
                    gender = "male";
                }

            citizenList.add(new Citizen(lastName, firstName, email, address, age, resident, district, gender));
        } // end of while loop
    } // end of try
    catch (Exception e) {
        System.out.println("File not found:" + e.getMessage());
    } // end of Catch
    return citizenList;
}// end of ReadFile method

And here's the method that is supposed to sort the data from the read file:

  public static List<Citizen> getName(List<Citizen> citizens, String path) throws FileNotFoundException {
    ArrayList<Citizen> list = readCSV(path);
    Citizen foundCitizen = new Citizen();

    list.stream().sorted(Comparator.comparing(Citizen::getLastName)).collect(Collectors.toList());

    return list;

Here's the print method that I call in the main method. This method will will inbvoke the getName method and print the sorted values:

public static void printName(List<Citizen> citizens, String path) throws FileNotFoundException {
    ArrayList<Citizen> shitizen = new ArrayList<>(getName(readCSV(path), path));
    for (Citizen e : shitizen) {
        System.out.println(e);
    }
}

The problem is when I try to run the program, it only prints out the values in the order that is same from the file read. It does not sort it. I am trying to find out what is the problem with the code and how to correct it so that the sorted method works. Your help will be hugely appreciated. Thank you!

Answer 1

A stream does not modify your existing list, it creates a new list when you call collect() . What you need to do is assign the result of this method to your list variable:

list = list.stream()
           .sorted(Comparator.comparing(Citizen::getLastName))
           .collect(Collectors.toList());

Or alternatively:

return list.stream()
           .sorted(Comparator.comparing(Citizen::getLastName))
           .collect(Collectors.toList());

Answer 2

You can also just sort your list in place, no need for streams:

list.sort(Comparator.comparing(Citizen::getLastName));