Sort ArrayList<String> by Date excluding the first half of the String

Question

I'm trying to sort a string which has this format:

Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:28/08/2019

This is the method I used to sort by the parameter Eta which is an Int:

Collections.sort(user_list, new Comparator<String>() {
            public int compare(String o1, String o2) {
                return Comparator.comparing(this::extractInt)
                        .thenComparing(Comparator.naturalOrder())
                        .compare(o1, o2);
            }
            private int extractInt(String s) {
                try {
                    return Integer.parseInt(s.split(":")[1].trim());
                } catch (NumberFormatException exception) {
                    return -1;
                }
            }
        });

How can I convert it to sort Date objects assuming that the Date parameter will never be null? I tried to make an extractDate method but then I don't know what to insert where there is Comparator.naturalOrder() .

Answer 1

You might want to do it this way:

// Creating some dummy data
List<String> userList = Arrays.asList("Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:28/08/2019",
        "Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:26/08/2019",
        "Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:30/08/2019",
        "Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:12/08/2019");

// Sorting based on LocalDate
userList.sort(Comparator.comparing(s -> {
    String stringDate = s.substring(s.lastIndexOf(':') + 1).trim();
    return LocalDate.parse(stringDate, DateTimeFormatter.ofPattern("dd/MM/yyyy"));
}));

// printing the lists
userList.forEach(System.out::println);

Sorted Result:

Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:12/08/2019
Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:26/08/2019
Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:28/08/2019
Test: XX    Genere: Maschio    Eta: YY    Protocollo: A    Date:30/08/2019