Alphabetically order new entries in an ArrayList using the compareTo method

Question

I want to alphabetically order entries into an ArrayList directory called entries. I want as a new entry is added to the directory to be placed into an appropriate position in the ArrayList.

For example, if we have two entries already in the directory with surnames: "Beta" and "Cee" and we want to add a new entry that has surname: "Alpha", "Alpha" should be placed first.

My question is, How can I overwrite the compareTo method to compare the two strings (String "one", and the other String that is passed into the method-"surname") alphabetically?

private ArrayList<Entry> entries=new ArrayList<>();

public void addEntry(String surname, String initial, String number) {
    Entry entry=new Entry(surname,initial,number);

    if (surname == null || initial == null || number == null)
        throw new IllegalArgumentException("Please fill all the required fields, [surname,initials,number]");
    else {
        boolean flag = false;
        for (int x = 0; x < entries.size(); x++) {
            String one= entries.get(x).getSurname();

            if (one.compareTo(surname)>0) {
                entries.add(x,entry);
                flag = true;
                break;
            }
        }
        if (!flag) {
            entries.add(entry);
        }
    }
}

Answer 1

In my opinion ArrayList is not a right choice for this situation, you seem to add the new Entry in the "correct" position according to the compareTo method defined in the Entry class.

So ideally a TreeSet should be used which basically maintains the ordering of the elements based on the compareTo defined in the Entry class which is the "default ordering".

class Entry implements Comparable<Entry>{
    private String surname;
    private String initial;
    private String number;

    Entry(String surname, String initial, String number){
        this.surname = surname;
        this.number =number;
        this.initial = initial;
    }
    @Override
    public int compareTo(Entry entry){
        return this.surname.compareTo(entry.surname);
    }
}

And the addEntry method should be simply:

private Set<Entry> entries = new TreeSet<>();

public void addEntry(String surname, String initial, String number) {
        if (surname == null || initial == null || number == null)
            throw new IllegalArgumentException("Please fill all the required fields, [surname,initials,number]");
        else {
            Entry entry=new Entry(surname,initial,number);
            entries.add(entry);
        }
 }

And if you really need an List, you can simply wrap the TreeSet instance in the ArrayList constructor:

List<Entry> list = new ArrayList(entries);