Sort a list of Comparables using multiple string fields in a custom order

Question

With this class:

public class MyClass implements Comparable<MyClass> {

    private String status;
    private String name;
    private String firstName;  

    @Override
    public int compareTo(MyClass o) {
        return 0;
    }

}

I'd like to sort a list of MyClass objects with this order:

Firstly, status = "open", then "working" then, "close"
Secondly, name = "toto", then "titi"
Finally, firstName = "tutu", "tata"

How can I do this with the Comparable interface ?

https://stackoverflow.com/questions/369512/how-to-compare-objects-by-multiple-fields I tried the third answer in this post assuming I'm not using java 8. My filters are not the same, I don't know how to check by "keys" — whySoSerious, Jun 29 '18 at 09:32
Are these the only available names? I.e. `toto`, `titi`, `tutu`, `tata`? If not, then what's the general rule for sorting? Anyway, here is how you can use the comparator: `List list = ...; Collections.sort(list);` — Tamas Rev, Jun 29 '18 at 09:38

score 0 · Answer 1 · answered Jun 29 '18 at 09:45

I would do this like so: first define a set of lists which define the order for each field:

private static List<String> statusOrder = Arrays.asList("open", "working", "close");
private static List<String> nameOrder = Arrays.asList("toto", "titi");
private static List<String> firstNameOrder = Arrays.asList("tutu", "tata");

Then use List.indexOf to get the position of the element in the list, and then simply subtract the results:

@Override
public int compareTo(MyClass o) {
    final int statusComp = statusOrder.indexOf(status) - statusOrder.indexOf(o.status);
    if (statusComp != 0) return statusComp;
    final int nameComp = nameOrder.indexOf(name) - nameOrder.indexOf(o.name);
    if (nameComp != 0) return nameComp;
    return firstNameOrder.indexOf(firstName) - firstNameOrder.indexOf(o.firstName);
}

The issue with this approach is that indexOf will return -1 if the element is not in the list. You would need to define the behaviour in the case where MyClass contains non-standard values (perhaps it will never happen).

@DidierL I thought the agreement was sarcastic? I don't see it as an exact duplicate. That question wants to sort multiple string fields alphabetically, this question wants to sort multiple string fields, each with a defined non-alphabetic order. I've tried to improve the question to make it a clearer non-dupe. — Michael, Jun 29 '18 at 09:53

Sort a list of Comparables using multiple string fields in a custom order

1 Answers1