Sorting java arrayList with predefined order

Question

I have an unsorted list but I want to sort in a custom way i.e.

item_one_primary.pls
item_one_secondary.pls
item_one_last.pls

item_two_last.pls
item_two_primary.pls
item_two_secondary.pls

item_three_secondary.pls
item_three_last.pls
item_three_primary.pls

Here is my predefined order : primary, secondary, last

Above unordered list once the ordering is applied should look like this :

item_one_primary.pls
item_one_secondary.pls
item_one_last.pls

item_two_primary.pls
item_two_secondary.pls
item_two_last.pls

item_three_primary.pls
item_three_secondary.pls
item_three_last.pls

I tried something with comparator but I end up something like this :

item_one_primary.pls
item_two_primary.pls
item_three_primary.pls

...

Does anyone have an idea how to get this sorted?

Here is some code I've used :

List<String> predefinedOrder;

public MyComparator(String[] predefinedOrder) {
        this.predefinedOrder = Arrays.asList(predefinedOrder);
    }

@Override
    public int compare(String item1, String item2) {
        return predefinedOrder.indexOf(item1) - predefinedOrder.indexOf(item2);
    }   

I didn't include the splits(first split by dot(.) second split by underscore(_) to get the item in pre-ordered list).

Answer 1

You have to use a Comparator that checks first the item number and only if they are equal, check your predefined order.

Try something like this:

public int compare(Object o1, Object o2) {
        String s1 = (String) o1;
        String s2 = (String) o2;

        String[] a1 = s1.split("_");
        String[] a2 = s2.split("_");

         /* If the primary elements of order are equal the result is 
         the order of the second elements of order */ 
        if (a1[1].compareTo(a2[1]) == 0) { 
            return a1[2].compareTo(a2[2]); 
        /* If they are not equal, we just order by the primary elements */
        } else {
            return a1[1].compareTo(a2[1]);
        }
    }

This is just a basic example, some extra error checking would be nice.