Ordering with partial explicit and then another order?

Question

What I need is to order a list in a custom way, I\'m looking into the correct way and found guava\'s Ordering api but the thing is that the list I\'m ordering is not always goin

Answer 1

Here's a Comparator solution that uses a List of strings to represent your sorting order. Change your sorting order by merely changing the order of the strings in your sortOrder list.

  Comparator<AccountType> accountTypeComparator = (at1, at2) -> {
    List<String> sortOrder = Arrays.asList(
        "rrsp",
        "tfsa",
        "third"
        );
    int i1 = sortOrder.contains(at1.type) ? sortOrder.indexOf(at1.type) : sortOrder.size();
    int i2 = sortOrder.contains(at2.type) ? sortOrder.indexOf(at2.type) : sortOrder.size();
    return i1 - i2;
  };
  accountTypes.sort(accountTypeComparator);

Answer 2

You don't need Guava for this, everything you need is in the Collections API.

Assuming AccountType implements Comparable, you can just provide a Comparator that returns minimum values for "tfsa" and "rrsp", but leaves the rest of the sorting to AccountType's default comparator:

Comparator<AccountType> comparator = (o1, o2) -> {
    if(Objects.equals(o1.type, "rrsp")) return -1;
    else if(Objects.equals(o2.type, "rrsp")) return 1;
    else if(Objects.equals(o1.type, "tfsa")) return -1;
    else if(Objects.equals(o2.type, "tfsa")) return 1;
    else return o1.compareTo(o2);
};
accountTypes.sort(comparator);

If you don't want your other items sorted, just provide a default comparator that always returns 0.