Can we sort a Set by keys and values in Map?

Question

i have a class Car representing name and IDs of cars:

public class Car {
String name;
int ID;
}

and another class representing races in which i

Answer 1

I would not do this with a SortedSet, even though a custom Comparator could be used. The reason is because the races could be modified and thus invalidate any structure inside the TreeSet making the behavior "unpredictable".

Instead, I would make getSortedCars first get a sequence (e.g. a List) from the Set, and then sort and return such a sequence.

The actual sorting is "trivial" with Collections.sort and a custom Comparator as this is really a "sort by" operation, for instance:

class CompareCarsByWins implements Comparator<Car> {
    Map<Car,Integer> wins;

    public CompareCarsByWins(Map<Car,Integer> wins) {
        this.wins = wins;
    }

    public int compareTo (Car a, Car b) {
        // Actual code should handle "not found" cars as appropriate
        int winsA = wins.get(a);
        int winsB = wins.get(b);
        if (winsA == winsB) {
            // Tie, uhm, let's .. choose by name
            return a.getName().compareTo(b.getName());
        } else {
            // Sort most wins first
            return winsB - winsA;
        }
    }
    // ..
}

// Usage:
List<Car> results = new ArrayList<Car>(cars);
Collections.sort(results, new CompareCarsByWins(races));