我们可以按Map中的键和值对Set进行排序吗？

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 need to sort the cars by their order in race:

public class Race {
private Set<Car> cars = new TreeSet<>();
private Map<Integer, Integer> races = new TreeMap<>();//key represents the order in race, value represents the ID of a car, so i need to sort cars by the keys in races
...
public Collection getSortedCars() { ??? }
}

-any ideas how to get sorted cars? thanks much

EDIT: Im sorry, i used very bad example with values, so heres it with identifiers, i hope you get what i need..

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 (eg 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));