无法填充以TreeSet作为参数的HashMap

Question

I have this Map:

Map<City, TreeSet<Individual>> cityIndividualMap = new HashMap<City, TreeSet<Individual>>();

I populate this Map using this function:

public void add(List<Individual> individuals){
    for (Individual individual : individuals){
        individualSortedSet.add(individual);

        for(City city:individual.getCities()){
            TreeSet<Individual> individualList;

            if (cityIndividualMap.containsKey(city))
                individualSet = cityIndividualMap.get(city);
            else
                individualSet = new TreeSet<Individual>( new FitnessComparator());

            individualSet.add(individual);
            cityIndividualMap.put(city, individualSet);
        }
    }
} 

This is my Comparator:

public class FitnessComparator implements Comparator<Individual> {
    @Override
    public int compare(Individual individual1, Individual individual2) {
        if (individual1.getFitness() == individual2.getFitness())
            return 0;
        return (individual1.getFitness() > individual2.getFitness())? 1 : -1;
    }
}

The individual class is just a data class.. so I wont copy it over here.

For some very odd reason the CityIndividualMaps value only takes one element! I have executed this on debug mode many times but cannot see why only one item can be added.. Please could you check it out?

Answer 1

You keep overwriting every city's individual list with a new one. Change:

TreeSet<Individual> individualList;

if (cityIndividualMap.containsKey(city))
    individualSet = cityIndividualMap.get(city);
else
    individualSet = new TreeSet<Individual>( new FitnessComparator());

individualSet.add(individual);
cityIndividualMap.put(city, individualSet);

To:

TreeSet<Individual> individualList = cityIndividualMap.get(city);

if (individualList == null)
{
    individualList = new TreeSet<Individual>( new FitnessComparator());
    cityIndividualMap.put(city, individualList);        
}
individualList.add(individual);

Answer 2

Weird, I ran your code and it sort of worked, with the following exceptions:

1. There seems to be a mixup between 'individualList' and 'individualSet'

2. The declaration of 'cityIndividualMap' is inconsistent (Treeset versus hashmap), I assumed it's a HashMap based on your usage of it

3. class "City" should have hashCode + equals, otherwise you can get find several keys with the same City