Getting min value from a hashmap which stores a object as value

Question

I want to get the min value from the data in the HashMap for a certain value in a object and if possible without doing a for loop etc. To get that I have currently this:

HashMap<String, Country> biggestCountries = new HashMap<String, Country>();

As the HashMap. The data I want to compare is stored within the object country and is getable with:

country.getArea();

Untill now I have tried this to get the min value but I only got it to work when I replaced the object Country with a Integer:

Collections.min(biggestCountries.entrySet(), Map.Entry.comparingByValue()).getKey();

Does someone maybe know a good way to get this to work?

Answer 1

You can create a Comparator that sorts based on area and get the Entry from Map

Comparator<Map.Entry<String, Country>> comp = 
         Comparator.comparing((Entry<String, Country> entry)->entry.getValue().getArea());

Using Collections.min

Collections.min(biggestCountries.entrySet(),comp);

Using stream

Entry<String, Country> entry = biggestCountries.entrySet()
                                               .stream()
                                               .min(comp)
                                               .orElse(null);

If you want to get only the Country, using stream

Country minCountry = biggestCountries.values()
                        .stream()
                        .min(Comparator.comparing(Country::getArea))
                        .orElse(null);

or using Collections.min

Country minCountry = Collections.min(biggestCountries.values(),
                           Comparator.comparing(Country::getArea));