import java.util.*;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.stream.Collectors;

public class TestTry {

    public static void main(String[] args) {
        List<TempStat> stats = new ArrayList<TempStat>();
        stats.add(new TempStat("Minsk", 18, new Date(2020, 1, 20)));
        stats.add(new TempStat("Minsk", 19, new Date(2020, 1, 21)));
        stats.add(new TempStat("Minsk", 20, new Date(2020, 1, 22)));
        stats.add(new TempStat("New York", 8, new Date(2020, 1, 20)));
        stats.add(new TempStat("New York", 9, new Date(2020, 1, 21)));
        stats.add(new TempStat("New York", 10, new Date(2020, 1, 22)));
        stats.add(new TempStat("London", 20, new Date(2020, 1, 20)));
        stats.add(new TempStat("London", 19, new Date(2020, 1, 21)));
        stats.add(new TempStat("London", 18, new Date(2020, 1, 22)));

        Collection<TempStat> result = stats.stream().collect(Collectors.toMap(
                TempStat::getCity,
                Function.identity(),
                BinaryOperator.maxBy(Comparator.comparing(TempStat::getDate))))
                .values();

        result.stream()
                .forEach(System.out::println);
    }


    static class TempStat {
        String city;
        int value;
        Date date;

        public TempStat(String city, int value, Date date) {
            this.city = city;
            this.value = value;
            this.date = date;
        }

        public String getCity() {
            return city;
        }

        public Date getDate() {
            return date;
        }

        @Override
        public String toString() {
            return "TempStat{" +
                    "city='" + city + '\'' +
                    ", value=" + value +
                    ", date=" + date +
                    '}';
        }
    }
}