Get average age of male members

import java.time.LocalDate;

import java.time.chrono.IsoChronology;

import java.util.ArrayList;

import java.util.List;

import java.util.function.IntConsumer;

           public class Main

    public static void main(String[] args)

      List roster = createRoster();

      double average = roster

          .stream()

          .filter(p -> p.getGender() == Person.Sex.Male)

          .mapToInt(Person::getAge)

          .average()

          .getAsDouble();

    System.out.println("Average age of male members (bulk data operations):  " +average);

               public static List createRoster()

        List roster = new ArrayList<>();

        roster.add(

            new Person(

            "Fred",

            IsoChronology.Instance.date(1980, 6, 20),

            Person.Sex.Male,

            "fredexample.com"));

        roster.add(

            new Person(

            "Jane",

            IsoChronology.Instance.date(1990, 7, 15),

            Person.Sex.Female, "janeexample "));

        roster.add(

            new Person(

            "George",

            IsoChronology.Instance.date(1991, 8, 13),

            Person.Sex.Male, "georgeexample "));

        roster.add(

            new Person(

            "Bob",

            IsoChronology.Instance.date(2000, 9, 12),

            Person.Sex.Male, "bobexample "));

            return roster;

class Averager implements IntConsumer

    private int total = 0;

    private int count = 0;

    public double average()

        return count > 0 ? ((double) total)/count : 0;

    public void accept(int i) { total += i; count++; }

    public void combine(Averager other)

        total += other.total;

        count += other.count;

class Person

public enum Sex

      Male, Female

            String name;

  LocalDate birthday;

  Sex gender;

  String emailAddress;

            Person(String nameArg, LocalDate birthdayArg,Sex genderArg, String  emailArg)

      name = nameArg;

      birthday = birthdayArg;

      gender = genderArg;

      emailAddress = emailArg;

             public int getAge()

      return birthday

          .until(IsoChronology.Instance.dateNow())

          .getYears();

              public void printPerson()

    System.out.println(name + ", " + this.getAge());

    public Sex getGender()

      return gender;

    public String getName()

      return name;

    public String getEmailAddress()

      return emailAddress;

    public LocalDate getBirthday()

      return birthday;

    public static int compareByAge(Person a, Person b)

      return a.birthday.compareTo(b.birthday);

Check if there is any students from Milan

import java.util.Arrays;

import java.util.Comparator;

import java.util.List;

import java.util.stream.Collectors;

public class Main

  public static void main(String...args)

    Student raoul = new Student("Raoul", "Cambridge");

    Student mario = new Student("Mario","Milan");

    Student alan = new Student("Alan","Cambridge");

    Student brian = new Student("Brian","Cambridge");

    List transactions = Arrays.asList(

        new Graduate(brian, 2011, 300),

        new Graduate(raoul, 2012, 1000),

        new Graduate(raoul, 2011, 400),

        new Graduate(mario, 2012, 710),

        new Graduate(mario, 2012, 700),

        new Graduate(alan, 2012, 950)

);

    boolean milanBased =

        transactions.stream()

                    .anyMatch(transaction -> transaction.getTrader()

                                                        .getCity()

                                                        .equals("Milan")

);

    System.out.println(milanBased);

class Student

  private String name;

  private String city;

          public Student(String n, String c)

      this.name = n;

      this.city = c;

  public String getName()

      return this.name;

            public String getCity()

      return this.city;

            public void setCity(String newCity)

      this.city = newCity;

             public String toString()

      return "Student:"+this.name + " in " + this.city;

           class Graduate

            private Student trader;

  private int year;

  private int value;

            public Graduate(Student trader, int year, int value)

      this.trader = trader;

      this.year = year;

      this.value = value;

            public Student getTrader()

      return this.trader;

             public int getYear()

      return this.year;

              public int getValue()

      return this.value;

    public String toString()

      return "{" + this.trader + ", " +

             "year: "+this.year+", " +

             "value:" + this.value +"}";