Member.java

package java8.snippets.socialnet;

import java.util.Calendar;
import java.util.GregorianCalendar;

public class Member {
   
    public enum Sex {
        MALE, FEMALE
    }

    String name;
    Calendar birthday;
    Sex gender;
    String emailAddress;
  
    Member(String nameArg, Calendar birthdayArg,
        Sex genderArg, String emailArg) {
        name = nameArg;
        birthday = birthdayArg;
        gender = genderArg;
        emailAddress = emailArg;
    }  

    public int getAge() {
        Calendar today = GregorianCalendar.getInstance();
        int age = today.get(Calendar.YEAR) - birthday.get(Calendar.YEAR);
        if((birthday.get(Calendar.MONTH) > today.get(Calendar.MONTH))
            || (birthday.get(Calendar.MONTH) == today.get(Calendar.MONTH)
            && birthday.get(Calendar.DAY_OF_MONTH)
            > today.get(Calendar.DAY_OF_MONTH)))
        {
            age--;
        }
        return age;
    }

    public void printMember() {
       System.out.println(name + ", " + this.getAge());
    }
    
    public Sex getGender() {
       return gender;
    }
    
    public String getName() {
       return name;
    }
    
    
    public String getEmailAddress() {
       return emailAddress;
    }
}

Roster.java

package java8.snippets.socialnet;

import java.util.ArrayList;
import java.util.GregorianCalendar;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;

public class Roster {
    interface CheckMember {
        boolean test(Member p);
    }

    interface Block<T> {
        void apply(T a);
    }

    public static void printMembersOlderThan(List<Member> roster, int age) {
        for (Member p : roster) {
            if (p.getAge() >= age) {
                p.printMember();
            }
        }
    }

    public static void printMembersWithinAgeRange(
            List<Member> roster, int low, int high) {
        for (Member p : roster) {
            if (low <= p.getAge() && p.getAge() > high) {
                p.printMember();
            }
        }
    }

    public static void printMembers(
            List<Member> roster, CheckMember tester) {
        for (Member p : roster) {
            if (tester.test(p)) {
                p.printMember();
            }
        }
    }

    public static void processMembers(
            List<Member> roster,
            CheckMember tester,
            Block<Member> block) {
        for (Member p : roster) {
            if (tester.test(p)) {
                block.apply(p);
            }
        }
    }

    public static void processMembersWithMapper(
            List<Member> roster,
            Predicate<Member> tester,
            Function<Member,String> mapper,
            Consumer<String> block) {
        for (Member p : roster) {
            if (tester.test(p)) {
                String data = mapper.apply(p);
                block.accept(data);
            }
        }
    }

    public static <X,Y> void processElements(
            List<X> roster,
            Predicate<X> tester,
            Function<X,Y> mapper,
            Consumer<Y> block) {
        for (X x : roster) {
            if (tester.test(x)) {
                Y data = mapper.apply(x);
                block.accept(data);
            }
        }
    }

    public static void main(String... args) {

        List<Member> roster = new ArrayList<>();
        roster.add(
            new Member(
                "Fred",
                new GregorianCalendar(1980, 6, 20),
                Member.Sex.MALE,
                "fred@example.com"));
        roster.add(
            new Member(
                "Jane",
                new GregorianCalendar(1990, 7, 15),
                Member.Sex.FEMALE, "jane@example.com"));
        roster.add(
            new Member(
                "George",
                new GregorianCalendar(1991, 8, 13),
                Member.Sex.MALE, "george@example.com"));
        roster.add(
            new Member(
                "Bob",
                new GregorianCalendar(2000, 9, 12),
                Member.Sex.MALE, "bob@example.com"));

        for (Member p : roster) {
            p.printMember();
        }

        System.out.println("Members older than 20:");
        printMembersOlderThan(roster, 20);
        System.out.println();

        System.out.println("Members between the ages of 14 and 30:");
        printMembersWithinAgeRange(roster, 14, 30);
        System.out.println();

        printMembers(roster, new CheckMember() {
            @Override
            public boolean test(Member p) {
                return p.getGender() == Member.Sex.MALE
                        && p.getAge() > 20;
            }
        });

        processMembers(roster, new CheckMember() {
            @Override
            public boolean test(Member p) {
                return p.getGender() == Member.Sex.MALE;
            }
        }, new Block<Member>() {
            @Override
            public void apply(Member a) {
                a.printMember();
            }
        });

        System.out.println("############# Here!!! PLEASE");
        processMembersWithMapper(
            roster,
            m -> m.getGender() == Member.Sex.FEMALE,
            Member::getEmailAddress,
            System.out::println);

        processElements(
            roster,
            m -> m.getGender() == Member.Sex.FEMALE,
            m -> m.getEmailAddress(),
            email -> System.out.println(email)
        );

        roster.stream().parallel()
            .filter(m -> m.getGender() == Member.Sex.FEMALE)
            .map(Member::getEmailAddress)
            .forEach(System.out::println);
    }
}