Java 8 Streams API

Gender.java

package com.company;

public enum Gender {
    MALE, FEMALE
}

Main.java

package com.company;

import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {
        List<Person> people = getPeople();

        // Filter
        List<Person> females = people.stream()
                .filter(person -> person.getGender().equals(Gender.FEMALE))
                .collect(Collectors.toList());

//        females.forEach(System.out::println);

        // Sort
        List<Person> sortByAgeAndGender = people.stream()
                .sorted(Comparator.comparing(Person::getAge)
                        .thenComparing(Person::getGender).reversed())
                .collect(Collectors.toList());

//        sortByAgeAndGender.forEach(System.out::println);

        // All matches
        boolean allPersonAgeGreaterThan8 = people.stream()
                .allMatch(person -> person.getAge() > 8);

//        System.out.println(allPersonAgeGreaterThan8);

        // Any matches
        boolean anyPersonAgeGreaterThan8 = people.stream()
                .anyMatch(person -> person.getAge() > 8);

//        System.out.println(anyPersonAgeGreaterThan8);

        // reduce
        Integer totalAges = people.stream()
                .map(Person::getAge)
                .reduce(0, Integer::sum);

//        System.out.println(totalAges);

        //None matches
        boolean noneMathAgeGreaterThan8 = people.stream()
                .noneMatch(person -> person.getAge() > 8);

//        System.out.println(noneMathAgeGreaterThan8);

        // Max
        people.stream()
                .max(Comparator.comparing(Person::getAge));
//                .ifPresent(System.out::println);

        // Min
        people.stream()
                .min(Comparator.comparing(Person::getAge));
//                .ifPresent(System.out::println);

        // Group
        Map<Gender, List<Person>> groupByGender = people.stream()
                .collect(Collectors.groupingBy(Person::getGender));

        /*groupByGender.forEach(((gender, people1) -> {
            System.out.println(gender);
            people1.forEach(System.out::println);
        }));*/

        // Optionals
        Optional<String> personWithMaxAge = people.stream()
                .filter(person -> person.getGender().equals(Gender.FEMALE))
                .max(Comparator.comparing(Person::getAge))
                .map(Person::getName);

//        personWithMaxAge.ifPresent(System.out::println);

    }

    private static List<Person> getPeople() {
        return List.of(
                new Person("Antonio", 20, Gender.MALE),
                new Person("Alina Smith", 33, Gender.FEMALE),
                new Person("Helen White", 57, Gender.FEMALE),
                new Person("Alex Boz", 14, Gender.MALE),
                new Person("Jamie Goa", 99, Gender.MALE),
                new Person("Anna Cook", 7, Gender.FEMALE),
                new Person("Zelda Brown", 120, Gender.FEMALE)
        );
    }

}

Person.java

package com.company;

public class Person {
    private final String name;
    private final Integer age;
    private final Gender gender;

    public Person(String name, Integer age, Gender gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;
    }

    public String getName() {
        return name;
    }

    public Integer getAge() {
        return age;
    }

    public Gender getGender() {
        return gender;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", gender=" + gender +
                '}';
    }
}