OptionalExample.java

package com.kiroule.ocpupgradejava8.topic4_3;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.function.Predicate;

import static com.kiroule.ocpupgradejava8.topic4_3.Species.HUMAN;
import static com.kiroule.ocpupgradejava8.topic4_3.Species.MUTANT;
import static com.kiroule.ocpupgradejava8.topic4_3.Species.ROBOT;

/**
 * @author Igor Baiborodine
 */
public class OptionalExample {

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

    List<Optional<FuturamaCharacter>> characters = Arrays.asList(
        createOptional("Bender", "Rodriguez", ROBOT),
        createOptional("Philip", "Fry", HUMAN),
        createOptional("Turanga", "Leela", MUTANT),
        createOptional("John", "Zoidberg", null),
        Optional.empty());

    characters
        .forEach(c -> System.out.printf("%s, %s %n", getCharacterFullName(c), getSpeciesName(c)));

    System.out.printf("%nRobots: %n");
    characters.stream()
        .filter(new RobotSpeciesPredicate())
        .forEach(c -> System.out.printf("%s %n", getCharacterFullName(c)));
  }

  private static String getCharacterFullName(Optional<FuturamaCharacter> c) {
    return c.map(FuturamaCharacter::toString)
        .orElse("Empty FuturamaCharacter optional!");
  }

  private static String getSpeciesName(Optional<FuturamaCharacter> character) {
    return character.flatMap(FuturamaCharacter::getSpecies)
        .map(Species::name)
        .orElse("Possible alien species!");
  }

  private static Optional<FuturamaCharacter> createOptional(String firstName, String lastName,
                                                            Species species) {
    return Optional.of(new FuturamaCharacter(firstName, lastName, Optional.ofNullable(species)));
  }

  private static class RobotSpeciesPredicate implements Predicate<Optional<FuturamaCharacter>> {

    @Override
    public boolean test(Optional<FuturamaCharacter> character) {
      return character.isPresent()
             && character.get().getSpecies().isPresent()
             && ROBOT.equals(character.get().getSpecies().get());
    }
  }
}

enum Species {
  HUMAN, ROBOT, MUTANT
}

class FuturamaCharacter {

  private String firstName;
  private String lastName;
  private Optional<Species> species;

  public FuturamaCharacter(String firstName, String lastName, Optional<Species> species) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.species = species;
  }

  public Optional<Species> getSpecies() {
    return species;
  }

  @Override
  public String toString() {
    return firstName + " " + lastName;
  }
}