Playing With Java Optional

Optional has been around since Java 8. And while I’ve heard of this magic box for some time, I’ve only recently explored it in-depth.

I stumbled upon the video Optional - The Mother of All Bikesheds by Stuart Marks and quite liked it. I’ll adapt some of Stuart’s snippets in this post to give a gentle introduction.

Okay, let’s write a method that gets an animal name by id. It’ll accept a list of animals and the id to search on. It should always returns a string: either the animal name, or unknown.

Sister Links #

• https://github.com/zwbetz-gh/playing-with-java-optional

Attempt 1 #

Imperative style with a trusty foreach loop.

private String getAnimalNameById(List<Animal> animals, Integer id) {
  for (Animal animal : animals) {
    if (animal.getId().equals(id)) {
      return animal.getName();
    }
  }

  return "unknown";
}

Attempt 2 #

Now we’re getting our feet wet with Optional. But the isPresent() check isn’t much better than a plain null check. Let’s improve it.

private String getAnimalNameById(List<Animal> animals, Integer id) {
  Optional<Animal> animal = animals
    .stream()
    .filter(a -> a.getId().equals(id))
    .findFirst();

  return animal.isPresent() ? animal.get().getName() : "unknown";
}

Attempt 3 #

Cool, now we’re using map() which will transform the value if it’s present. Then, we use orElse() which will return the value if present, otherwise it’ll return our fallback value. We can still improve it though.

private String getAnimalNameById(List<Animal> animals, Integer id) {
  Optional<Animal> animal = animals
    .stream()
    .filter(a -> a.getId().equals(id))
    .findFirst();

  return animal.map(Animal::getName).orElse("unknown");
}

Attempt 4 #

Nice, I like the way this reads. Now all of our work is done via method chaining.

private String getAnimalNameById(List<Animal> animals, Integer id) {
  return animals
    .stream()
    .filter(a -> a.getId().equals(id))
    .findFirst()
    .map(Animal::getName)
    .orElse("unknown");
}