finner

finner

Using Optional in Java

During a recent code review I came across this scenario:

Code in review

if (input.getValue() != null) {
   return Arrays.asList(value);
}  else {
   return input.getValues().stream().map(this::parseValues).collect(Collectors.toList())
}

And I suggested (in a compassionate way :grin: ) that we use Optional to treat the null value, so my suggestion was something like:

return Optional.ofNullable(input.getValue()).map(Arrays::asList)
       .orElseGet(input.getValues().stream().map(this::parseValues).collect(Collectors.toList()));

And I thought I was being very clever.

But then I realised it’s harder to understand the logic in this version. At least the if is a clear intent.
So I read up some more on Optional.
The Optional container allows us to perform logic including chaining map, flatMap, filter etc based on a value that may or may not be present. But this is not the real intention of Optional.

Optional is mainly used to represent attributes in an object that may be null or a method in an API that could return a null.

Consider a Person.
Everyone has a name, an age and a gender but may not have a car so we could define a class as follows:

class Person {
   private String name;
   private int age;
   private boolean female;
   private Optional<Car> car;
}

From this declaration it’s obvious that not everyone has a car and so the caller would then treat the car attribute appropriately.

My take away is the following:

Optional is not a replacement for occurrences if (x != null)

Any heavy users of Optional around?
Tips and/or suggestions would be very much appreciated.

Most Liked

finner

finner

Today I came across a very elegant use (IMHO) of Optional at work.
Consider the same person as above with a date of birth attribute:

public class Person {
   private String name;
   private String dob;

   // getters & setters etc etc (yep Java is verbose !!!!)
}

Now say you want to get that dob value into a Date object and do weird and wonderful date calculations.
You could use Optional like this:


// if you expect dob to be a string in the format yyyy-mm-dd
LocalDate birthday = Optional.ofNullable(persone.getDob())
    .map(LocalDate::parse)
    .orElse(null);  // or whatever

// or if the dob is in a different format, for example dd-MM-yyyy
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy");
LocalDate  d = Optional.ofNullable(p.getDob())
                .map(dob -> LocalDate.parse(dob, formatter))
                .orElse(null);

Now you have a LocalDate instance to play with.

In fact, once you have an Optional instance you have the following stream operators available

  • map
  • flatMap
  • filter

flatMap can be used to compose Optionals

public int ageDifference(Optional<Person> older, Optional<Person> younger) {
     return older.flatMap(o -> younger.map(y -> calAgeDifference(o.getDob(), y.getDob())); 
}

Quite cool :sunglasses:

Just thought I’d share :slight_smile:

finner

finner

cheers @AstonJ -
it’s actually good practice for me to help reinforce the learning by posting. Although at my age I will have forgotten it by end of week.
… so what were we talking about again … ?

AstonJ

AstonJ

:rofl: :rofl: :rofl:

I am just as bad - though I think a modern world is partly to blame - we are bombarded with information almost constantly now, imagine living a few thousand years ago before TV/Radio/Computers/Internet. Probably would have been quite serene and peaceful :smiley:

Funny thing is I read that article… and forgot most of it :rofl:

Popular Backend topics Top

DevotionGeo
I know that these benchmarks might not be the exact picture of real-world scenario, but still I expect a Rust web framework performing a ...
New
New
New
New
CommunityNews
The Magic of Python Context Managers. Recipes for using and creating awesome Python context managers, that will make your code more read...
New
First poster: bot
Rust 2021 Roadmap by Mark-Simulacrum · Pull Request #3037 · rust-lang/rfcs. The focus of this year is on project health, specifically as...
New
Jsdr3398
I love how elixir works and some of its perks, but I’m still pretty uncomfortable, especially when mix/hex gets involved. Did anyone els...
New
Exadra37
Finishing my app to take notes on Videos: I am aiming to put it online on my playground by this weekend. Edit: It’s up https://video...
New
mafinar
I’ll be participating. This would be very interesting because I have been having coders block + a lot of distraction this weekend. But l...
New
mafinar
We always have fun in this forum around this time of the year, discussing the days’ (or yesterdays’) challenges and talking through solut...
New

Other popular topics Top

siddhant3030
I’m thinking of buying a monitor that I can rotate to use as a vertical monitor? Also, I want to know if someone is using it for program...
New
PragmaticBookshelf
Design and develop sophisticated 2D games that are as much fun to make as they are to play. From particle effects and pathfinding to soci...
New
AstonJ
Seems like a lot of people caught it - just wondered whether any of you did? As far as I know I didn’t, but it wouldn’t surprise me if I...
New
mafinar
Crystal recently reached version 1. I had been following it for awhile but never got to really learn it. Most languages I picked up out o...
New
rustkas
Intensively researching Erlang books and additional resources on it, I have found that the topic of using Regular Expressions is either c...
New
AstonJ
We’ve talked about his book briefly here but it is quickly becoming obsolete - so he’s decided to create a series of 7 podcasts, the firs...
New
AstonJ
Was just curious to see if any were around, found this one: I got 51/100: Not sure if it was meant to buy I am sure at times the b...
New
New
PragmaticBookshelf
Author Spotlight: Tammy Coron @Paradox927 Gaming, and writing games in particular, is about passion, vision, experience, and immersio...
New
AstonJ
Curious what kind of results others are getting, I think actually prefer the 7B model to the 32B model, not only is it faster but the qua...
New