Using Optional in Java

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1

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.

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3

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:

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4

I don’t know Java so can’t really comment, but just wanted to say thanks for sharing :smiley: I’m sure someone might find it useful one day perhaps finding the thread via search :nerd_face:

5

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 … ?

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: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:

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