How to use Java Optional to elegantly replace Ternary operators

Question

A super simple question:

Here's my plain Java code using traditional ternary operator ?

public DateTime getCreatedAt() {
    return !recordA.isPresent() ? recordB.get().getCreatedAt() : recordA.get().getCreatedAt();
}

My best bet is following:

public DateTime getCreatedAt() {
    return recordA.map(
        record -> record.getCreatedAt())
        .orElse(recordB.get().getCreatedAt());
  }

This could compile, but looks like it's not behaving correctly. It always executes both branches, for e.g. when recordA isPresent(), it still executes recordB.get().getCreatedAt() which throws me

java.util.NoSuchElementException: No value present

Any help is appreciated!

Basically, I'd like to replace the traditional ternary operator with more advanced Optional/lamda features.

user_1424875 · Answer

To avoid eagerly evaluating else-branches, use orElseGet, which takes an instance of the functional interface Supplier:

return recordA.map(
    record -> record.getCreatedAt())
    .orElseGet(() -> recordB.get().getCreatedAt());

user_812787 · Answer

My question about recordB being Optional got unanswered but if it is Optional then you cannot just safely call its get method, you need to check if it is empty or not. Here safe call to get record or null if both recordA and recordB are empty Otionals.

        recordA
            .map(Record::getCreatedAt)
            .orElseGet( () -> recordB.map(Record::getCreatedAt).orElse(null) );

user_5862071 · Answer

You're looking for .orElseGet(() -> recordB.get().getCreatedAt()); and the reason to that can be found on this post --> Difference between Optional.orElse() and Optional.orElseGet()

Some people may find it a bit subjective but personally, I'd say by default, it makes more sense to use orElseGet() as opposed to orElse every time except in the case where the default object is already constructed as this will prevent many unexpected problems (given you didn't read the differences between orElse and orElseGet doc) as such of the one you're facing now.

read more from Java Optional – orElse() vs orElseGet()

Brad_Parks_26510 · Answer

If you are using Java 9+, you may be able to use ifPresentOrElse() method as more completely explained in this Stackoverflow answer.

recordA.ifPresentOrElse(
   value -> recordA.get().getCreatedAt(),
   () -> recordB.get().getCreatedAt()
);

How to use Java Optional to elegantly replace Ternary operators

4 Answers