Efficient way to check if a getter will return null in Java before passing to Optional?

Question

I have a simple data class such as

@Data
@Builder
public class MyPerson implements Serializable {
    String name;
    String age; //Purposely keeping as String here
    String address;
}

After constructing the object, I want to construct an Immutable object using it with the following definition, where I know name will never be null, but age and address might:

@Value.Style(stagedBuilder = true)
@Value.Immutable
public interface MyImmutablePerson extends Serializable {
    String getName();
    Optional<Integer> getAge();
    Optional<String> getAddress();
}

The first person object is created, and now want to create this second Immutable object, where age and address could be null

MyImmutablePerson.builder()
    .name(myPerson.getName())
    .age(myPerson.getAge()) //Could be null!
    .address(myPerson.getAddress()) //Could be null!
    .build()

My thought it is that I could pass to another function to check and return an empty optional if it is null:

private Optional<Integer> checkNullAge(String age) {
    if (age.isNull()) {
        return Optional.empty()
    }
    
    return Optional.of(age);
}

In doing this, I have duplicate another class just for Strings, another class for Boolean,.... etc. which is super ineficient.

Is there a better way to do a null check and then return an empty optional?

Just use `builder().age(Optional.ofNullable(myPerson.getAge()))` etc — Bohemian, Apr 21 '23 at 22:36
hmm this returns an error `Cannot resolve method 'age(Optional)'`, and trying to cast it to an Optional says that it's an inconvertible type — mitriola, Apr 21 '23 at 22:42
Make MyImmutablePerson a class and add @Builder? Or make it a `record`? — Bohemian, Apr 21 '23 at 22:47

xerx593 · Accepted Answer · 2023-04-21T23:32:57.810

3

return Optional.ofNullable(age);!?;)

Returns an Optional describing the given value, if non-null, otherwise returns an empty Optional.

For "conversion" (String->Integer) @bro proposed Optional.map()!(thx!) Which...

If a value is present, returns an Optional describing (as if by ofNullable(T)) the result of applying the given mapping function to the value, otherwise returns an empty Optional.

So that we can finally:

private /*static*/ Optional<Integer> checkNullAge(String age) {
    // try {
    
    return Optional.ofNullable(age).map(Integer::valueOf);
    // } catch (NumberFormatException nfE) ...
}

edited Apr 21 '23 at 23:32

answered Apr 21 '23 at 22:02

xerx593

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Should be `==` actually >.< The best I've come up with is `private Optional checkNullAge(String age) { if (age == null) { return Optional.empty(); } return Optional.of(Integer.valueOf(age)); } ` To do the Integer conversion. – mitriola Apr 21 '23 at 22:29
In not null/any case you could also encounter "number format exception" ...but (maybe) better "overall" approach: make it (possibly) same data type, (technically)nullable, but with "validation"... – xerx593 Apr 21 '23 at 22:57
2

`Optional` also has a [`map()`](https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/Optional.html#map(java.util.function.Function)) method: `Optional.ofNullable(age).map(Integer::valueOf)` – user16320675 Apr 21 '23 at 23:13
@xerx593 just saw your revision. Thank you, this is it! – mitriola Apr 21 '23 at 23:24

Efficient way to check if a getter will return null in Java before passing to Optional?

1 Answers1