Problem while converting old-school if usage to Optional.ifPresent()

Question

I am facing a problem while converting old-school if usage to Optional.ifPresent. Here is the previous version of the code.

State state = State.OK;
final Optional<Person> checkExistingPerson = checkIt();

if(checkExistingPerson.isPresent()) {
    Person person = checkExistingPerson.get();

    if("blah".equals(person.getName())) {
        state = State.DUPLICATE;
    } else {
        state = State.RESTORED;
    }

    return Member(person.getId(), state);
}

return Member(null, state);

And here is the Optional.ifPresent usage

State state = State.OK;
final Optional<Person> checkExistingPerson = checkIt();

checkExistingPerson.ifPresent(person -> {

    if("blah".equals(person.getName())) {
        state = State.DUPLICATE;
    } else {
        state = State.NEW;
    }

    return Member(person.getId(), state);
});

return Member(null, state);

And also, here is the screenshot what IntelliJ forces me to change it.

What is the best approach to use Optional regarding to my problem? Thx all!

Answer 1

1. External variables inside lambdas need to be final.
2. ifPresent accepts a Consumer so it has no return value, therefore you can't use return Member(person.getId(), state); (also remember that you are inside a lambda, so return is not going to exit from your method, but from the lambda).

map instead accepts a Function which has a return value, so you could use it instead of ifPresent.

This is how you could refactor your code, by moving state inside the lambda and by using map and orElseGet:

return checkExistingPerson.map(person -> {
    State state;

    if("blah".equals(person.getName())) {
        state = State.DUPLICATE;
    } else {
        state = State.NEW;
    }

    return Member(person.getId(), state);
})
.orElseGet(() -> Member(null, State.OK));

Answer 2

You can't change the value of a local variable from within a lambda expression. Besides, ifPresent can't return a value, as its return type is void.

Instead, you should use Optional.map, which transform the object wrapped by Optional if it's present:

return checkExistingPerson
    .map(person -> new Member(
            person.getId(), 
            "blah".equals(person.getName()) ? State.DUPLICATE : State.RESTORED))
    .orElse(new Member(null, State.OK));