Java Optional why not an ifNotPresent method?

Question

I was wondering why on the Java8 API the Optional class have the method ifPresent(Consumer< T> consumer) and not the ifNotPresent(Runnable** consumer)?

What's the intent of the API? Isn't it to emulate the functional pattern matching?

** Java doesn't have a zero argument void functional interface...

It is because the computation should be side effect free, so if I need to execute something when the computation fail, in the case it doesn't fail I will do nothing with the result, but lose it...ok now it's clear, thank you! — rascio
– rascio, Commented Apr 2, 2015 at 23:25
.ifPresentOrElse is in the pipeline for jdk9: see mailing list discussion — Misha
– Misha, Commented Apr 2, 2015 at 23:44
Runnable is indeed the zero-arg void functional interface. And the second argument of the new JDK 9 Optional.ifPresentOrElse is Runnable. — Stuart Marks
– Stuart Marks, Commented Apr 3, 2015 at 2:06
I know about the Runnable but it was created for another scope, it's just a matter to make the intent of a function explicit :) cheers — rascio
– rascio, Commented Apr 3, 2015 at 23:00

Ortomala Lokni · Accepted Answer · 2017-03-01 20:07:08Z

10

As Misha said, this feature will come with jdk9 in the form of a ifPresentOrElse method.

/**
 * If a value is present, performs the given action with the value,
 * otherwise performs the given empty-based action.
 *
 * @param action the action to be performed, if a value is present
 * @param emptyAction the empty-based action to be performed, if no value is
 *        present
 * @throws NullPointerException if a value is present and the given action
 *         is {@code null}, or no value is present and the given empty-based
 *         action is {@code null}.
 * @since 9
 */
public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction) {
    if (value != null) {
        action.accept(value);
    } else {
        emptyAction.run();
    }
}

edited Mar 1, 2017 at 20:07

answered Aug 6, 2015 at 18:24

Ortomala Lokni

63.6k27 gold badges202 silver badges268 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Java Optional why not an ifNotPresent method?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related