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...

Answer 1

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();
    }
}