Pattern matching in Java 8+

PatternMatching.java

import java.util.Optional;
import java.util.function.Function;
import java.util.function.Predicate;

import static java.util.Optional.empty;
import static java.util.Optional.of;

public class PatternMatchingExample {

    public static void main(String[] args) {
        PatternMatching<? super String, ?> pm =
            PatternMatching
                .when("world"::equals, x -> "Hello " + x)
                .orWhen("monde"::equals, x -> "Salut " + x);

        pm.matches("monde").ifPresent(System.out::println);
    }

    @FunctionalInterface
    interface PatternMatching<T, R> {

        static <T, R> PatternMatching<T, R> when(Predicate<T> predicate, Function<T, R> action) {
            return value -> predicate.test(value) ? of(action.apply(value)) : empty();
        }

        default PatternMatching<T, R> orWhen(final Predicate<T> predicate, final Function<T, R> action) {
            return value -> {
                final Optional<R> result = matches(value);

                if (result.isPresent()) {
                    return result;
                }
                return (predicate.test(value)) ?
                    of(action.apply(value)) : empty();
            };
        }

        Optional<R> matches(T value);
    }
}