Gatherers_B1.snippet

// Map Filter Gatherer
static <T, R> Gatherer<T, ?, R> mapFilter(
   Function<? super T, ? extends R> mapper,
   Predicate<? super R> filter) {

   return Gatherer.of(
      (_, element, downstream) -> {
         R mappedElement = mapper.apply(element);
         if (filter.test(mappedElement)) {
            return downstream.push(mappedElement);
         }
         return true;
      }
   );
}

var stream = Stream.of("one", "two", "three", "four", "five");
var result = stream
   .gather(mapFilter(String::length, length -> length > 3))
   .toList();
System.out.println("result = " + result);