### Question:
Functions { public static <T, U, R> Function<U, R> applyPartial( final BiFunction<? super T, ? super U, ? extends R> mapper, final T t) { return u -> mapper.apply(t, u); } private  Functions(); static Predicate<T> by(final Function<? super T, ? extends U> mapper,
            final Predicate<? super U> predicate); static Function<T, Stream<R>> filterMap(final Predicate<? super T> predicate,
            final Function<? super T, ? extends R> mapper); static Function<U, R> applyPartial(
            final BiFunction<? super T, ? super U, ? extends R> mapper, final T t);  }### Answer:
@Test void test_applyPartial() throws Exception { final Object[] os1 = Stream.of(1, 2, 3).map(a -> Integer.sum(a, 4)).toArray(); assertThat(os1).contains(5, 6, 7); final Object[] os2 = Stream.of(1, 2, 3).map(applyPartial(Integer::sum, 4)).toArray(); assertThat(os2).contains(5, 6, 7); }