### Question:
Genericity { public void up(final List<? extends Number> numbers) { LOG.info(CollectionHelper.toString(numbers)); numbers.add(null); final Number n = numbers.get(0); LOG.info("numbers.get(0): " + n); }  void wildcard(final List<?> list); void up(final List<? extends Number> numbers); void down(final List<? super String> list);  }### Answer:
@Test public void testUp() { sample.up(nums); final List<Long> ls = LongStream.range(10, 20).boxed().collect(Collectors.toList()); sample.up(ls); }