example reducing.java

    Comparator<String> byLength = Comparator.comparing(String::length);
    Map<String, String> longestLastNameByCity
            = Arrays.asList(new Person("pack", "provo"), new Person("pack2", "provo"), new Person("pack", "oreM")).stream().collect(groupingBy(Person::getCity,
                reducing("", Person::getLastName, BinaryOperator.maxBy(byLength))));
    System.out.println(longestLastNameByCity);
  }

  public static class Person {
    String lastName;
    String City;
    public Person(String lastName, String City) {
      this.lastName = lastName;
      this.City = City;
    }

    public String getLastName() {
      return lastName;
    }

    public String getCity() {
      return City;
    }
  }

List<Integer> b = Arrays.asList(2,3,4);
java.util.stream.Stream<Integer> stream = b.stream();
Optional<Integer> maxy = b.stream().collect(Collectors.maxBy((b1, b2) -> 3));
//Optional<Integer> maxz = b.stream().collect(joining());  // string only
Optional<Integer> max = b.stream().max(Integer::compareTo);
Optional<Integer> max2 = b.stream().reduce(Integer::compareTo);
Integer max3 = b.stream().collect(reducing(0, Integer::compareTo));
List<Integer> collect = b.stream().collect(toList());

maxy.ifPresent(System.out::println);

//max.ifPresent(System.out::println);
b.stream().count();