JShell experimentations with Java 14 collectors from streams API

fun-with-collectors.jshell

// Inspired by Venkat Subramaniam's talk "LJC Virtual Meetup: Exploring Collectors", similar to this former one: https://www.youtube.com/watch?v=z1eaTv_FASg
// See javadoc for Collectors: https://docs.oracle.com/en/java/javase/14/docs/api/java.base/java/util/stream/Collectors.html
// Run me with Java 14 via 'jshell --enable-preview'

record Person(String name, int age) {}
var persons = List.of(
  new Person("Sarah", 14),
  new Person("Venkat", 30),
  new Person("Sarah", 65),
  new Person("Farid", 12));

import static java.util.stream.Collectors.*

// List all persons (mutable or not)
persons.stream()
  .collect(toList())  
persons.stream()
  .collect(toUnmodifiableList())

// Filter
persons.stream()
  .filter(p -> p.age() < 20)
  .collect(toList())

// Filter and map
persons.stream()
  .map(Person::age)
  .collect(toSet())

// Join
persons.stream()
  .map(Person::name)
  .collect(joining(", "))

// Group by
persons.stream()
  .collect(groupingBy(Person::age))

// Sum by
persons.stream()
  .collect(groupingBy(Person::name, summingInt(Person::age)))

// Partition by
persons.stream()
  .collect(partitioningBy(p -> p.age() < 18))

// Tee (merge collectors)
persons.stream()
  .collect(
    teeing(
      filtering(
      	person -> person.age() < 18,
	toList()),
      filtering(
      	person -> person.age() >= 65,
	toList()),
      (underage, retired) -> List.of(underage.size(), retired.size())))