Whats new in Java 8

Transcript

1. Whats new in Java 8 Piotr Kafel
2. Topics • Lambdas • Method reference • Type inference • Streams • Default methods • CompletableFuture
3. Lambdas
4. Motivation public List<Person> filterPersonsOlderThan18(List<Person> persons) { List<Person> result = new ArrayList<>(); for (Person p : roster) { if (p.getAge() >= 18) { result.add(p); } } return result; }
5. Motivation public List<Person> filterPersons(List<Person> persons, PersonPredicate predicate) { List<Person> result = new ArrayList<>(); for (Person p : persons) { if (predicate.test(p)) { result.add(p); } } return result; }
6. Motivation filterPersons(persons, new PersonPredicate() { public boolean test(Person person) { return p.getAge() >= 18 && p.getAge() <= 25; } }); filterPersons(persons, p -> p.getAge() >= 18 && p.getAge() <= 25);
7. Syntax p -> p.getAge() >= 18 && p.getAge() <= 25 p -> { LOGGER.info("Checking - " + p); return p.getAge() >= 18 && p.getAge() <= 25; } (p1, p2) -> p1.getAge() < p2.getAge()
8. Lambdas vs Anonymous Inner Classes
9. Translation public class Lambda { Function<String, Integer> f = s -> Integer.parseInt(s); } static Integer lambda$1(String s) { return Integer.parseInt(s); }
10. Translation int offset = 100; Function<String, Integer> f = s -> Integer.parseInt(s) + offset; static Integer lambda$1(int offset, String s) { return Integer.parseInt(s) + offset; }
11. Interesting fact Won't compile ! ( Illegal forward reference ) public class Foo { private final Runnable runnable = () -> System.out.println("I think " + someThought); private final String someThought = "I love burgers !"; }
12. Method References
13. Example Arrays.sort(arrayOfPersons, (Person a, Person b) -> { return a.getBirthday().compareTo(b.getBirthday()); } );
14. Example public class Person { // a lot of code here public static int compareByAge(Person a, Person b) { return a.birthday.compareTo(b.birthday); } } Arrays.sort(arrayOfPersons, Person::compareByAge);
15. Reference types • Static methods • Instance method on particular object • Instance method of an arbitrary object of a particular type • Reference to a constructor
16. Type Inference
17. Java 6 static <T> T pick(T a1, T a2) { return a2; } Serializable s = pick("d", new ArrayList<String>());
18. Java 7 Map<String, List<String>> myMap = new HashMap<String, List<String>>(); Map<String, List<String>> myMap = new HashMap<>();
19. Java 8 processStringList(Collections.<String>emptyList()); processStringList(Collections.emptyList());
20. Interesting fact Intellij 13 problems with type inference observable.reduce(new ArrayList<UserData>(), (accu, usersData) -> { accu.addAll(usersData); return accu; });
21. Streams
22. “A sequence of elements from a source that supports aggregate operations”. from http://www.oracle.com/technetwork/articles/java/ma14-java-se-8-streams-2177646.html
23. Example List<Integer> transactionsIds = transactions.stream() .filter(t -> t.getType() == Transaction.GROCERY) .sorted(comparing(Transaction::getValue).reversed()) .map(Transaction::getId) .collect(toList());
24. Intermediate vs final methods Stateful vs stateless methods Streams cannot be reused Laziness IntStream, LongStream, DoubleStream etc.
25. Default Methods
26. How ? Iterable<String> iterable = new ArrayList<>(listFullOfStrings); iterable.forEach(System.out::println);
27. Example public interface Iterable<T> { // more code here default void forEach(Consumer<? super T> action) { Objects.requireNonNull(action); for (T t : this) { action.accept(t); } } }
28. Traits like in Scala, Groovy etc. ?
29. CompletableFuture
30. Example CompletableFuture<Merchant> merchantFuture = CompletableFuture.supplyAsync( () -> getMerchantForUser(id)); CompletableFuture.supplyAsync(() -> getUser(id)) .thenCombine(merchantFuture, (u, m) -> createTemplateData(u, m)) .thenAccept(templateData -> sendEmail(templateData));
31. CompletableFuture vs Observable
32. Thats all folks !