Whats new in Java 8 - Speaker Deck

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Whats new in Java 8 Piotr Kafel

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Topics ● Lambdas ● Method reference ● Type inference ● Streams ● Default methods ● CompletableFuture

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Lambdas

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Motivation public List filterPersonsOlderThan18(List persons) { List result = new ArrayList<>(); for (Person p : roster) { if (p.getAge() >= 18) { result.add(p); } } return result; }

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Motivation public List filterPersons(List persons, PersonPredicate predicate) { List result = new ArrayList<>(); for (Person p : persons) { if (predicate.test(p)) { result.add(p); } } return result; }

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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);

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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()

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Lambdas vs Anonymous Inner Classes

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Translation public class Lambda { Function f = s -> Integer.parseInt(s); } static Integer lambda$1(String s) { return Integer.parseInt(s); }

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Translation int offset = 100; Function f = s -> Integer.parseInt(s) + offset; static Integer lambda$1(int offset, String s) { return Integer.parseInt(s) + offset; }

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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 !"; }

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Method References

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Example Arrays.sort(arrayOfPersons, (Person a, Person b) -> { return a.getBirthday().compareTo(b.getBirthday()); } );

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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);

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Reference types ● Static methods ● Instance method on particular object ● Instance method of an arbitrary object of a particular type ● Reference to a constructor

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Type Inference

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Java 6 static T pick(T a1, T a2) { return a2; } Serializable s = pick("d", new ArrayList());

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Java 7 Map> myMap = new HashMap>(); Map> myMap = new HashMap<>();

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Java 8 processStringList(Collections.emptyList()); processStringList(Collections.emptyList());

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Interesting fact Intellij 13 problems with type inference observable.reduce(new ArrayList(), (accu, usersData) -> { accu.addAll(usersData); return accu; });

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Streams

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“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

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Example List transactionsIds = transactions.stream() .filter(t -> t.getType() == Transaction.GROCERY) .sorted(comparing(Transaction::getValue).reversed()) .map(Transaction::getId) .collect(toList());

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Intermediate vs final methods Stateful vs stateless methods Streams cannot be reused Laziness IntStream, LongStream, DoubleStream etc.

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Default Methods

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How ? Iterable iterable = new ArrayList<>(listFullOfStrings); iterable.forEach(System.out::println);

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Example public interface Iterable { // more code here default void forEach(Consumer action) { Objects.requireNonNull(action); for (T t : this) { action.accept(t); } } }

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Traits like in Scala, Groovy etc. ?

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CompletableFuture

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Example CompletableFuture merchantFuture = CompletableFuture.supplyAsync( () -> getMerchantForUser(id)); CompletableFuture.supplyAsync(() -> getUser(id)) .thenCombine(merchantFuture, (u, m) -> createTemplateData(u, m)) .thenAccept(templateData -> sendEmail(templateData));