Hands-on Java 8 with examples and open discussion about the more relevant new feature of Java 8: lambdas, streams, CompletableFeature, new Date & Time API.

1. Java 8
What’s new?
Onofrio Panzarino @onof80
JUG Marche - June 2014

2. Agenda
1. Lambda expressions
2. Stream API
3. Parallel operations
4. Default methods
5. Date time API
6. Optional: null is evil!
7. CompletableFuture

3. Lambda expressions
(lambda (x) (+ x 1)) LISP
function (x) { return x + 1; }; JavaScript
[](auto x) { return x + 1; }; C++11
(int x) => x + 1; C#
(_:Int) + 1 Scala
lambda x: x + 1 Python
x -> x + 1 Haskell

4. Java’s Lambdas
Syntax: (arguments) -> { body }
Collections.sort(employees,
(Employee p1, Employee p2) ->
p1.getSurname().compareTo(p2.getSurname()))
new Thread(() -> {
System.out.println("Thread started!");
}).start();

5. Stream API
On collections:
all.stream()
.filter(e -> e.getRole().equalsIgnoreCase(role))
.sorted(Comparator.comparing(e -> e.getBirthDate()))
.map(e -> e.getFullName())
.collect(Collectors.joining(separator));
On files:
Files.lines(Paths.get("myFile.txt"))
.map(String::trim)
.filter(s -> ! s.isEmpty()). // etc

6. Parallel Streams
Very difficult:
all.parallelStream()
.filter(e -> e.getRole().equalsIgnoreCase(role))
.sorted(Comparator.comparing(e -> e.getBirthDate()))
.map(e -> e.getFullName())
.forEach(System.out::println);

7. Default methods
public interface Person {
String getName();
String getSurname();
default String getFullName() {
return getSurname() + " " + getName();
}
}
Multiple inheritance ?
-> Must implement the method explicitly

8. New Dates API
● LocalDate, LocalTime and LocalDateTime
● ZonedDateTime
● Period vs Duration
● Chronologies
http://www.oracle.com/technetwork/articles/java
/jf14-date-time-2125367.html

9. Optional
.isPresent(); // (boolean)
.get();
.orElse(defaultValue);
.orElseGet( () -> new Employee(...) );
.orElseThrow( () -> new IllegalArgumentException() );
Functional:
.flatMap(e -> Optional.of(e.getAge()) ) ...
.filter(e -> e.getAge().getYears() > 50 ) ...
.map(e -> e.getAge() ) ...
.ifPresent(System.out::println);
.flatMap( e -> e.getItems().findFirst() );

10. CompletableFuture
CompletableFuture<String> future = CompletableFuture
.supplyAsync(() -> "Hello future!");
future.handle((msg, ex) -> {
if (ex != null) {
return "Houston! " + ex.getMessage();
} else {
return msg;
}
})
.thenAcceptAsync(a -> System.out.println(a));

11. CompletableFuture
Future composition!
CompletableFuture<Stream<String>> future1 = CompletableFuture
.supplyAsync(() -> repo1.getAll());
CompletableFuture<Stream<String>> future2 = CompletableFuture
.supplyAsync(() -> repo2.verySlowQuery());
future1
.thenCombineAsync(future2, Stream::concat)
.thenAccept(s -> {
System.out.print("Found: ");
s.forEach(System.out::println);
})
.join()

12. References
http://www.oracle.com/technetwork/java/javase/
8-whats-new-2157071.html
http://www.informit.com/articles/article.aspx?p=
2191426
Books: http://www.manning.com/urma/

13. Open Discussion
Thank you!
Onofrio Panzarino @onof80
JUG Marche - June 2014