Slides from a short presentation I gave at ClassPass introducing a select few new features in Java 8.

1. Java 8
An Introduction by
Jason Swartz

2. Agenda
1. Lambda Expressions
2. Streaming Collections
3. Monadic Collections

3. 1. Lambda Expressions

4. Math Function
f(x) = x * x

5. Java Function
int sqr(int x) { return x * x; }

6. Anonymous Function
x -> x * x

7. Java Anonymous Function
x -> x * x

8. Java Anonymous Function
(x) -> x * x

9. Java Anonymous Function
(x, y) -> x + y

10. Java Anonymous Function
() -> 42

11. Java Anonymous Function
f = x -> x * x;
int y = f.apply(5);

12. Java Anonymous Function
f = (x, y) -> x + y;
int y = f.applyAsInt(5, 7);

13. Java Anonymous Function
r = () -> {
System.out.println("Hello");
};
r.run();

14. Java Method Reference
c = System.out::println;
c.accept("Hello");

15. Now You Know Lambdas

16. 2. Streaming Collections

17. Doubling Items In A List
List<Integer> nums = Arrays
.asList(1, 2, 3);
int sqr(int x) { return x * x; }

18. Doubling Items In A List
nums2 = new ArrayList<Integer>();
for (int i : nums) {
nums2.add(sqr(i));
}

19. Doubling Items In A List
nums.stream()

20. Doubling Items In A List
nums.stream()
.map(this::sqr)

21. Doubling Items In A List
nums = nums.stream()
.map(this::sqr)
.collect(Collectors.toList());

22. Doubling Items In A List
nums = nums.stream()
.map(x -> x * x)
.collect(Collectors.toList());

23. Doubling Items In A List
nums = nums.parallelStream()
.map(x -> x * x)
.collect(Collectors.toList());

24. Doubling Items In A List
nums = nums.clusterStream()
.map(x -> x * x)
.collect(Collectors.toList());

25. Doubling Items In A List
nums = nums.dataCenterStream()
.map(x -> x * x)
.collect(Collectors.toList());

26. Welcome to
Declarative
Programming

27. Mapping To A List of Lists
nums.stream()
.map(x -> Arrays.list(x, x * x))
.collect(Collectors.toList());

28. Flatmap That List
nums = nums.stream()
.flatMap(x -> Arrays.list(x, x * x))
.collect(Collectors.toList());

29. Filtering Items In A List
nums = nums.stream()
.filter(x -> x % 2 == 0)
.collect(Collectors.toList());

30. Reducing A List
sum = nums.stream()
.reduce((a,i) -> a + i)
.get();

31. In Summary
sum = nums.stream()
.map(x -> x * x)
.flatMap(x -> Arrays.list(x, x * x))
.filter(x -> x % 2 == 0)
.reduce((a,i) -> a + i)
.get();

32. map()
flatmap()
reduce()
filter()

33. Now You Know Streams

34. 3. Monadic Collections

35. Have you done this?
User u = getUser(“Fred”);
String name = u.getName();
Exception in thread "main" java.lang.
NullPointerException

36. Null values stink

37. Use Optional<T>, not null
Optional<User> u = getUser("Fred");
if (! u.isPresent()) return;
String name = u.get().name;

38. Use Optional<T>, not null
Optional<User> u = getUser("Fred");
Optional<String> name = u
.map(user -> user.name);

39. Another Example

40. Checking a user name
User u = getUser(“Fred”);
Boolean result = null;
if (u != null)
Result = checkName(u.getName());
else
Result = false;

41. Checking a user name
Optional<User> u = getUser("Fred");
Boolean result;
if (u.isPresent())
result = confirmName(u.get().name);
else
result = false;

42. Confirming a user name with map()
Boolean result = getUser("Fred")
.map(u -> u.name)
.map(this::confirmName)
.orElse(false);

43. Optional is just a monad, a
monoid in the category of
endofunctors.
What’s the problem?

44. Optional is just a monad, a
monoid in the category of
endofunctors.
What’s the problem?

45. Optional is a zero- or one-
sized collection that helps
you cleanly handle
missing values.

46. More Monadic
Collections?

47. CompletableFuture is a
zero- or one-sized
collection that helps you
cleanly handle future
values.

48. Javaslang’s Try is a zero-
or one-sized collection that
helps you cleanly handle
exception-thrown values.

49. Javaslang’s Lazy is a zero-
or one-sized collection that
helps you cleanly postpone
calculating values.

50. Now You Know
Monadic Collections

51. Thanks For Watching!