There's a revolution calling! Lambda expressions are coming in Java 8 but how can developers benefit? We'll go through a series of code examples, that show how to: Use the new lambda expressions feature Write more readable and faster collections processing code using the Streams API Build complex data processing systems with the new collector abstraction Use lambda expressions in your own code

1. Simplifying with Lambdas
Richard Warburton

3. What do you mean simple?
Streams
Collectors
Conclusion

4. Lambda Expressions are here in Java 8!

7. What can we simplify?

8. Writing

9. Reading

10. Change

11. Better Libraries through Code as Data

12. button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
System.out.println("button clicked");
}
});

13. button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
System.out.println("button clicked");
}
});

14. button.addActionListener(?);

15. button.addActionListener(event -> ?);

16. button.addActionListener(event ->
System.out.println("button clicked")
);

17. String name = getName();
Runnable runnable =
() -> System.out.println(“Hello “ + name);

18. FUNCTIONAL INTERFACES
Everything in Java has a type
Problem: Need a type to represent a method
Solution: Use interfaces with a single method

20. public interface ActionListener {
public void actionPerformed(ActionEvent event);
}

21. INFERENCE
button.addActionListener(event ->
System.out.println("button clicked")
);
public interface ActionListener {
public void actionPerformed(ActionEvent event);
}

22. What do you mean simple?
Streams
Collectors
Conclusion

23. STREAMS
Support automated data parallelism
Abstraction to build computation pipelines
Iterator with inversion of control

24. int count = 0;
for (Artist artist : artists) {
if (artist.isFrom("London")) {
count++;
}
}
EXTERNAL ITERATION

25. artists.stream()
.filter(artist -> artist.isFrom("London"))
.count();
INTERNAL ITERATION

27. List<String> collected =
Stream.of("a", "b", "hello")
.map(item -> item.toUpperCase())
.collect(toList());
assertEquals(
asList("A", "B", "HELLO"),
collected);

29. List<String> beginningWithNumbers =
Stream.of("a", "1abc", "abc1")
.filter(value -> isDigit(value.charAt(0)))
.collect(toList());
assertEquals(
asList("1abc"),
beginningWithNumbers);

31. int sum =
Stream.of(1, 2, 3, 4)
.reduce(0, (acc, x) -> acc + x);
assertEquals(10, sum);

32. Putting it Together
for a given an album, find the nationality of every band
playing on that album

33. Putting it Together
1. get all the artists for an album,
2. figure out which artists are bands,
3. find the nationalities of each band
4. put together a list of these values.

34. Putting it Together
Set<String> origins =
album.getMusicians()
.filter(artist -> artist.getName().startsWith("The"))
.map(artist -> artist.getNationality())
.collect(toSet());

35. Eager vs Lazy
Set<String> origins =
album.getMusicians()
.filter(artist -> artist.getName().startsWith("The"))
.map(artist -> artist.getNationality())
// What’s happened at this point?
.collect(toSet());

36. Parallelism
Parallelism no longer means a rewrite of your code
Streams support parallelism out of the box
call .parallelStream() instead of .stream()
Performs well in the right circumstances, but not a
panacea

37. What do you mean simple?
Streams
Collectors
Conclusion

38. Enter the Collector
Collection is mutable reduction
Generic API for building up final values
Already seen collect(toList())

39. import static java.util.stream.Collectors.*;
collect(toList());
collect(toSet());
collect(toCollection(
() -> new TreeSet<>()));

41. Map<Boolean, List<Artist>> bandsAndSolo =
artists.collect(partitioningBy(a -> a.isSolo()));

43. Map<Artist, List<Album>> albumsByArtist =
albums.collect(
groupingBy(alb -> alb.getMainMusician()));

44. Map<Artist, Long> albumsByArtist =
albums.collect(
groupingBy(alb -> alb.getMainMusician(),
counting()));

45. Recap of Collectors
Mutable Reduction
A custom collector is just implementing an interface
Can collect other values
min, max
average, sum
summary statistics
join together strings

46. What do you mean simple?
Streams
Collectors
Design Patterns
Conclusion

47. How did we simplify?

48. Behavioural abstraction
A method/class which is parameterized by
different behaviours.

49. High Order Functions
Functions which take other functions as
arguments or return functions.

50. Writing
Avoided repeating basic looping and
collections constructs.

51. Reading
Words like map or reduce provide
immediate understanding.

52. Changing
Applying the same techniques in your own
code reaps huge rewards.

54. Q & A
@richardwarburto
insightfullogic.com
tinyurl.com/java8lambdas