Simplifying java with lambdas (short)
- 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"); } });
- 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
- 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.