Harnessing the Power of Java 8 Streams
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Presented at the IndicThreads.com Software Development Conference 2016 held in Pune, India. More at http://www.IndicThreads.com and http://Pune16.IndicThreads.com --
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Harnessing the Power of Java 8 Streams
- 1. Harnessing the power of Java 8 Streams Praveer Gupta
- 2. Default Methods Lambda Expressions Streams Date-Time API CompletableFuture Optional
- 3. helps to make a strategic decision about what programming language should be adopted when starting to build a new software system Java 8 released on Mar 18, 2014
- 4. –Robert C. Martin “There are two parts to learning craftsmanship: knowledge and work. You must gain the knowledge of principles, patterns, practices, and heuristics that a craftsman knows, and you must also grind that knowledge into your fingers, eyes, and gut by working hard and practicing..”
- 5. Stream Intermediate Operators Terminal Operators Harnessing the power Java 8 Streams Programming Paradigm Concepts
- 6. Stream Collectorscollectreduce Intermediate Operators Terminal Operators computation creation Primitive Streams stateless/stateful Lazy & Short-Circuited Harnessing the power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts
- 7. Harnessing the power Java 8 Streams Declarative Programming Internal Iteration Programming Paradigm Concepts
- 8. Declarative SELECT NAME FROM PERSON WHERE AGE > 18; List<String> adults = group.stream() .filter(p -> p.age() > 18) .map(Person::name) .collect(toList()); You declare what the program has to do and the library takes care of how to do it
- 9. Declarative Focuses on What List<String> adults = new ArrayList<>(); for (Person person: group) if (person.age() > 18) adults.add(person.name()); Focuses on How and What vs Imperative List<String> adults = group.stream() .filter(p -> p.age() > 18) .map(Person::name) .collect(toList());
- 10. Old way vs New way final List<String> names = new ArrayList<>(); for (Person p : group) if (p.age() > 18) names.add(p.name()); return names; return group.stream() .filter(p -> p.age() > 18) .map(Person::name) .collect(toList()); List<String> namesOfAdultsInTheGroup(List<Person> group) { } External Iteration Internal Iteration new declarative way old imperative way List<String> namesOfAdultsInTheGroup(List<Person> group) { }
- 11. Application of Streams interface CustomerRepository { List<Customer> findByCity(String cityName); } API Definition
- 12. Application of Streams interface CustomerRepository { Stream<Customer> findByCity(String cityName); } try (Stream<String> stream = repository.findByCity(“Pune")) { return stream.filter(…).count(); } API Definition Usage of the API Consume items as they arrive Efficient memory usage
- 13. Stream computation creation Harnessing the power Java 8 Streams Declarative Programming Internal Iteration Programming Paradigm Concepts
- 14. Stream a read-only sequence of elements computational operations that will be performed in aggregate Collection efficient management of elements efficient access to elements
- 16. Stream Terminal Operator Operator1 Operator2 Operator3 Stream Pipeline List<String> namesOfAdultsInTheGroup(List<Person> group) { return } group.stream() .filter(p -> p.age() > 18) .map(Person::name) .collect(Collectors.toList());
- 17. names group Stream<Person> Archer (22 years) Barbara (17 years) Daisy (25 years) is person’s age > 18 ? Stream<Person> Stream<String> map to name of person collect into a list group.stream() .filter(p -> p.age() > 18) .map(Person::name) .collect( Collectors.toList()); Archer (22 years) Barbara (17 years) Daisy (25 years) Archer (22 years) Daisy (25 years) Archer Daisy Archer Daisy
- 18. Creating Stream From Collection List<String> list = Arrays.asList("a", "b", "c"); Stream<String> stream = list.stream(); String[] array = {"a", "b", "c"}; Stream<String> stream = Arrays.stream(array);
- 19. Creating Stream From an I/O Channel try (Stream<Path> stream = Files.list(Paths.get(“.”));) { … } Stream interface extends AutoCloseable
- 20. Creating Stream Using Generator Functions Stream<Double> stream = Stream.generate(Math::random); Stream<Integer> stream = Stream.iterate(0, n -> n + 3); Both are unbounded
- 21. Parallel Stream From Collection List<String> list = Arrays.asList("a", "b", "c"); Stream<String> stream = list.parallelStream(); From another Stream Stream<String> parallelStream = stream.parallel(); List<String> list = Arrays.asList("a", "b", "c"); Stream<String> stream = list.parallelStream(); Stream<String> parallelStream = stream.parallel();
- 22. Parallel Stream How does it work? Splitting Combining Parallel Processing
- 23. Parallel Stream Performance Impact Always measure performance before using parallel Stream size predictability & Amount of data Decomposability of source data structure Computational Cost
- 24. Stream Intermediate Operators computation creation stateless/stateful Harnessing the power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts
- 26. Intermediate Operators Categories Stream<Integer> stream = Stream.of(3, 2, 1); Stream<Integer> filtered = stream.filter(n -> n % 2 == 0); Filtering Type of stream remains the same Stream<Integer> filtered = stream.filter(n -> n % 2 == 0);
- 27. Intermediate Operators Categories Stream<Integer> stream = Stream.of(3, 2, 1); Stream<String> mapped = stream.map(Object::toString); Mapping Type of stream gets altered (here Integer to String) Stream<String> mapped = stream.map(Object::toString);
- 28. Intermediate Operators Categories Stream<Integer> stream = Stream.of(3, 2, 1); Stream<Integer> sliced = stream.limit(1); Slicing Type of stream remains the same Stream<Integer> sliced = stream.limit(1);
- 29. Stream.of(1, 2, 3, 4) .peek(System.out::println) .filter(n -> n % 2 == 0); Intermediate Operators Laziness Stream.of(1, 2, 3, 4) .peek(System.out::println) .filter(n -> n % 2 == 0) .collect(toList()); Stream.of(1, 2, 3, 4) .peek(System.out::println) .filter(n -> n % 2 == 0); Terminal operator is required to start stream processing Stream.of(1, 2, 3, 4) .peek(System.out::println) .filter(n -> n % 2 == 0) .collect(toList()); Peek will not print anything
- 30. Intermediate Operators Short-Circuiting Stream.of(1, 2, 3, 4) .peek(System.out::println) .filter(n -> n % 2 == 0) .findFirst(); Stream will get short-circuited after the first element is found Peek will print only 1 & 2 Stream.of(1, 2, 3, 4) .peek(System.out::println) .filter(n -> n % 2 == 0) .findFirst();
- 31. Intermediate Operators Stateless vs Stateful Stream.of(1, 2, 3, 4) .peek(System.out::println) .filter(n -> n % 2 == 0) .findFirst(); Stream.of(1, 2, 3, 4) .peek(System.out::println) .sorted(Comparator.reverseOrder()) .filter(n -> n % 2 == 0) .findFirst(); Will cause the whole stream to be traversed All operations are done on current value in stream Stream.of(1, 2, 3, 4) .peek(System.out::println) .sorted(Comparator.reverseOrder()) .filter(n -> n % 2 == 0) .findFirst();
- 32. Stream Collectorscollectreduce Intermediate Operators Terminal Operators computation creation stateless/stateful Lazy & Short-Circuited Harnessing the power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts
- 33. Terminal Operators Single Value Collection Reduce Operation Collect Operation
- 34. Terminal Operators reduce <U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator<U> combiner); Stream.of(3, 2, 1).reduce(0, Integer::sum, Integer::sum); Stream.of(3, 2, 1).reduce(0, Integer::sum); Immutable Reduction Process <U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator<U> combiner); <U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator<U> combiner); <U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator<U> combiner);
- 35. Terminal Operators reduce utility methods Optional<Integer> max = Stream.of(1, 2, 3) .max(Comparator.naturalOrder()); boolean result = Stream.of(1, 2, 3) .anyMatch(n -> n > 2); Optional<Integer> max = Stream.of(1, 2, 3) .max(Comparator.naturalOrder()); boolean result = Stream.of(1, 2, 3) .anyMatch(n -> n > 2);
- 36. Terminal Operators collect Mutable Reduction Process Accumulates elements into a mutable result container Stream.of("a", "b", "c").reduce("", String::concat); String copying = Low Performance !!
- 37. Terminal Operators collect <R> R collect(Supplier<R> supplier, BiConsumer<R, ? super T> accumulator, BiConsumer<R, R> combiner); StringBuilder builder = Stream.of("a", "b", "c").collect( StringBuilder::new, StringBuilder::append, StringBuilder::append ); StringBuilder is the mutable container here
- 38. Terminal Operators Collectors class String joinedString = Stream.of(“a", "b", “c") .collect(Collectors.joining(", ")); IntSummaryStatistics statistics = group.stream() .collect(Collectors.summarizingInt(Person::age)); IntSummaryStatistics{count=10, sum=280, min=26, average=28.000000, max=30} Output: a, b, c String joinedString = Stream.of(“a", "b", “c") .collect(Collectors.joining(", ")); IntSummaryStatistics statistics = group.stream() .collect(Collectors.summarizingInt(Person::age));
- 39. Terminal Operators Downstream Collectors Map<Integer, List<Person>> result = group.stream() .collect(Collectors.groupingBy(Person::age, Collectors.toList())); Map<Integer, List<Person>> result = group.stream() .collect(groupingBy(Person::age)); Divide into different age groups
- 40. Terminal Operators Downstream Collectors Map<Integer, Long> result = group.stream() .collect(groupingBy(Person::age, counting())); Map<Integer, List<String>> result = group.stream() .collect(groupingBy(Person::age, mapping(Person::name, toList()))); Count of people in each age group Names on people in each age group
- 41. Stream Collectorscollectreduce Intermediate Operators Terminal Operators computation creation Primitive Streams stateless/stateful Lazy & Short-Circuited Harnessing the power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts
- 42. Primitive Streams IntStream DoubleStreamLongStream Avoid boxing and unboxing costs Numeric operations are available XXXFunction XXXPredicateXXXSupplierXXXConsumer XXXToXXXFunction Primitive Functional Interfaces
- 43. Primitive Streams Creating from factory methods IntStream intStream = IntStream.range(1, 10); DoubleStream doubleStream = DoubleStream.of(1.0, 2.0); LongStream longStream = LongStream.iterate(0L, n -> n + 4); Generating a range of numbers Stream of known set of numbers Stream using iterative application of a function
- 44. Stream<Person> stream = group.stream(); Primitive Streams Obtaining from Stream<T> mapToXXX flatMapToXXX IntStream intStream = stream.mapToInt(Person::age); OptionalDouble averageAge = intStream.average(); Specialized methods on Primitive Streams IntStream intStream = stream.mapToInt(Person::age);
- 45. Primitive Streams Converting back to Stream<T> Stream<Integer> boxed = IntStream.of(1, 2, 3).boxed();Stream<Integer> boxed = IntStream.of(1, 2, 3).boxed();
- 46. Stream Collectorscollectreduce Intermediate Operators Terminal Operators computation creation Primitive Streams stateless/stateful Lazy & Short-Circuited Harnessing the power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts