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![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);](https://image.slidesharecdn.com/java8streamsindicthreads-160605125949/85/Harnessing-the-Power-of-Java-8-Streams-18-320.jpg)
![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);](https://image.slidesharecdn.com/java8streamsindicthreads-160605125949/75/Harnessing-the-Power-of-Java-8-Streams-18-2048.jpg)
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Harnessing the Power of Java 8 Streams
The document discusses Java 8 Streams, emphasizing their use in declarative programming and internal iteration. It covers key concepts like intermediate and terminal operations, stream creation, parallel processing, and the advantages of using Streams for efficient data handling and manipulation. Various examples demonstrate how Streams simplify coding practices compared to traditional imperative approaches.
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Harnessing the Power of Java 8 Streams
- 1. Harnessing the powerof Java 8 Streams Praveer Gupta
- 2. Default Methods Lambda Expressions Streams Date-TimeAPI CompletableFuture Optional
- 3. helps to makea 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 “Thereare 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 Harnessingthe power Java 8 Streams Programming Paradigm Concepts
- 6. Stream Collectorscollectreduce Intermediate Operators Terminal Operators computationcreation 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 powerJava 8 Streams Declarative Programming Internal Iteration Programming Paradigm Concepts
- 8. Declarative SELECT NAME FROMPERSON 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 vsNew 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 interfaceCustomerRepository { List<Customer> findByCity(String cityName); } API Definition
- 12. Application of Streams interfaceCustomerRepository { 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 thepower Java 8 Streams Declarative Programming Internal Iteration Programming Paradigm Concepts
- 14. Stream a read-only sequenceof elements computational operations that will be performed in aggregate Collection efficient management of elements efficient access to elements
- 15.
- 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 (25years) 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 anI/O Channel try (Stream<Path> stream = Files.list(Paths.get(“.”));) { … } Stream interface extends AutoCloseable
- 20. Creating Stream Using GeneratorFunctions 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 doesit work? Splitting Combining Parallel Processing
- 23. Parallel Stream Performance Impact Alwaysmeasure 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 Harnessingthe power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts
- 25.
- 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 computationcreation stateless/stateful Lazy & Short-Circuited Harnessing the power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts
- 33. Terminal Operators Single ValueCollection Reduce Operation Collect Operation
- 34. Terminal Operators reduce <U> Ureduce(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 utilitymethods 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 ReductionProcess Accumulates elements into a mutable result container Stream.of("a", "b", "c").reduce("", String::concat); String copying = Low Performance !!
- 37. Terminal Operators collect <R> Rcollect(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 StringjoinedString = 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 computationcreation 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 Avoidboxing and unboxing costs Numeric operations are available XXXFunction XXXPredicateXXXSupplierXXXConsumer XXXToXXXFunction Primitive Functional Interfaces
- 43. Primitive Streams Creating fromfactory 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 backto 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 computationcreation Primitive Streams stateless/stateful Lazy & Short-Circuited Harnessing the power Java 8 Streams Declarative Programming Internal Iteration chained categories Programming Paradigm Concepts
- 47.