Streams or Loops? Java 8 Stream API by Niki Petkov - Proxiad Bulgaria
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Presentation from the visit of Proxiad Bulgaria - partner for the Java Course in Hack Bulgaria. The topic is the new Stream API in Java 8 and the presenter - Nikolay Petkov from Proxiad Bulgaria
![Source
● Collection.stream()
● Arrays.stream(Object[])
● Stream.of(Object[])
● IntStream.range(int, int)
● BufferedReader.lines();
● Files.list(Path dir)
●
etc.](https://image.slidesharecdn.com/stream-or-loop-proxiad-140723051706-phpapp01/85/Streams-or-Loops-Java-8-Stream-API-by-Niki-Petkov-Proxiad-Bulgaria-14-320.jpg)
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Streams or Loops? Java 8 Stream API by Niki Petkov - Proxiad Bulgaria
- 1. Stream or Loop Java 8 Stream API Nikolay Petkov
- 2. Java 8 Goodies ● Lambda expressions aka functional interfaces ● Method references ● Default methods
- 6. Method Reference ● Static method ● Instance method of particular instance ● Instance method of particular type ● Constructor
- 9. Default Method public interface Developer { void writeCode(); default void writeTest() { throw new ImPerfectException( “Why bother? My code is perfect”); } }
- 10. External vs Internal Iteration for (Car car : cars) { if (“BMW”.equals(car.getBrand()) { car.setOwner(“Alex”) ; } } cars.forEach((car) -> { if (“BMW”.equals(car.getBrand()) { car.setOwner(“Alex”) ; } });
- 11. Stream API Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections. int oldestBmwAge = cars.stream() .filter((car) -> “BMW”.equals(car.getBrand())) .mapToInt((car) -> car.getAge()) .max();
- 12. Streams vs Collections ● Not a storage ● Functional by design ● Possibly unbounded ● Lazy by nature ● Use and discard
- 13. Stream pipeline A stream pipeline consists of: ● a source (such as a Collection, an array, a generator function, or an I/O channel); ● followed by zero or more intermediate operations such as Stream.filter or Stream.map; ● and a terminal operation such as Stream.forEach or Stream.reduce. Execution begins when the terminal operation is invoked, and ends when the terminal operation completes
- 14. Source ● Collection.stream() ● Arrays.stream(Object[]) ● Stream.of(Object[]) ● IntStream.range(int, int) ● BufferedReader.lines(); ● Files.list(Path dir) ● etc.
- 15. Intermediate - filter Returns a stream consisting of the elements of this stream that match the given predicate. Stream<T> filter(Predicate<? super T> predicate) filter((String s) -> s.lenght() < 20) filter((String s) -> String::isEmpty))
- 16. Intermediate - sorted Returns a stream consisting of the elements of this stream, sorted according to the provided Comparator. sorted(Comparator<? super T> comparator) sorted(comparing(Person::getLastName) sorted((s1, s2) -> s1.lenght() > s2.lenght())
- 17. Intermediate - map Returns a stream consisting of the results of applying the given function to the elements of this stream. The map operation is kind of transformation of the stream elements to another elements. map(Function<T,R> mapper) mapToInt((String s) -> s.lenght()) map((User u) -> User::getRole())
- 18. Terminal – max/min/sum/count Returns the maximum/minimum element of this stream according to the provided Comparator max(Comparator<? super T> comparator) max(comapring(Persone::getAge)) stream.mapToInt(Persone::getAge).sum()
- 19. A lot more follows Questions?