Lambda выражения и Java 8
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The document discusses Java 8 lambda expressions and functional interfaces. Key points include: - Lambda expressions allow for anonymous methods that can access local variables and don't require a class file. - Functional interfaces define a single abstract method, representing a function contract. - Default methods allow interfaces to provide default implementations of methods. - Method references provide a way to refer to a method without invoking it.
![ТЕОРИЯ, ССЫЛКА НА МЕТОД
“A method reference is used to refer to a method without invoking it;
a constructor reference is similarly used to refer to a constructor without
creating a new instance of the named class or array type.” - JSR
System::getProperty
"abc"::length
String::length
super::toString
ArrayList::new
int[]::new
14 Sigma Ukraine](https://image.slidesharecdn.com/closurespresentation-130309030939-phpapp01/85/Lambda-Java-8-14-320.jpg)
Lambda выражения и Java 8
- 1. LAMBDA IN JAVA 8 MIKE PONOMARENKO
- 2. ТЕОРИЯ Что такое замыкание (Lambda Expressions, JSR 335) Изменения в языке Сопутствующие изменения 2 Sigma Ukraine
- 3. JSR 335 EARLY DRAFT R3
- 4. ТЕОРИЯ - ЗАМЫКАНИЯ Lambda expression – Анонимный метод – Может обращаться к переменным в локальной области – Нет лишнего .class при компиляции (x, y) => { System.out.println("The sum of x and y equals " + (x+y) ) () => {return outerValue;} 4 Sigma Ukraine
- 5. ПРИМЕР error: local variables referenced from a lambda expression must be final or effectively final { String ref = "a"; Runnable r = () -> {ref = "b";}; r.run(); System.out.println(ref); } 5 Sigma Ukraine
- 6. ПРИМЕР { Runnable r = ()->{System.out.println("hello");}; (new Thread(r)).start(); } 6 Sigma Ukraine
- 7. ПРИМЕР { String ref = "a"; Runnable r = () -> {System.out.println(ref);}; r.run(); System.out.println(ref); } 7 Sigma Ukraine
- 8. ПРИМЕР String ref = "a"; Runnable r = new Runnable(){ public void run(){ System.out.println(ref); } }; r.run(); System.out.println(ref); 8 Sigma Ukraine
- 9. ПРИМЕР { List<String> strings = new LinkedList<String>(); Collections.sort(strings, (String a,String b) -> { return -(a.compareTo(b)); }); } 9 Sigma Ukraine
- 10. ПРИМЕР { List<String> strings = new LinkedList<String>(); Collections.sort(strings, (a, b) -> -(a.compareTo(b))); } 10 Sigma Ukraine
- 11. ТЕРИЯ, ИЗМЕНЕНИЯ В ЯЗЫКЕ Функциональный интерфейс – “A functional interface is an interface that has just one abstract method, and thus represents a single function contract. (In some cases, this "single" method may take the form of multiple abstract methods with override-equivalent signatures inherited from superinterfaces; in this case, the inherited methods logically represent a single method.)” - JSR Метод по умолчанию Ссылка на метод 11 Sigma Ukraine
- 12. ТЕОРИЯ, МЕТОД ПО УМОЛЧАНИЮ interface A{ void doA(); } interface B extends A{ default void doB() { doA(); doA(); } } 12 Sigma Ukraine
- 13. ТЕОРИЯ, МЕТОД ПО УМОЛЧАНИЮ interface A{ void doA(); default void doB() { doA(); doA(); } } 13 Sigma Ukraine
- 14. ТЕОРИЯ, ССЫЛКА НА МЕТОД “A method reference is used to refer to a method without invoking it; a constructor reference is similarly used to refer to a constructor without creating a new instance of the named class or array type.” - JSR System::getProperty "abc"::length String::length super::toString ArrayList::new int[]::new 14 Sigma Ukraine
- 15. ПРИМЕР Collection<String> c = Arrays.asList("A","B","CD"); System.out.println(sum(c,String::length)); 15 Sigma Ukraine
- 16. ПРИМЕР interface Code<T,R>{ R exec(T input); } public static <T,R extends Number> long sum(Collection<T> c ,Code<T,R> cd){ long rz = 0; for(T t : c){ R v = cd.exec(t); if(v!=null) { rz+=v.longValue(); } } return rz; } 16 Sigma Ukraine
- 17. ПРИМЕР import java.util.function.*; public static <T,R extends Number> long sum(Collection<T> c , Function<T,R> cd){ long rz = 0; for(T t : c){ R v = cd.apply(t); if(v!=null) { rz+=v.longValue(); } } return rz; } 17 Sigma Ukraine
- 18. JDK System.out.println(c.stream().map(String::length).sum()); 18 Sigma Ukraine
- 19. ТЕОРИЯ Добавляется в рантайм Множественное наследование поведения. Похоже на “C# extension methods” Наследование – 1. Суперкласс (“class wins”) 2. Более спецефичный интерфейс (“subtype wins”) 3. Делать вид что метод абстрактный 1. Реализующий класс должен сделать выбор сам. A.super.m() 19 Sigma Ukraine
- 20. JDK interface Iterator<T> { boolean hasNext(); T next(); default void remove() { throw new UnsupportedOperationException(); } } 20 Sigma Ukraine
- 21. JDK interface Collection – forEach – removeIf(Predicate) – stream() – parallelStream() 21 Sigma Ukraine
- 22. JDK default Stream<E> stream() { return Streams.stream(() -> Streams.spliterator(iterator(), size(), Spliterator.SIZED), Spliterator.SIZED); } default Stream<E> parallelStream() { return stream().parallel(); } 22 Sigma Ukraine
- 23. JDK public interface Stream<T> extends BaseStream<T, Stream<T>> { Stream<T> filter(Predicate<? super T> predicate); <R> Stream<R> map(Function<? super T, ? extends R> mapper); Stream<T> sorted(); Optional<T> reduce(BinaryOperator<T> reducer); default Optional<T> max(Comparator<? super T> comparator) { return reduce(Comparators.greaterOf(comparator)); } boolean anyMatch(Predicate<? super T> predicate); } 23 Sigma Ukraine
- 24. JDK System.out.println(c.stream().map(String::length).sum()); 24 Sigma Ukraine
- 25. Thank you for your attention!