Java8

Java8

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  first taste ofJava 8 Sunil Kumar | Wiley London | 22-01-2014
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  Java 8 features ● Lambda ● Interface improvement ● Streams ● new packages Keywords : Big data, Parallelism, Cloud computing
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  1. Lambda (anonymousfunction) In mathematics and computing generally, a lambda expression is a function: for some or all combinations of input values it specifies an output value. Lambda expressions in Java introduce the idea of functions into the language Ex: 0 param Runnable r = () -> System.out.println("hello world"); r.run(); // prints "hello world" Object o = () -> System.out.println("hello world"); //won’t compile Ex: 1 param FileFilter filter = f -> f.getAbsolutePath().endsWith(".txt"); return filter.accept(new File("myfile.txt")); // returns true
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  Lambda - syntax Lambda expression has three part : parenthesized params, arrow and body ● (parameters) -> expression ● (parameters) -> {statements…} Type inference Comparator<String> c = (lhs, rhs) -> { System.out.println("comparing : " + lhs + " to " + rhs); return lhs.compareTo(rhs); }; int result = c.compare(“hello”, “world”)
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  More examples List<Apple>inventory = Arrays.asList(new Apple(80,"green"), new Apple(155, "green"), new Apple(120, "red")); // [Apple{color='green', weight=80}, Apple{color='green', weight=155}] List<Apple> greenApples2 = filterApples(inventory, (Apple a) -> "green".equals(a.getColor())); System.out.println(greenApples2); // [Apple{color='green', weight=155}] List<Apple> heavyApples2 = filterApples(inventory, (Apple a) -> a.getWeight() > 150); System.out.println(heavyApples2); public static List<Apple> filterApples(List<Apple> inventory, Predicate<Apple> p){ List<Apple> result = new ArrayList<>(); for(Apple apple : inventory){ if(p.test(apple)){ result.add(apple); }} return result; }
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  Method References Methodreferences are compact lambda expressions for methods that already have a name. ● String::valueOf x -> String.valueOf(x) ● Object::toString x -> x.toString() ● x::toString () -> x.toString() ● ArrayList::new () -> new ArrayList<>()
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  2. Interface improvement (Functional interface) A functional interface is one whose type can be used for a method parameter when a lambda is to be supplied as the actual argument. For example, the forEach method on collections could have the following signature: public void forEach(Consumer<? super T> consumer); More precisely, a functional interface is defined as any interface that has exactly one explicitly declared abstract method. ● interface can now define static methods. ● interfaces can now provide default methods (The qualification is necessary because an interface may have non-abstract default methods.) This is why functional interfaces used to be called Single Abstract Method (SAM) interfaces, a term that is still sometimes seen.
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  3. Streams Astream is a sequence of values. Allows functional-style operations on streams of values. Stream<T> stream = collection.stream(); Stream<T> stream = collection.parallelStream();
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  Steams type OperationsInterface Used lambda signature return type return value Sample lazy/intermediate operations filter Predicate<T> T -> boolean Stream<T> stream containing input elements that satisfy the Predicate map Function<T, R> T -> R Stream<R> stream of values, the result of applying the Function to each input element sorted Comparator<T> (T, T) -> int Stream<T> stream containing the input elements, sorted by the Comparator Sample eagar/terminal operation reduce BinaryOperator<T> (T, T) -> T Optional<T> forEach Consumer<T> T -> void void
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  4. java.util.function Function<T,R> - take T as input, return R as output Predicate<T> - take T as input, return a boolean as output Consumer<T> - take T as input, don't return anything Supplier<T> - take no input, return T BinaryOperator<T> - take two T's as input, return one T as output
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  Thank You. Q& A.
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  Reference: ● http://www.lambdafaq.org/ ● http://www.infoq.com/news/2013/08/everything-about-java-8 ● https://blogs.oracle.com/thejavatutorials/entry/jdk_8_documentation_developer_preview ● http://sett.ociweb.com/sett/settFeb2013.html ● http://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html ● https://github.com/java8/LambdasInAction