Scala. A Java jövője. Háber János

Transcription

1 Scala A Java jövője Háber János

2 Scala > Java? - JVM-en fut - Típusos - Teljesen objektum orientált - Funkcionális programozás támogatása - Minta illesztés - Többszörös öröklődés (Mixin) - Implicit konverzió - Actor alapú konkurencia kezelés - Ruby szerű szintaxis és még sok minden

3 Scala + Java - Egyszerre használható Java és Scala ugyanabban a projektben - Használhatók a meglévő Java libek - IDE támogatás - Ha valami nem megy, csináld Jávában

4 Teljesen Objektum orientált //Minden érték egy objektum 1.toString //Minden művelet egy metódus hívás > (1).+(2).+(3) //. és ( ) elhagyható "abc" charat 1 -> "abc".charat(1)

5 Hello World //Java public class HelloWorld { public static void main(string[] args) { String message = "Hello World"; System.out.println(message); //Scala object HelloWorld { def main(args:array[string]):unit = { val message = "Hello World" println(message)

6 Singleton támogatás object Hello { def world = "Hello World" Hello.world //Hello$.class import scala.scalaobject; public final class Hello$ implements ScalaObject { private Hello$() { MODULE$ = this; public String world() { return "Hello World"; public static final MODULE$; static { new (); //Hello.class import public final class Hello { public static final String world() { return Hello..MODULE$.world();

7 Automatikus getter/setter class SimpleVal { val finalvalue: String = "hi" var simplevariable: String = "" import scala.scalaobject; import = "...removed...") public class SimpleVal implements ScalaObject { private final String finalvalue = "hi"; private String simplevariable = ""; public String finalvalue() { return this.finalvalue; public String simplevariable() { return this.simplevariable; public void simplevariable_$eq(string paramstring) { this.simplevariable = paramstring;

8 Scala - tömör //Java public class Person { private final String name; private final int age; public Person(String name,int age) { this.name = name; this.age = age; //Scala class Person(val name:string, val age:int) public String getname() { return name; public int getage() { return age;

9 Scala - tömör //Java public class Person { private String name; private int age; public Person(String name,int age) { this.name = name; this.age = age; public String getname() { return name; //Scala import reflect.beanproperty class Person var name: String = var age: Int = _ public int setname(string name) { this.name=name; public String getage() { return age; public int setage(string age) { this.age=age;

10 Típus következtetés val sum = val nums = List(1, 2, 3) val map = Map("abc" -> List(1, 2, 3)) val sum: Int = val nums: List[Int] = List(1, 2, 3) val map: Map[String, List[Int]] = Map("abc" -> List(1, 2, 3))

11 Duck typing object BigDuck { def quack(value: String) = { value.touppercase object SmallDuck { def quack(value: String) = { value.tolowercase object IamNotReallyADuck { def quack(value: String) = { "prrrrrp" def quacker(duck: {def quack(value: String): String) { println (duck.quack("quack")) quacker(bigduck) quacker(smallduck) quacker(iamnotreallyaduck) class MyDao[T <: {def id : K, K]

12 High-order funkciók def transaction(function: => Any): Any = { //... transaction { //here your database code

13 High-order funkciók def measure[t](func: => T):T = { val start = System.nanoTime() val result = func val elapsed = System.nanoTime() - start println("the execution of this call took: %s ns".format(elapsed)) result def mycallback = { Thread.sleep(1000) "I'm a callback" val result = measure(mycallback) > The execution of this call took: ns

14 High-order funkciók import org.scalatest.funsuite import scala.collection.mutable.stack class ExampleSuite extends FunSuite { test("pop is invoked on an empty stack") { val emptystack = new Stack[Int] intercept[nosuchelementexception] { emptystack.pop() assert(emptystack.isempty)

15 Scala - minta illesztés - Hasonló a Java switch-hez - Bármilyen típusú adatra használható - Első találat szabály def matchtest(x: Any): Any = x match { case => "one" case "two" => 2 case a: Int if (a > 100) => a - 3 case b: Int => b + 3 case _ => "None of above"

16 Option def div(a:int)(b:int):option[int] = if (b <= 0) None else if (a < b) Some(0) else Some(1 + div(a - b)(b).get) div(25)(5) div(150)(2) div(13)(4) div(13)(0) div(25)(-5) // => Some(5) // => Some(75) // => Some(3) // => None // => None div(13)(0) match { case Some(x) => println(x) case None => println("problems") // => prints "Problems" div(25)(5) match { case Some(x) => println(x) case None => println("problems") // => prints "5"

17 Implicit konverzió implicit def doubletoint(d: Double) = d.toint val x: Int = 42.0 //Java public <T> void javanomanifest(class<t> clazz) { //... //Scala def manifesttest[t](implicit m:manifest[t]) = { m.runtimeclass

18 Operátor túlterhelés class Complex(val real : Double, val imag : Double) { def +(that: Complex) = new Complex(this.real + that.real, this.imag + that.imag) def -(that: Complex) = new Complex(this.real - that.real, this.imag - that.imag) override def tostring = real + " + " + imag + "i" object Complex { def main(args : Array[String]) : Unit = { var a = new Complex(4.0,5.0) var b = new Complex(2.0,3.0) println(a) // i println(a + b) // i println(a - b) // i

19 Trait-ek //Hasonló a Java interfacehez trait Language { val name:string //De tartalmazhat implementációt is override def tostring = name

20 Trait-ek trait JVM { override def tostring = super.tostring + " runs on JVM" trait Static { override def tostring = super.tostring + " is Static" //A trait-ek összefűzhetők (a sorrend számít!) class Scala extends Language with JVM with Static { val name="scala" println(new Scala()) // -> "Scala runs on JVM is Static"

21 Trait-ek trait Quacking { def quack() = { println("quack quack quack!") class Duck { val version = "ACME Inc. Generic Duck v1.0" val aduck = new Duck with Quacking aduck.quack()

22 Case Class abstract class Term case class Var(name: String) extends Term case class Fun(arg: String, body: Term) extends Term case class App(f: Term, v: Term) extends Term val x1 = Var("x") val x2 = Var("x") val y1 = Var("y") println("" + x1 + " == " + x2 + " => " + (x1 == x2)) println("" + x1 + " == " + y1 + " => " + (x1 == y1)) def printterm(term: Term) { term match { case Var(n) => print(n) case Fun(x, b) => print("^" + x + ".") printterm(b) Var(x) == Var(x) => true Var(x) == Var(y) => false case App(f, v) => Console.print("(") printterm(f) print(" ") printterm(v) print(")")

23 Scala Java Interoperability class Companion { def hello() { println("hello (class)") // [1] object Companion { def hallo() { println("hallo (object)") // [2] def hello() { println("hello (object)") // [3] public class TestCompanion { public static void main(string[] args) { new Companion().hello(); // [1] Companion.hallo(); // [2] (static) Companion$.MODULE$.hello(); // [3] (static)

24 Multiline String és Beágyazott XML val somexmlinastring = """ <sammich> <bread>wheat</bread> <meat>salami</meat> <condiments> <condiment expired="true">mayo</condiment> <condiment expired="false">mustard</condiment> </condiments> </sammich> """ import scala.xml._ val somexml = <sammich> <bread>wheat</bread> <meat>salami</meat> <condiments> <condiment expired="true">mayo</condiment> <condiment expired="false">mustard</condiment> </condiments> </sammich>

25 Információk org/docu/files/scalabyexample.pdf

26 Köszönöm a figyelmet Elérhetőség: janos.haber@finesolution.hu