scala-java-interop

Scala's Option class has an orNull method, whose signature is shown below. orNull [A1 >: A](implicit ev : <:<[Null, A1]) : A1 I'm bewildered by the implicit thing. Would somebody please explain how it can be used, ideally with an example? scala> Some(1).orNull <console>:10: error: could not find implicit value for parameter ev: <:<[Null,Int] Some(1).orNull ^ scala> (None : Option[Int]).orNull <console>:10: error: could not find implicit value for parameter ev: <:<[Null,Int] (None : Option[Int]).orNull scala> Some("hi").orNull res21: java.lang.String = hi scala> Some(null : String).orNull res22

In a previous question, Accessing scala.None from Java , it seems that people had used javap to figure out how to access scala.None from Java. I would like to know how they did that. FYI, the answer is: scala.Option$.MODULE$.apply(null); which can be shorted to: scala.Option.apply(null); Given this program ( OptionTest.scala ): object OptionTest extends App { val x = scala.None val y = scala.Some("asdf") } I ran javap on it like this: javap -s -c -l -private OptionTest This is a portion of the javap output: public static final scala.None$ x(); Signature: ()Lscala/None$; Code: 0: getstatic #11;

I'm trying to inject some Scala code into my existing Java app. (So, being said, I want some more fun). I create a singleton stuff in Scala ScalaPower.scala package org.fun class ScalaPower object ScalaPower{ def showMyPower(time:Int) = { (0 to time-1).mkString(", ") } } Now, inside OldJava.java class OldJava { public void demo(){ System.out.println(?) } } What should I fill in ? so that Java will call the showMyPower method? I tried both org.fun.ScalaPower.showMyPower(10) and org.fun.ScalaPower.getInstance().showMyPower(10) but none work. (Decompile the class file using Jad show me nothing

I think I understand the new "value class" feature of Scala 2.10, by comparison with Haskell's newtype : trait BoundedValue[+This] extends Any { this: This => def upperBound: This def lowerBound: This } class Probability @throws(classOf[IllegalArgumentException]) (v: Double) extends AnyVal with BoundedValue[Probability] { val value: Double = if ((v >= 0.0) && (v <= 1.0)) v else throw new IllegalArgumentException((v.toString) + "is not within the range [0.0, 1.0]") override val upperBound: Probability = new Probability(0.0) override val lowerBound: Probability = new Probability(1.0) //

I would like to create a Java class that follows the Scala setters/getters convention. I tried following simple class, but it does not work: public class JavaA { private int a = 0; public int a() { return a; } public void a_$eq(int a) { this.a = a; } } But when I try to access it from scala: val x = new JavaA x.a = 1 and I get "reassignment to val" error message. I tried to look for this, but all issues I found where the other way around from scala to java. What is the right way to do it? Thanks! You can only sort of do this, and it's hard enough that you probably don't want to. What you can't

Ｉhave some codes written in Java. And for new classes I plan to write in Scala. I have a problem regarding accessing the protected static member of the base class. Here is the sample code: Java code: class Base{ protected static int count = 20; } scala code: class Derived extends Base{ println(count); } Any suggestion on this? How could I solve this without modifying the existing base class This isn't possible in Scala. Since Scala has no notation of static you can't access protected static members of a parent class. This is a known limitation . The work-around is to do something like this: //

Starting with Scala version 2.9 there exists a handy converter to convert from java.util.List and other collections to Scala's data structures by writing something like this: import scala.collection.JavaConverters._ def scalaVersion = callJavaMethod.asScala This is a lovely little feature, as it allows one to exploit the advantages of Scala when interacting with existing Java code. However, I am uncertain about the involved time and space complexity and could not find anything in the official documentation, hence, the following question: Where can I get information on the complexity (time and

I have a Java Future object which I would like to convert into a Scala Future . Looking at the j.u.c.Future API, there is nothing much that I could use other than the isDone method. Is this isDone method blocking? Currently this is what I have in my mind: val p = Promise() if (javaFuture.isDone()) p.success(javaFuture.get) Is there a better way to do this? How about just wrapping it (I'm assuming there's an implicit ExecutionContext here): val scalaFuture = Future { javaFuture.get } EDIT: A simple polling strategy could look like this (java.util.Future => F): def pollForResult[T](f: F[T]):