Question

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 but nonsense code.)

Edit
I remove the class ScalaPower declaration and scala produce the static method as expected. (call to org.fun.ScalaPower.showMyPower(10) just works).

Wonder if it’s a bug in scala compiler or not

Answer 1

I think this indirectly covers it:

Companion Objects and Java Static
Methods

There is one more thing to know about
companion objects. Whenever you define
a main method to use as the entry
point for an application, Scala
requires you to put it in an object.
However, at the time of this writing,
main methods cannot be defined in a
companion object. Because of
implementation details in the
generated code, the JVM won’t find the
main method. This issue may be
resolved in a future release. For now,
you must define any main method in a
singleton object (i.e., a
“non-companion” object) [ScalaTips].
Consider the following example of a
simple Person class and companion
object that attempts to define main.

As found here: http://programming-scala.labs.oreilly.com/ch06.html

In short because your Object is a companion object (has a companion class) you can’t call it like you expect. As you found if you get rid of the class it will work.