Stuck at “Hello World” with IntelliJ IDEA 9.0.1 for Scala

Question

I've been using Eclipse since 2.x and IDEs in general for over 20 years (since Turbo Pascal and Turbo C in the late '80s!).

(that preamble is supposed to imply, "I'm not an idiot" ... but doesn't sound so smart as I read it... LOL :-] )

Now I'm trying to use the Scala debugger in IntelliJ 9.0.1. I've resigned myself to an old standby, the "hello world" trick to check if the environment is setup correctly:

class hello {
  def main(a: Array[String]) = println("got args: " + a)
}

I also tried this version, just in case:

object hello extends Application {
    println("hi")
}

Alas, I'm unable to get even this simple Scala example to run. I'd like to eventually put a breakpoint in it, but for now just running it would be great. I have Java 1.6u20 and the Scala plug-in 0.3.473 (January 2010). The error below summarizes my experience:

What possibly could I be doing wrong?

Thanks

Answer 1

From your screenshot it looks like you were using:

class hello {
  def main(a: Array[String]) = println("got args: " + a)
}

The main method has to be on an object to support a main method.

Capitalizing the object / class name is the convention but it isn't enforced.

Answer 2

When you change your implementation from class to object, it works like a charm:

object Hello {
   def main(a: Array[String]) = println("got args: " + a)
}

I picked up this little, but important difference here: http://sonyarouje.com/2011/03/18/running-scala-in-intellij-idea-10/

Answer 3

It may be a bug in the plugin. If you define you object as Hello (capitalized) then it works, at least on my machine.

Answer 4

Is your file called hello.scala? (I can't see that it has the .scala extension in your screenshot) - it must be a .scala file as otherwise the compiler will not be able to compile it