why doesn't scala recognize com.vaadin.ui.MenuBar.MenuItem

Question

I'm trying to create a Vaadin window with a MenuBar using Scala. I'm getting a compiler error that indicates that the com.vaadin.ui.MenuBar.MenuItem import can't be found. I've looked at the Vaadin library (6.4.8), and it appears that the class is there:

com/vaadin/ui/MenuBar$Command.class
com/vaadin/ui/MenuBar$MenuItem.class
com/vaadin/ui/MenuBar.class

Here is the class structure from the MenuBar source:

@SuppressWarnings("serial")
@ClientWidget(value = VMenuBar.class, loadStyle = LoadStyle.LAZY)
public class MenuBar extends AbstractComponent { 
   ... 
   public interface Command extends Serializable { ... }
   public class MenuItem implements Serializable { ... }

}

For demo purposes, here's a sample Scala class:

import com.vaadin.Application
import com.vaadin.ui.Button
import com.vaadin.ui.Window
import com.vaadin.ui.MenuBar
import com.vaadin.ui.MenuBar.Command
import com.vaadin.ui.MenuBar.MenuItem

class MyVaadinApplication extends Application
{

    private var window : Window = null

    override def init() =
    {
        window = new Window("My Scala Vaadin Application")
        setMainWindow(window)
        window.addComponent(new Button("Click Me"))
    }

}

And here's the resulting error when I try to compile it:

/Users/jstanford/Development/NetBeansProjects/TraderDashboard/src/main/scala:-1: info: compiling
Compiling 2 source files to /Users/jstanford/Development/NetBeansProjects/TraderDashboard/target/classes at 1291973683915
[ERROR]MyVaadinApplication.scala:7: error: MenuItem is not a member of com.vaadin.ui.MenuBar
import com.vaadin.ui.MenuBar.MenuItem
       ^

Can anyone spot the problem here?

Thanks, John

Answer 1

Inner classes cannot be imported as usual it is appropriate for Java. Just specify type projections as it's done for Button#ClickEvent type:

import com.vaadin._
import ui._
import Button._

class MyScalaVaadinApplication extends Application {
  val window = new Window("My Vaadin Application")

  def init {
    window.addComponent(new Button("Click Me", new ClickListener {
      def buttonClick(clickEvent: Button#ClickEvent): Unit = window.showNotification("Just a message")
    }))

    setMainWindow(window)
  }
}

Answer 2

A very simple example showing what's going on.

Java:

package a;
public class Outer { public class Inner {} }

Scala:

import a.Outer
import a.Outer.Inner // causes *Inner is not a member of a.Outer*

Notice that Inner, like MenuBar.MenuItem, is a non-static inner class and as such is associated with one instance of Outer. But Scala allows us to import Inner using a instance of Outer:

import a.Outer
import a.Outer.Inner

object dummy {
  val o = new Outer
  val o2 = new Outer
  import o.Inner
  val i = new Inner
  val i2 = new o2.Inner
}

If we could just import a.Outer.Inner how would the compiler know to which instance of Outer is Inner supposed to belong to?

Hope the issue has been cleared.