Question

I’m really new to Scala, and I’ve come across an error I am unable to solve by myself or through internet searches.

I have a Scala class called “GUI” that represents a JFrame along with a companion class. When I try to import the companion class using import GUI._ I get the error “stable identifier required, but GUI.this.GUI() found”.

I made an empty class and companion object and the import worked fine, so I assume that the error is related to something specific to my code. Below is the code in question:

object GUI {

   def test:Integer = 1
}

class GUI extends JFrame{

import GUI._
val ICON_LOCATION:File = new File("Images/iMovies.ico");
val ICON:BufferedImage = Ootil.createImage("iMovies.png");
val TITLE:String = "iVideos";
val LICENSE_NAME:String = "OpenBSD";

def GUI(){
    setLayout(new BorderLayout());

    createGUI();

    pack();
    setSize(100,100);
    setLocationRelativeTo(null);
    setVisible(true);
}

def versionMajor: Integer = 1
def versionMinor: Integer = 0
def versionRevision: Integer = 0
def versionPreReleaseID: String = "alpha"
def versionBuildNumber: String = "1b"

private def createGUI():Unit = {
        val panel = new JPanel();
        panel.setLayout(new BorderLayout());


        add(panel, BorderLayout.CENTER);
}

def getIcon():BufferedImage = ICON

def getProgramTitle():String = TITLE

def getConfigOptions():LookAndFeelConfigurationOptions = GUIConfigOptions.CONFIG_OPTIONS;
}

Answer 1

To add to Kipton’s answer, there’s nothing wrong with doing:

class GUI{
  def GUI() {
    println("something")
  }
}

But the result won’t be a constructor — it will be an ordinary method.

val a = new GUI() won’t print anything, but calling a.GUI() will.

This is why you didn’t get an error message about defining your constructor incorrectly.

---

When you run the command import GUI._, Scala needs GUI to always evaluate to the same object. This is only the case when GUI is an object, a package, or a val.

In your code, import GUI._ referred to the method GUI that you defined, because the GUI method is defined in a closer scope than object GUI (the fact that the compiler hasn’t encountered the definition of def GUI yet doesn’t make a difference).

Since import GUI._ referred to the method GUI, which is not a val, object, or package, you got the error message about GUI not being a stable identifier.