Why does Scala place a dollar sign at the end of class names?

Question

In Scala when you query an object for either its class or its class name, you'll get a rogue dollar sign ("$") at the tail end of the printout:

object DollarExample {   def main(args : Array[String]) : Unit = {     printClass()   }    def printClass() {     println(s"The class is ${getClass}")     println(s"The class name is ${getClass.getName}")   } } 

This results with:

The class is class com.me.myorg.example.DollarExample$ The class name is com.me.myorg.example.DollarExample$ 

Sure, it's simple enough to manually remove the "$" at the end, but I'm wondering:

• Why is it there?; and
• Is there anyway to "configure Scala" to omit it?

Answer 1

What you are seeing here is caused by the fact that scalac compiles every object to two JVM classes. The one with the $ at the end is actually the real singleton class implementing the actual logic, possibly inheriting from other classes and/or traits. The one without the $ is a class containing static forwarder methods. That's mosty for Java interop's sake I assume. And also because you actually need a way to create static methods in scala, because if you want to run a program on the JVM, you need a public static void main(String[] args) method as an entry point.

scala> :paste -raw // Entering paste mode (ctrl-D to finish)  object Main { def main(args: Array[String]): Unit = ??? }  // Exiting paste mode, now interpreting.   scala> :javap -p -filter Main Compiled from "<pastie>" public final class Main {   public static void main(java.lang.String[]); }  scala> :javap -p -filter Main$ Compiled from "<pastie>" public final class Main$ {   public static Main$ MODULE$;   public static {};   public void main(java.lang.String[]);   private Main$(); } 

I don't think there's anything you can do about this.

Answer 2

Although all answer that mention the Java reflection mechanism are correct this still doesnot solve the problem with the $ sign or the ".type" at the end of the class name.

You can bypass the problem of the reflection with the Scala classOf function.

Example:

println(classOf[Int].getSimpleName) println(classOf[Seq[Int]].getCanonicalName) => int => scala.collection.Seq => Seq 

With this you just have the same result as you have in for example Java