What is the difference between "app" and "app $" in Intellij?

For jvm

HelloWorld$

is the singleton class HelloWorld

.

Scala generates a class ObjectName$

for every object ObjectName

.

It also creates static methods in this class, which looks like this:

public static void main(String[] args) {
  MODULE$.main(args);
}

      

        
        
        
      

    

From, java

you can either get an instance of an object ObjectName

using a static field ObjectName$.MODULE$

, or call static proxy methods on ObjectName$

.