The chapter 31 of the same “Programming in Scala” is more precise:
Java has no exact equivalent to a singleton object, but it does have static methods.
The Scala translation of singleton objects uses a combination of static and instance methods. For every Scala singleton object, the compiler will create a Java class for the object with a dollar sign added to the end.
For a singleton object namedApp
, the compiler produces a Java class namedApp$
.
This class has all the methods and fields of the Scala singleton object.
The Java class also has a single static field namedMODULE$
to hold the one
instance of the class that is created at run time.
As a full example, suppose you compile the following singleton object:
object App {
def main(args: Array[String]) {
println("Hello, world!")
}
}
Scala will generate a Java App$ class with the following fields and methods:
$ javap App$
public final class App$ extends java.lang.Object
implements scala.ScalaObject{
public static final App$ MODULE$;
public static {};
public App$();
public void main(java.lang.String[]);
public int $tag();
}
That’s the translation for the general case.