A singleton that performs side-effects on "construction"

Well, seems laziness keeps catching me and doesn't want to let me off-hook.
Now there's the objects in scala, which are nice singletons. But they don't
construct themselves as do the classes. Compare e.g.

class A1 {
case object X
println(" ... ")
}

and

object A2 {
case object X
println(" --- ")
}

even

new (A1.X) == A2.X

won't trigger the body of object A2 being executed. Is this considered a
feature btw? So how can I write code that is run inside the object when it's
"constructed" [without explicitely calling it myself] ?

-Martin