Checking how constructor parameters do or do not end up as fields

fields.scala

/*
* bar is not a real field: after the lazy val bork is initialized,
* 'bar' is set to null.
*
* It's a normal field when we make bork a def, add 'val' or 'var' to bar or make it a case class.
* It's not a field at all when we make bork a val.
*/

class MyClass(param: String) {
    lazy val field = param
}

object Runner extends App {
    def printFields(o: Any) = {

      val fields = o.getClass.getDeclaredFields
      val keyValuePairs = fields map { field =>
        field.setAccessible(true)
        println("%10s -> %s" format (field.getName, field.get(o)))
      }
        
    }

    val foo = new MyClass("content")

    println("Before touching field:")
    printFields(foo)
    foo.field
    println("After touching field:")
    printFields(foo)
}