How a val value bean changed

Question

I use scala with mybatis:

Space.scala:

case class Space(
              val id: Long ,
              spaceName:String)

SpaceDao:

   val space=Space(0,"space name")
   val mapper = session.getMapper(classOf[SpaceMapper])
   val result = mapper.insertSpace(space)
   println(space.id)

The result space id is the auto increment number of mysql, not 0. but both space and space.id is val, why a val value can be changed?

Answer 1

This can be achieved via reflection (which is used by SetFieldInvoker ):

Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine. This is a relatively advanced feature and should be used only by developers who have a strong grasp of the fundamentals of the language. With that caveat in mind, reflection is a powerful technique and can enable applications to perform operations which would otherwise be impossible.

Also see this question .