Question

I’m having trouble figuring out how to get the type parameter of Option when the type parameter is Int

I tried the following code:

class TestClass {
  val intField: Option[Int] = Some(1)
}

val cls = new TestClass
val field = cls.getDeclaredField("intField")
val typeParams = field.getGenericType.asInstanceOf[ParameterizedType].getActualTypeArguments

typeParams gives me java.lang.Object

my question is how do I get it to return java.lang.Integer to me

Answer 1

The exact generic type information is lost at run-time. See Reflecting generics and note:

…while the JVM will not track the actual type arguments for instances of a generic class, it does track the actual type arguments for subclasses of generic classes.

There are no subclasses here — hence the reason for Object and not Integer. Perhaps look into Manifests (a Scala trick for implicit reified types)?

Happy coding.