How in Scala , trait "Null" can be instantiated producing "null"?

Question

From the API doc I found that Null is a trait, but it says its sole instance is null.

abstract final class Null extends AnyRef

Null is - together with scala.Nothing - at the bottom of the Scala type hierarchy.

Null is a subtype of all reference types; its only instance is the null reference. Since Null is not a subtype of value types, null is not a member of any such type. For instance, it is not possible to assign null to a variable of type scala.Int.

How is it possible to instantiate a trait? Any simple example to realize this concept would really helpful.

Answer 1

You cannot instantiate an instance of the class Null, as it is abstract and final. Null is a figment of the compiler similar Nothing, used as a bottom-type for all reference types. That is, Null is a sub-type of any other type that inherits from AnyRef. Its only value is the null reference, but there is no way to instantiate the Null class and magically get a null reference. It differs from Nothing in that it is inhabited by a single value: null.

Therefore, if you assign null to an identifier, Null will be inferred as its type if you don't hint otherwise.

scala> val a = null
a: Null = null