Question

Possible Duplicate:
If an Int can't be null, what does null.asInstanceOf[Int] mean?

I tried the following in REPL:

scala> null.asInstanceOf[Int]
res12: Int = 0

scala> null.asInstanceOf[Float]
res13: Float = 0.0

scala> null.asInstanceOf[Double]
res14: Double = 0.0

It would expect a runtime exception (NPE or ClassCastException) in that case.
Could anybody explain why Scala casts null to zero?

Answer 1

It’s really strange, as it is not the behaviour expected according to the specification:

asInstanceOf[T] returns the null object itself if T conforms to
scala.AnyRef, and throws a NullPointerException otherwise.

— The Scala Language Specification, Version 2.9, p. 75.

And it’s a known bug that is closed but related to this one, which is open.