how to use asInstanceOf properly in Scala

I have been playing with basic Scala data types. I noticed that the scala.Any class defines the method asInstanceOf[T0]: T0 from here The API has it that it can "Cast the receiver object to be of type T0". Using this method as a starting point, I wanted to investigate casting in Scala. Also, I looked up stackoverflow for other questions on this topic and I came up with this With this information in hand, I wrote up a silly program.

         package com.att.scala
         import com.att.scala.Sheltie

         object Casting {

             //def foo(x: String){ 
             def foo(x: Int) {
              println("x is " + x)
             //if(x.isInstanceOf[String])
              if(x.isInstanceOf[Int])
                 println("Int x is " + x)
                //println("String x is " + x)
             }

            def entry() {
               //val double: Any = 123.123
               val double: Double = 123.23
               val int = double.asInstanceOf[Int] //exception expected here
               //val str: String = "123"
               foo(int) 
             }

         }

My goal is to understand what happens (and why) in the following cases: 1) casting from an Any type to an Int. 2) casting from Double type to an Int 3) casting from String to Int

1. In the first case, I got a run time ClasscastException as below, when I ran the program as - com.att.scala.Casting.entry. The exception is shown below:

   java.lang.ClassCastException: java.lang.Double cannot be cast to java.lang.Integer at scala.runtime.BoxesRunTime.unboxToInt(Unknown Source) at com.att.scala.Casting$.entry(Casting.scala:17)

2. In the second case, I get the follow