classOf[T]           相当于Java 里的   T.class
obj.isInstanceOf[T]  相当于Java 里的   obj instanceof T
obj.asInstanceOf[T]  相当于Java 里的   (T)obj


val c : Char = 97.asInstanceOf[Char]  
3.asInstanceOf[Long] 

"hello".isInstanceOf[String]  
true

"hello".isInstanceOf[Int]  
false

val list = List("a","b","c")
List[String] = List(a, b, c)

val seq = list.asInstanceOf[Seq[String]]  
Seq[String] = List(a, b, c)


classOf[String]  
Class[String] = class java.lang.String

classOf[Int]  
Class[Int] = int

注意类型擦除

List(1).isInstanceOf[List[String]]  
List(1).isInstanceOf[List[_]] 
返回TRUE
List(1)是List的实例