Listは一度宣言すると配列と違って二度と再代入出来ない。
$ scala
Welcome to Scala version 2.10.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_51).
Type in expressions to have them evaluated.
Type :help for more information.
scala> val list1 = List("Scala")
list1: List[String] = List(Scala)
scala> list1(0)
res0: String = Scala
scala> list1(0) ="Java"
<console>:9: error: value update is not a member of List[String]
list1(0) ="Java"
^
scala>
