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>