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APPENDIX C: Introduction to Scala 427

operations that simulate additions, removals, or updates, but those operations will in each case
return a new collection and leave the old collection unchanged. Scala has a rich collections
library. The most commonly used collections are lists, sets, and maps, which are explained in the
following sections. You can find details on Scala’s collection library at http://docs.scala-lang.org/
overviews/collections/introduction.html.

Lists

Lists are immutable, which means the elements of a list cannot be changed by assignment. The type
of a list that has elements of type T is written as List[T], as shown here:

val numberList: List[Integer] = List(1, 2, 3)

Listing C-5 illustrates how to create and use an immutable list.

Listing C-5. Creating an Immutable List

val list = List(1, 2, 3, 2, 3)
println (list.head)
println(list.tail)
println(list.length)
println(list.max)
println(list.min)
println(list.sum)
println(list.sorted)
println(list.reverse)

head --- 1

tail --- List(2, 3, 2, 3)

length --- 5

max --- 3

min --- 1

sum --- 11

sorted --- List(1, 2, 2, 3, 3)

reverse--- List(3, 2, 3, 2, 1)

Scala defines only an immutable list. However, it also defines some mutable list types, such as
ArrayBuffer. Listing C-6 illustrates how to create a mutable list.

Listing C-6. Creating a Mutable List

import collection.mutable
val list = mutable.ArrayBuffer(1, 2, 3, 2, 3)
assert (list.length == 5)