Scala List FAQ: How do I add elements to a Scala List?
This is actually a trick question, because you can't add elements to a ScalaList; it's an immutable data structure, like a Java String.
Prepending elements to Scala Lists
One thing you can do when working with a Scala List is to create a newList from an existing List. This sort of thing is done often in functional programming, and the general approach looks like this:
scala> val p1 = List("Kim")
p1: List[String] = List(Kim)
scala> val p2 = "Julia" :: p1
p2: List[String] = List(Julia, Kim)
scala> val p3 = "Judi" :: p2
p3: List[String] = List(Judi, Julia, Kim)
Those examples show how to create a series of lists. The initial list namedp1 contains one string, then p2 contains two strings, and finally p3 contains three strings.
While that approach looks cumbersome in a small example, it makes sense in larger, real-world code. You can see more/better examples of this approach in my tutorial titled, Scala List class examples.
Use a ListBuffer when you want a "List" you can modify
If you want to use a Scala sequence that has many characteristics of a Listand is also mutable (you can add and remove elements in it), use theListBuffer class instead, like this:
import scala.collection.mutable.ListBuffer var fruits = new ListBuffer[String]() fruits += "Apple" fruits += "Banana" fruits += "Orange"
Then convert it to a List if/when you need to:
val fruitsList = fruits.toList
Scala REPL example
Here's what this List and ListBuffer example looks like using the Scala command line (REPL):
scala> import scala.collection.mutable.ListBuffer import scala.collection.mutable.ListBuffer scala> var fruits = new ListBuffer[String]() fruits: scala.collection.mutable.ListBuffer[String] = ListBuffer() scala> fruits += "Apple" res0: scala.collection.mutable.ListBuffer[String] = ListBuffer(Apple) scala> fruits += "Banana" res1: scala.collection.mutable.ListBuffer[String] = ListBuffer(Apple, Banana) scala> fruits += "Orange" res2: scala.collection.mutable.ListBuffer[String] = ListBuffer(Apple, Banana, Orange) scala> val fruitsList = fruits.toList fruitsList: List[String] = List(Apple, Banana, Orange)
More functional ways to work with Scala lists
Depending on your needs, there are other, "more functional" ways to work with Scala lists, and I work through some of those in my Scala List examples. But for my needs today, I just wanted to work with a Scala Listlike I'd work with a Java List (ArrayList, LinkedList), and this approach suits me.