Scala Cookbook

11.7. Different Ways to Create and Update an Array

Problem

You want to create and optionally populate an Array.

Solution

There are many different ways to define and populate an Array. You can create an array with initial values, in which case Scala can determine the array type implicitly:

scala> val a = Array(1,2,3)
a: Array[Int] = Array(1, 2, 3)

scala> val fruits = Array("Apple", "Banana", "Orange")
fruits: Array[String] = Array(Apple, Banana, Orange)

If you don’t like the type Scala determines, you can assign it manually:

// scala makes this Array[Double]
scala> val x = Array(1, 2.0, 33D, 400L)
x: Array[Double] = Array(1.0, 2.0, 33.0, 400.0)

// manually override the type
scala> val x = Array[Number](1, 2.0, 33D, 400L)
x: Array[java.lang.Number] = Array(1, 2.0, 33.0, 400)

You can define an array with an initial size and type, and then populate it later:

// create an array with an initial size
val fruits = new Array[String](3)

// somewhere later in the code ...
fruits(0) = "Apple"
fruits(1) = "Banana"
fruits(2) = "Orange"

You can create a var reference to an array in a class, and then assign it later:

// this uses a null. don't do this in the real world
var fruits: Array[String] = _

// later ...
fruits = Array("apple", "banana")

The following examples show a handful of other ways to create and populate an Array:

scala> val x = Array.range(1, 10)
x: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9)

scala> val x = Array.range(0, 10, 2)
x: Array[Int] = Array(0, 2, 4, 6, 8)

scala> val x = Array.fill(3)("foo") ...