Convert

A String contains a number like 20. But these are characters. To get an Int we must call a parsing method—we must convert the string.

Scala 3.3 provides many built-in methods to convert Strings, Ints, Lists and Arrays. We use these for the clearest, smallest code.

ToString

Here we convert an Int to a string. And then we convert that string into an Int again. We use the toString def (part of scala.Any) and the toInt def (part of StringLike).

object Program {
    def main(args: Array[String]): Unit = {
        val number = 123

        // Convert Int to String.
        val result = number.toString()
        if (result == "123") {
            println(result)
        }

        // Convert String back to Int.
        val original = result.toInt
        if (original == 123) {
            println(original)
        }
    }
}
123
123

ToArray

In Scala we usually use Lists to store and manipulate data. But Arrays are also available—these are somewhat harder to work with.

object Program {
    def main(args: Array[String]): Unit = {
        val colors = List("blue", "yellow", "red")

        // Convert list to array.
        val result = colors.toArray

        // Print list.
        println(colors)

        // Print length and elements of the array.
        println(result.length)
        result.foreach(println(_))
    }
}
List(blue, yellow, red)
3
blue
yellow
red

List to string, StringBuilder

With addString (a method on List) we can add all list elements to a StringBuilder. The result by default has no separators.

object Program {
    def main(args: Array[String]): Unit = {
        val animals = List("cat", "bird", "fish")

        // Create a StringBuilder to store all list element values.
        val builder1 = new StringBuilder()
        // Call addString to add all strings with no separator.
        animals.addString(builder1)
        val result1 = builder1.toString()
        println(result1)

        // Use a separator with addString.
        // ... Converts a list to a string.
        val builder2 = new StringBuilder()
        animals.addString(builder2, "; ")
        val result2 = builder2.toString()
        println(result2)
    }
}
catbirdfish
cat; bird; fish

Range, list

In Scala we find a toList function that can convert many iterable collections into a list. This is part of scala.collection.TraversableOnce.

object Program {
    def main(args: Array[String]): Unit = {
        // Create a range from 10 to 20.
        // ... Step is 3 after each element.
        val range = 10.to(20).by(3)
        println(range)

        // Use toList to convert a range to a list.
        val list = range.toList
        println(list)
    }
}
inexact Range 10 to 20 by 3
List(10, 13, 16, 19)

Vector, List

The Vector has different performance characteristics than a List: it can be added to and updated faster. We sometimes have a Vector, but need a List.

object Program {
    def main(args: Array[String]): Unit = {
        // An empty vector.
        val vector = scala.collection.immutable.Vector.empty
        println(vector)

        // Add 2 new values at the end.
        val vector2 = vector :+ 1 :+ 5
        println(vector2)

        // Convert Vector to a List.
        val result = vector2.toList
        println(result)
    }
}
Vector()
Vector(1, 5)
List(1, 5)

StringLike

In Scala we find the StringLike type. This helps us convert and modify strings. As in Java, converting strings makes copies of existing strings.

Usually it is best to use the data type that is closest to the meaning of a value. So a string that means 100 is less effective than an Int of 100.