Scala Strings

Data Types introduced string literals and basic s"..." interpolation. This page goes further: the other interpolators, the common StringOps methods you will use daily, mutable StringBuilder for building text in a loop, and regular expressions.

The Three Interpolators

Scala ships three string interpolators. All three start with a prefix letter right before the opening quote.

Prefix	Name	Purpose
`s"..."`	Standard	Substitutes `$identifier` and `${expression}`.
`f"..."`	Formatted	Same substitution, plus `printf`-style format specifiers like `%d`, `%.2f`.
`raw"..."`	Raw	Substitutes like `s"..."` but does not process escape sequences such as `\n`.

Example:

val name  = "Ana"
val price = 19.5

println(s"Hello, $name!")                 // Hello, Ana!
println(f"Total: $$${price}%.2f")         // Total: $19.50
println(raw"Line one\nLine two")          // Line one\nLine two  (no real newline)

Common StringOps Methods

Every String in Scala is a Java String enriched with dozens of extra methods via StringOps. You get the safety of an immutable value with a collection-like API on top.

Method	What it does
`.trim`	Removes leading and trailing whitespace.
`.split(sep)`	Splits into an `Array[String]` on a separator (regex-aware).
`.replace(a, b)`	Replaces every literal occurrence of `a` with `b`.
`.contains(sub)`	True if `sub` appears anywhere in the string.
`.toUpperCase` / `.toLowerCase`	Case conversion.
`.reverse`	Reverses the characters.
`.padTo(n, ch)`	Pads on the right with `ch` until length `n`.
`.stripMargin`	Strips leading whitespace and a leading `\|` from each line of a multiline string.
`.toIntOption`	Parses to `Option[Int]` instead of throwing — see Error Handling.

Example:

val messy = "  Scala, Kotlin, Java  "

val parts = messy.trim.split(",").map(_.trim)
println(parts.mkString(" | ")) // Scala | Kotlin | Java

println("42".toIntOption)      // Some(42)
println("nope".toIntOption)    // None

StringBuilder

A String is immutable, so concatenating one in a loop rebuilds a new string every iteration. For heavy text building, use the mutable StringBuilder and call .toString once at the end.

Example:

val sb = new StringBuilder()

for (i <- 1 to 5) {
  sb.append(i)
  if (i < 5) sb.append(", ")
}

println(sb.toString) // 1, 2, 3, 4, 5

Regular Expressions

A Regex is created from any string with .r, or from the dedicated r"..." interpolator. Regex objects support pattern matching directly, which reads naturally in a match expression.

Example:

val datePattern = raw"(\d{4})-(\d{2})-(\d{2})".r

"2026-09-29" match {
  case datePattern(year, month, day) =>
    println(s"Year=$year Month=$month Day=$day")
  case _ =>
    println("Not a date")
}

// findAllIn returns every match as an iterator
val words = raw"\w+".r.findAllIn("Scala is fun").toList
println(words) // List(Scala, is, fun)