Scala: How to convert a String to an Int (Integer)

Scala FAQ: How do I convert a String to Int in Scala?

Solution: Use ‘toInt’

If you need to convert a String to an Int in Scala, use the toInt method, which is available on String objects, like this:

scala> val i = "1".toInt
i: Int = 1

As you can see, I just cast the string "1" to an Int object using the toInt method, which is available to any String.

However, beware that this can fail with a NumberFormatException just like it does in Java:

scala> val i = "foo".toInt
java.lang.NumberFormatException: For input string: "foo"

so you’ll want to account for that in your code, such as with a Scala try/catch statement.

A Java-like String to Int conversion function

The following functions show a couple of ways you can handle the exception that can be thrown in the string to int conversion process. This first example shows the “Java” way to write a String to Int conversion function:

def toInt(s: String): Int = {
  try {
  } catch {
    case e: Exception => 0

That function returns the correct int value if the string can be converted to an int (such as "42"), and returns 0 if the string is something else, like the string "foo".

When I say that this function uses a Java-like approach, please note that I originally wrote this article before Java had the Optional type.

A Scala “String to Int” conversion function that uses Option

A more "Scala like" way to write a string to int conversion function looks like this:

def toInt(s: String): Option[Int] = {
  try {
  } catch {
    case e: Exception => None

This function returns a Some(Int) if the string is successfully converted to an int, and a None if the string could not be converted to an integer. This function is shown in the following REPL examples:

scala> val x = toInt("foo")
x: Option[Int] = None

scala> val x = toInt("10")
x: Option[Int] = Some(10)

As I wrote in my book about Scala and functional programming, you can also write a Scala toInt function that uses Try, Success, and Failure like this:

import scala.util.{Try, Success, Failure}
def makeInt(s: String): Try[Int] = Try(s.trim.toInt)

You can also return an Option like this:

import scala.util.control.Exception._
def makeInt(s: String): Option[Int] = allCatch.opt(s.toInt)

Please see my Scala Option/Some/None idiom tutorial for more ways to use these patterns, and to use the Option and Try results.

Note: As I hinted at above, the toInt method really isn't on the String class. It's actually contained in a class named StringOps, which is bound to the String class using an implicit conversion in Scala. I describe this a little more in my How to show String and StringOps methods in the Scala REPL examples.