A collection of 100+ Scala String examples

This page contains a collection of over 100 Scala String examples, including string functions, format specifiers, and more. I don’t provide too many details about how things work in these examples; this is mostly just a collection of examples that can be used as a Scala String reference page or cheat sheet. (I do show the output of most examples.)

 

 

 

Back to top

The style used in this lesson

First, here are some basic uses of the Scala String class to help demonstrate the style I’ll use in this lesson:

val hello = "Hello"

hello(0)                    // "H"
hello(1)                    // "e"
hello.length                // 5
hello.foreach(print)        // Hello
hello.drop(2)               // llo
hello.take(2)               // He
hello.take(2).toLowerCase   // he

As shown, I’ll demonstrate how to call a method and then show its result after the //. In the real world you’d assign that result to a variable, like this:

val len = hello.length
Back to top

String equality

You test string equality with ==:

val a = "foo"
val b = "foo"
val c = "bar"
a == b       // true
a == c       // false
a == null    // false
null == a    // false
Back to top

Multiline strings

Multiline strings are created with triple-quotes:

val foo = """This is
    a multiline
    String"""

val speech = """Four score and
               |seven years ago""".stripMargin

val speech = """Four score and
               #seven years ago""".stripMargin('#')

Those last two examples both result in this:

Four score and
seven years ago

Here’s another example:

val speech = """Four score and
               |seven years ago
               |our fathers...""".stripMargin.replaceAll("\n", " ")

When it’s executed, speech contains this string:

Four score and seven years ago our fathers...

You can also use single- and double-quotes in multiline strings:

val s = """This is known as a
"multiline" string
or 'heredoc' syntax"""
Back to top

String interpolation/substitution

Regarding Scala string substitution/interpolation, there are three built-in interpolators:

  • s

  • f

  • raw

Examples of String substitution/interpolation:

val name = "Joe"
val age = 42
val weight = 180.5

// `s` prints "Hello, Joe"
println(s"Hello, $name")

// `f` prints "Joe is 42 years old, and weighs 180.5 pounds."
println(f"$name is $age years old, and weighs $weight%.1f pounds.")

// `raw` interpolator prints "foo\nbar"
println(raw"foo\nbar")
Back to top

Treating a String as a Seq[Char]

A String is a sequence of Char, as these examples demonstrate:

scala> for (c <- "hello") yield c.toUpper
res0: String = HELLO

scala> "hello".foreach(println)
h
e
l
l
o

scala> "hello".getBytes.foreach(println)
104
101
108
108
111
Back to top

Using map and for

You can write your own functions to operate on a string. First, create a function that takes a Char and returns whatever type you want it to return:

// a method that takes a Char and returns a Char
def toLower(c: Char): Char = (c.toByte+32).toChar

Then you can use that function with map or for/yield:

scala> "HELLO".map(toLower)
val res0: String = hello

scala> for (c <- "HELLO") yield toLower(c)
val res1: String = hello

A function that takes a Char as input and returns Unit can be used with foreach:

scala> def printIt(c: Char): Unit =  println(c)
def printIt(c: Char): Unit

scala> "HAL".foreach(c => printIt(c))
H
A
L

scala> "HAL".foreach(printIt)
H
A
L
Back to top

Regular expressions

Add .r to the end of a string to create a regular expression:

// create a regex with '.r'
val numPattern = "[0-9]+".r                     // Regex = [0-9]+

// use the regex on `address`
val address = "123 Main Street"                 // "123 Main Street"
val match1 = numPattern.findFirstIn(address)    // Some(123)

You can also use the Regex class:

// create a regex with Regex class
import scala.util.matching.Regex
val numPattern = new Regex("[0-9]+")                  // Regex = [0-9]+ 222
val address = "123 Main Street Unit 639"              // "123 Main Street Unit 639"

// `findAllIn` returns an iterator
val matches = numPattern.findAllIn(address)           // non-empty iterator

// force the result to a sequence
val matches = numPattern.findAllIn(address).toSeq     // Stream(123, ?)
val matches = numPattern.findAllIn(address).toArray   // Array(123, 639)
val matches = numPattern.findAllIn(address).toList    // List(123, 639)

These examples show how to replace string content using regular expressions:

val regex = "[0-9]".r                        // Regex = [0-9]
regex.replaceAllIn("123 Main Street", "x")   // "xxx Main Street"

"123 Main Street".replaceAll("[0-9]", "x")   // "xxx Main Street"
"Hello world".replaceFirst("l", "e")         // "Heelo world"
"99 Luft Balloons".replaceAll("9", "1")      // "11 Luft Balloons"
"99 Luft Balloons".replaceFirst("9", "1")    // "19 Luft Balloons"

These examples show how to extract the parts of a string you want with regular expression groups:

// create a regex
scala> val pattern = "([A-Za-z]+) (\\d+), (\\d+)".r
pattern: scala.util.matching.Regex = ([A-Za-z]+) (\d+), (\d+)

// apply the regex to a string
scala> val pattern(month, day, year) = "June 22, 2018"
month: String = June
day: String = 22
year: String = 2018
Back to top

Transforming arrays to a String

These example demonstrate how to transform an array to a string using mkString:

val a = Array(1,2,3)
a.mkString                  // "123"
a.mkString(",")             // "1,2,3"
a.mkString(" ")             // "1 2 3"
a.mkString("(", ",", ")")   // "(1,2,3)"

This example shows how to use a prefix, suffix, and separator with mkString:

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

scala> numbers.mkString("[", ",", "]")
res0: String = [1,2,3]
Back to top

distinct, intersect, and diff

These examples demonstrate the distinct, intersect, and diff methods:

// distinct
"hello world".distinct   // "helo wrd"

// intersect
val a = "Hello"
val b = "World"
a intersect b            // "lo"
b intersect a            // "ol"

// diff
val a = "Four score and six years ago"
val b = "Four score and seven years ago"
a diff b                 // "ix"
b diff a                 // "vene"
Back to top

Many String method examples

Finally, here’s a large collection of examples of string methods. First, you’ll need a few sample strings to work with:

val fbb = "foo bar baz"
val foo = "foo"

Here are examples of most of the methods available to a String:

foo * 3                          // foofoofoo

fbb.capitalize                   // Foo bar baz
fbb.collect{case c > 'b' => c}   // TODO takes a partial function

// returns an Int indicating if `this` is greater than `that`
fbb.compare("doo")              // 2   (this > that)
fbb.compare(fbb)                // 0   (this == that)
fbb.compare("goo")              // -1  (this < that)
fbb.compareTo("doo")            // 2   (this > that)
fbb.compareTo(fbb)              // 0   (this == that)
fbb.compareTo("goo")            // -1  (this < that)

fbb.compareToIgnoreCase("doo")          // 2   (this > that)
fbb.compareToIgnoreCase("FOO BAR BAZ")  // 0   (this == that)
fbb.compareToIgnoreCase("goo")          // -1  (this < that)

fbb.count(_ == 'a')              // 2
fbb.diff("foo")                  // " bar baz"
fbb.distinct                     // fo barz
fbb.drop(4)                      // bar baz
fbb.dropRight(2)                 // foo bar b
fbb.dropWhile(_ != ' ')          // " bar baz"
fbb.endsWith("baz")              // true
fbb.filter(_ != 'a')             // foo br bz

fbb.foldLeft("")(_.toUpperCase + _.toLower)   // FOO BAR BAz
fbb.fold                         // TODO

fbb.foreach(println(_))          // prints one character per line
fbb.foreach(println)             // prints one character per line

// use the interpolators instead of this
String.format("Hi, %s", "world") // "Hi, world"

fbb.getBytes.foreach(println)    // prints the byte value of each character, one value per line
fbb.head                         // f
fbb.headOption                   // Some(f)
fbb.indexOf('a')                 // 5
fbb.isEmpty                      // false
fbb.lastIndexOf('o')             // 2
fbb.length                       // 11
fbb.map(_.toUpper)               // FOO BAR BAZ
fbb.map(_.byteValue)             // Vector(102, 111, 111, 32, 98, 97, 114, 32, 98, 97, 122)
fbb.min                          // " "
fbb.mkString(",")                // f,o,o, ,b,a,r, ,b,a,z
fbb.mkString("->", ",", "<-")    // ->f,o,o, ,b,a,r, ,b,a,z<-
fbb.nonEmpty                     // true
fbb.par                          // a parallel array, ParArray(f, o, o,  , b, a, r,  , b, a, z)
fbb.partition(_ > 'e')           // (foorz, " ba ba")  // a Tuple2

fbb.reduce                       // TODO

fbb.replace('o', 'x')            // fxx bar baz
fbb.replace("o", "x")            // fxx bar baz
fbb.replaceAll("o", "x")         // fxx bar baz
fbb.replaceFirst("o", "x")       // fxo bar baz
fbb.reverse                      // zab rab oof
fbb.size                         // 11
fbb.slice(0,5)                   // foo b
fbb.slice(2,9)                   // o bar b

// NOTE: `sortBy` is complicated, this is a simple example
fbb.sortBy(c => c)               // "  aabbfoorz"

fbb.sortWith(_ < _)              // "  aabbfoorz"
fbb.sortWith(_ > _)              // "zroofbbaa  "
fbb.sorted                       // "  aabbfoorz"

fbb.span(_ != 'a')               // ("foo b", "ar baz")
fbb.split(" ")                   // Array(foo, bar, baz)
fbb.splitAt(3)                   // (foo," bar baz")

fbb.substring(0,3)               // "foo"
fbb.substring(0,4)               // "foo "
fbb.substring(1,5)               // "oo b"
fbb.substring(1,6)               // "oo ba"
fbb.substring(0, fbb.length-1)   // "foo bar ba"
fbb.substring(0, fbb.length)     // "foo bar baz"

fbb.tail                         // oo bar baz
fbb.take(3)                      // foo
fbb.takeRight(3)                 // baz
fbb.takeWhile(_ != 'r')          // foo ba
fbb.toArray                      // Array(f, o, o,  , b, a, r,  , b, a, z)
fbb.toBuffer                     // ArrayBuffer(f, o, o,  , b, a, r,  , b, a, z)
fbb.toList                       // List(f, o, o,  , b, a, r,  , b, a, z)
fbb.toSet                        // Set(f, a,  , b, r, o, z)
fbb.toStream                     // Stream[Char] = Stream(f, ?)
fbb.toLowerCase                  // foo bar baz
fbb.toUpperCase                  // FOO BAR BAZ
fbb.toVector                     // Vector(f, o, o,  , b, a, r,  , b, a, z)
fbb.trim                         // "foo bar baz"
fbb.view                         // SeqView[Char,String] = SeqView(...)

(Note that a String isn’t a great example for some of those methods.)

zip and zipWithIndex require a little more room for output, so I show them here separately:

fbb.zip(0 to 10)
// results in: Vector((f,10), (o,11), (o,12), ( ,13), (b,14),
                      (a,15), (r,16), ( ,17), (b,18), (a,19), (z,20))

fbb.zipWithIndex
// results in: Vector((f,0), (o,1), (o,2), ( ,3), (b,4), (a,5),
                      (r,6), ( ,7), (b,8), (a,9), (z,10))
Back to top