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, although I do show the output of all the examples. This is mostly just a collection of examples that can be used as a Scala String reference page or cheat sheet.
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
Scala 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
Multiline Scala strings
Multiline strings in Scala 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"""
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")
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
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
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
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]
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"
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))
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