Scala | String Interpolation

Last Updated : 26 Feb, 2019

String Interpolation refers to substitution of defined variables or expressions in a given String with respected values. String Interpolation provides an easy way to process String literals. To apply this feature of Scala, we must follow few rules:

String must be defined with starting character as s / f /raw.
Variables in the String must have ‘$’ as prefix.
Expressions must be enclosed within curly braces ({, }) and ‘$’ is added as prefix.

Syntax:

// x and y are defined
val str = s"Sum of $x and $y is ${x+y}"

Types of String Interpolator

s Interpolator: Within the String, we can access variables, object fields, functions calls, etc.

Example 1: variables and expressions:

// Scala program 
// for s interpolator 
  
// Creating object 
object GFG 
{  
    // Main method 
    def main(args:Array[String]) 
    { 
      
        val x = 20
        val y = 10
      
        // without s interpolator 
        val str1 = "Sum of $x and $y is ${x+y}"
  
        // with s interpolator 
        val str2 = s"Sum of $x and $y is ${x+y}"
      
        println("str1: "+str1) 
        println("str2: "+str2) 
    } 
} 

Output:

str1: Sum of $x and $y is ${x+y}
str2: Sum of 20 and 10 is 30

Example 2: function call

// Scala program 
// for s interpolator 
  
// Creating object 
object GFG 
{  
    // adding two numbers 
    def add(a:Int, b:Int):Int 
    =
    {  
        a+b  
    } 
      
    // Main method 
    def main(args:Array[String]) 
    { 
      
        val x = 20
        val y = 10
      
        // without s interpolator 
        val str1 = "Sum of $x and $y is ${add(x, y)}"
  
        // with s interpolator 
        val str2 = s"Sum of $x and $y is ${add(x, y)}"
      
        println("str1: " + str1) 
        println("str2: " + str2) 
    } 
} 

Output:

str1: Sum of $x and $y is ${add(x, y)}
str2: Sum of 20 and 10 is 30

f Interpolator: This interpolation helps in formatting numbers easily.

To understand how format specifiers work refer Format Specifiers.

Example 1: printing upto 2 decimal place:

// Scala program 
// for f interpolator 
  
// Creating object 
object GFG 
{  
    // Main method 
    def main(args:Array[String]) 
    { 
      
        val x = 20.6
      
        // without f interpolator 
        val str1 = "Value of x is $x%.2f"
  
        // with f interpolator 
        val str2 = f"Value of x is $x%.2f"
      
        println("str1: " + str1) 
        println("str2: " + str2) 
      
    } 
} 

Output:

str1: Value of x is $x%.2f
str2: Value of x is 20.60

Example 2: setting width in integers:

// Scala program 
// for f interpolator 
  
// Creating object 
object GFG 
{  
    // Main method 
    def main(args:Array[String]) 
    { 
      
        val x = 11
      
        // without f interpolator 
        val str1 = "Value of x is $x%04d"
  
        // with f interpolator 
        val str2 = f"Value of x is $x%04d"
      
        println(str1) 
        println(str2) 
    } 
} 

Output:

Value of x is $x%04d
Value of x is 0011

If we try to pass a Double value while formatting is done using %d specifier, compiler outputs an error. In case of %f specifier, passing Int is acceptable.

raw Interpolator: String Literal should start with ‘raw’. This interpolator treats escape sequences same as any other character in a String.
Example :printing escape sequence:

// Scala program 
// for raw interpolator 
  
// Creating object 
object GFG 
{  
    // Main method 
    def main(args:Array[String]) 
    { 
          
        // without raw interpolator 
        val str1 = "Hello\nWorld"
  
        // with raw interpolator 
        val str2 = raw"Hello\nWorld"
      
        println("str1: " + str1) 
        println("str2: " + str2) 
    } 
} 