Scala Tutorial - Scala Variable Declarations

Scala allows you to decide whether a variable is immutable (read-only) or not (read-write) when you declare it.

An immutable "variable" is declared with the keyword val:

val array: Array[String] = new Array(5)

Example

Array elements themselves are mutable, so the elements can be modified:

object Main {
  def main(args: Array[String]) {

     val array: Array[String] = new Array(5) 
     array = new Array(2) 
     array(0) = "Hello" 
     println(array )
  }
}

Note

A val must be initialized when it is declared.

Mutable variable

A mutable variable is declared with the keyword var and it must also be initialized immediately.

object Main {
  def main(args: Array[String]) {

     var stockPrice: Double = 100.0 
     stockPrice = 200.0 
     println(stockPrice);
  }
}

Example 2

The following code defines a Person class with immutable first and last names, but a mutable age.

class Person(val name: String, var age: Int) 

object Main {
  def main(args: Array[String]) {

     
     val p = new Person("Dean Wampler", 29) 
     println(p.name)
     println(p.age )
     p.age = 30
     println(p.age )

  }
}