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Streams in Scala

By IncludeHelp Last updated : November 14, 2024

Scala Streams

Stream in Scala is a type of lazy val. It is a lazy val whose elements are evaluated only when they are used in the program. Lazy initialization is a feature of Scala that increases the performance of the program.

Syntax

val str = 1 #:: 2 #:: 3 #:: Stream.empty

Elements of a stream are created using #:: operator using Stream.empty at the end of initialization.

Program to show the creation of a stream

object myObject 
{ 
	def main(args: Array[String]): Unit = {
		val myStream =  2 #:: 4 #:: 6 #:: Stream.empty; 
		println("New Stream created...")
		println(myStream)
	} 
}

Output

New Stream created...
Stream(2, <not computed>)

Creating stream using stream.cons

You can create a stream using stream.cons. It will create an immutable stream and needs an import statement Scala.collection.immutable.Stream.cons.

import scala.collection.immutable.Stream.cons 

object myObject 
{ 
	def main(args: Array[String]): Unit = {
		val myStream: Stream[Int] = cons(2, cons(4, cons(6, Stream.empty)))
		println("New Stream created...")
		println(myStream)
	} 
}

Output

New Stream created...
Stream(2, <not computed>)

Accessing elements of the stream

In streams, take method is used to take/access elements.

Program to access elements using take method

import scala.collection.immutable.LazyList.cons

object myObject {
  def main(args: Array[String]): Unit = {
    val myStream: LazyList[Int] = cons(2, cons(4, cons(6, cons(9, LazyList.empty))))
    print("Accessing Stream: ")
    println(myStream)

    print("\nTake first 2 elements of stream: ")
    myStream.take(2).foreach(print)

    print("\n\nTake all elements from stream: ")
    myStream.take(5).foreach(print)
  }
}

Output

Accessing Stream : Stream(2, <not computed>)
Take first 2 elements of stream : 2, 4
Take all elements from stream : 2, 4, 6, 9

Creating an empty Stream

You can create an empty stream in Scala using Stream.empty.

object myObject 
{ 
    def main(args: Array[String]): Unit = {
        val myStream: Stream[Int] = Stream.empty[Int] 
        print("This is an empty Stream : ") 
        println(myStream)
    } 
} 

Output

This is an empty Stream : Stream()