Scala Collections - Stream

Scala Stream is special list with lazy evaluation feature. In scala stream, elements are evaluated only when they are needed. Stream supports lazy computation and is performance savvy.

Declaring Stream Variables

The following is the syntax for declaring an Stream variable.

Syntax

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

Here, stream is declared as a stream of numbers. Here 1 is head of stream, 2, 3 are tail of stream. Stream.empty marks the end of the stream. Values can be retrived using take commands like the following −

Command

stream.take(2)

Processing Stream

Below is an example program of showing how to create, initialize and process Stream −

Example

import scala.collection.immutable.Stream
object Demo {
   def main(args: Array[String]) = {
      val stream = 1 #:: 2 #:: 3 #:: Stream.empty
      // print stream
      println(stream)
      // Print first two elements	
      stream.take(2).print
      println()
      // Create an empty stream
      val stream1: Stream[Int] = Stream.empty[Int]
      // Print element
      println(s"Stream: $stream1")
   }
}

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Command

\>scalac Demo.scala
\>scala Demo

Output

Stream(1, <not computed>)
1, 2
Stream: Stream()