HelloWorld With main() Method

• Open Scala program HelloWorld.scala

object HelloWorld {

  /**
   *  Entry point of program : equivalent of Java main method
   *  Parameter passed : 'scala.Array' of 'Predef.String'
   *  Property 'scala.Predef.String' eventually calls 'java.lang.String'
   *  Scala object 'scala.Predef' is a placeholder for mostly used Scala classes
   */
  def main(args: Array[String]): Unit = {

    /* Control flow : scala.Predef.println --> scala.Console.println --> java.io.PrintStream.println */
    println("Hello World")
  }
}

HelloWorld Without main Method

• Scala provides scala.App class to avoid main method

• Open Scala program HelloWorldWithoutMain.scala

object HelloWorldWithoutMain extends App {

  /* Control flow : scala.Predef.println --> scala.Console.println --> java.io.PrintStream.println */
  println("Hello World")
}

Input/Output in Scala

• To print the value on console you can use print : print("Hello World")

• To print the value on console in a new line you can use println println("Hello World")

• To print the formatted value use printf (like C) printf("Hello, %s! You are %d years old.\n", "John", 32)

• Read a line of input from the console with the readLinefunction.

• To read a specific value, use specific methods in Scala class scala.io.StdIn

  scala.io.StdIn.readInt
  scala.io.StdIn.readChar
  scala.io.StdIn.readBoolean
  scala.io.StdIn.readDouble
  scala.io.StdIn.readFloat
  scala.io.StdIn.readLong
  scala.io.StdIn.readShort

• With readLinemethod you can pass string before input: val name = scala.io.StdIn.readLine("Your name: ")

• These methods assume, next input line as a single number, without leading or trailing whitespace, else NumberFormatException occurs