Scala · Lesson 1 · On the house

Hello Scala

object, def main, println, run basics. Lesson 1 is free — on the house.

Lessons · Scala · Lesson 1 of 10 · On the house

Hello Scala

object, def main, println, run basics.

Illustration for Scala — Lesson 1 is on the house.

A classic Scala JVM entry lives in a singleton object with def main(args: Array[String]): Unit. The object name is what you run after compiling.

println writes a line to standard output and adds a newline. print exists too but omits the trailing newline — demos almost always use println.

Line comments start with //. Block comments use /* ... */. Scala is case-sensitive: Println is not println.

Compile a single file with scalac Hello.scala, then run with scala Hello (the object name). With sbt, sbt run finds the main entry in the project.

Misses: writing public static void main (Java), using fun main (Kotlin), or forgetting args: Array[String] on the classic main signature.

hello

object Hello {
  def main(args: Array[String]): Unit = {
    println("hello")
  }
}

Match this when you type.

Quiz

Where does a classic Scala JVM entry live?

Inside an object with def main(args: Array[String]): Unit
Inside a package object named Main only
As a top-level print without any def
Inside a trait with fun main only

Quiz

Which call writes a line with a trailing newline?

console.log without parentheses
puts(...)
println(...)
echo(...)

Quiz

How do you compile then run a single-file Hello object?

scalac Hello.scala then scala Hello
kotlinc then kotlin Hello
javac Hello.scala then java Hello
python Hello.scala

Quiz

Is Scala case-sensitive?

Only for numbers
Only inside strings
Yes — Println is not println
No — identifiers ignore case

Check

Match the still for: Hello Scala.

Open-book: the answers are on this page. Pass every quiz and check (5) to mark the lesson done. This visit: 0/5.