How to run simple Scala class from terminal?

Question

I have the Scala program myTest.scala with the following content:

class Test {
    def hello() {
        println("Hello, world!")
    }
}

How can I execute it from the console? If I run scala myTest.scala in the terminal, it obviously cannot find the main method which I do not have. Is there any way to run it as scala Test.hello? Is it mandatory to use scalac to compile before running scala?

Answer 1

You need to first give your Object a main method. There are 2 ways to do this:

object HelloWorld {
 def main(args: Array[String]): Unit = {
   println("Hello, world!")
 }
}

or

object HelloWorld extends App {
   println("Hello, world!")
}

Once you have your object ready. You can compile your class in your terminal as below:

$ scalac HelloWorld.scala

and run the program.

$ scala HelloWorld

More on this here.

Answer 2

You can't run a class in Scala.

You need to define an object with a main method or that extends App

object Test extends App {
  println("Hello, world!")
}