TheApp trait can be used to quickly turn objects into executable programs. Here is an example:

object Main extends App {  Console.println("Hello World: " + (args mkString ", "))}

No explicitmain method is needed. Instead, the whole class body becomes the “main method”.

args returns the current command line arguments as an array.

Caveats

It should be noted that this trait is implemented using theDelayedInit functionality, which means that fields of the object will not have been initialized before the main method has been executed.

Future versions of this trait will no longer extendDelayedInit.

In Scala 3, theDelayedInit feature was dropped.App exists only in a limited form that also does not support command line arguments and will be deprecated in the future.

@main methods are the recommended scheme to generate programs that can be invoked from the command line in Scala 3.

@main def runMyProgram(args: String*): Unit = {  // your program here}

If programs need to cross-build between Scala 2 and Scala 3, it is recommended to use an explicitmain method:

object Main {  def main(args: Array[String]): Unit = {    // your program here  }}