Main method in Scala

Question

I wrote a Scala class and defined the main() method in it. It compiled, but when I ran it, I got NoSuchMethodError:main. In all the scala examples

Answer 1

As Eugene said in a comment, there are no static methods in Scala. But watch this:

$ cat Echo.scala
object Echo {
  def main( args:Array[String] ):Unit = args foreach println
}

$ scalac Echo.scala

$ javap Echo\$.class
Compiled from "Echo.scala"
public final class Echo$ {
  public static final Echo$ MODULE$;
  public static {};
  public void main(java.lang.String[]);
}

$ javap Echo.class
Compiled from "Echo.scala"
public final class Echo {
  public static void main(java.lang.String[]);
}

Note that the classfile for the Echo class (not Echo$, the object) does indeed have a public static void main method. Scala generates static methods for methods defined in objects for compatibility with Java.

However, I consider creating a main method in a Scala program an anachronism. Use the App trait instead; it's cleaner:

object Echo extends App {
  args foreach println
}