Unable to access current millisecond time in scala using java.lang.System.currentTimeMillis();

Question

When I use below code in scala I get a runtime exception :

java.lang.NoSuchMethodError: main Exception in thread "main"

object Driver {

    def main(args:Array[String]) = {

      java.lang.System.currentTimeMillis();

    }

}

But when I remove java.lang.System.currentTimeMillis(); the main method is found.

Why is this ?

Answer 1

It's the equal sign!

That's causing Scala to infer the return type of main to be Long (Scala) / long (at the JVM level). When you remove it, it infers Unit / void. Likewise when you remove the call to currentTimeMillis.

Answer 2

def main(args:Array[String]): Unit = { is the exact signature for main(). Removing = seems also a solution, but less error-prone.