scala SBT 错误：java.lang.RuntimeException：未检测到主类
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SBT error: java.lang.RuntimeException: No main class detected
提问by derek
Update:
I need put libraryDependencies for using Actor in Scala.
更新：
我需要放置 libraryDependencies 才能在 Scala 中使用 Actor。
libraryDependencies <++= scalaVersion(v =>
Seq("org.scala-lang" % "scala-actors" % v)
)
when I ran "sbt run", I could successfully pass the compilation but then failed on run the code.
当我运行“sbt run”时，我可以成功通过编译，但在运行代码时失败。
Here is the error: java.lang.RuntimeException: No main class detected.
这是错误：java.lang.RuntimeException：未检测到主类。
The weird thing is when I do not use SBT, I can run it without any issue:
奇怪的是，当我不使用 SBT 时，我可以毫无问题地运行它：
>scalac actor.scala
>scala pingpong
Any idea why this happens?
知道为什么会这样吗？
I am using SBT 0.13.0 Scala version is 2.10.2
我使用的是 SBT 0.13.0 Scala 版本是 2.10.2
Thanks
谢谢
Deryk.
德里克。
Here is my code:
这是我的代码：
import scala.actors.Actor
import scala.actors.Actor._
case object Ping;
case object Pong;
case object Stop;
class Ping(count:Int, pong:Actor) extends Actor
{
def act()
{
var counter = count -1 ;
pong ! Ping;
loop
{
react
{
case Pong =>
if( (counter < count) && (counter > 0) ) {Console.println(counter+"->Ping: pong"); pong ! Ping; counter = counter -1;}
else {pong ! Stop;exit()}
}
}
}
}
class Pong extends Actor
{
def act()
{
loop
{
react
{
case Ping => {Console.println("Pong: Ping"); sender ! Pong;}
case Stop => {Console.println("Ping Pong Communication is done!");exit()}
}
}
}
}
object pingpong
{
def main(args: Array[String])
{
println(util.Properties.versionString)
val pong = new Pong
val ping = new Ping(5, pong)
ping.start
pong.start
}
}
采纳答案by derek
If you want to use Actor in Scala, you need include the library, as the following:
如果要在 Scala 中使用 Actor，则需要包含该库，如下所示：
libraryDependencies <++= scalaVersion(v =>
Seq("org.scala-lang" % "scala-actors" % v)
)
回答by Vidya
Try this in your build file:
在你的构建文件中试试这个：
mainClass in (Compile,run) := Some("pingpong")
回答by Przemek
I have this exception if I try to use class instead of object.
如果我尝试使用类而不是对象，则会出现此异常。
//class Foo extends App {
// print("No main class detected")
//}
object Foo extends App {
print("Hello World")
}
回答by Mike Addison
It's looking for an object. Try creating a simple clock.scala object file and re-running it:
它正在寻找一个对象。尝试创建一个简单的 clock.scala 对象文件并重新运行它：
object Clock {
def main(args: Array[String]) = println(new java.util.Date)
}
回答by Denys Lobur
You have to move your class which extends App to src/main/scalafolder. Otherwise you have to create mainmethod
您必须将扩展 App 的类移动到src/main/scala文件夹。否则你必须创建main方法
