Akka启动时，报错：java.lang.NoClassDefFoundError: scala/Product$class

错误提示如下：

Connected to the target VM, address: '127.0.0.1:51983', transport: 'socket'
Exception in thread "main" java.lang.NoClassDefFoundError: scala/Product$class
    at akka.util.Timeout.<init>(Timeout.scala:13)
    at akka.actor.ActorSystem$Settings.<init>(ActorSystem.scala:170)
    at akka.actor.ActorSystemImpl.<init>(ActorSystem.scala:540)
    at akka.actor.ActorSystem$.apply(ActorSystem.scala:141)
    at akka.actor.ActorSystem$.apply(ActorSystem.scala:108)
    at com.m24.learn.akka.SysHelloActor$.start(AkkaDemo.scala:20)
    at com.m24.learn.akka.AkkaDemo$.main(AkkaDemo.scala:31)
    at com.m24.learn.akka.AkkaDemo.main(AkkaDemo.scala)
Caused by: java.lang.ClassNotFoundException: scala.Product$class
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:338)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 8 more
Disconnected from the target VM, address: '127.0.0.1:51983', transport: 'socket'

Process finished with exit code 1

原因：

akka需要和scala版本相对应

dependencies {
    compile group: 'org.scala-lang', name: 'scala-library', version: '2.12.6'
    compile "org.scala-lang:scala-compiler:2.12.6"
    compile "org.scala-lang:scala-reflect:2.12.6"
    compile "com.typesafe.akka:akka-actor_2.12:2.5.17"

    testCompile "junit:junit:4.11"
}