I am very new to Scala and too rusty in Java to consider myself anything other than a complete newbie. So I take easy steps to learn it.
When I looked at the actors, I tried a few things, but came across numerous NoClassDefFound errors. Ultimately, I decided to take an example of a book and build on top of it, instead of debugging my first attempt. Surprise: book examples do not work properly!
Here is an example from O'Reilly Scala programming:
import scala.actors.Actor class Redford extends Actor { def act() { println("A lot of what acting is, is paying attention.") } } val robert = new Redford robert.start
He suggested, when it was executed, to print a quote from Redford. However, when I run it, nothing happens, I return to the command line:
D:\prog\scala-2.8.1.final\pierric>scala testactors.scala D:\prog\scala-2.8.1.final\pierric>
Another example is seven programming languages in seven weeks. This is so (I just changed the lines from laziness):
import scala.actors._ import scala.actors.Actor._ case object Poke; case object Feed; class Kid() extends Actor { def act() { loop { react { case Poke => { println("Ow") println("Quit it") } case Feed => { println("gurgle") println("burp") } } } } } var bart = new Kid().start var lisa = new Kid().start println("starting") bart ! Poke lisa ! Poke bart ! Feed lisa ! Feed
This time, he should return a randomly ordered sequence of "ow quit it" and "gurgle burp". However, when I run it:
D:\prog\scala-2.8.1.final\pierric>scala testkids.scala starting D:\prog\scala-2.8.1.final\pierric>
Now one more funny thing. If I add a simple println line at the beginning of my action, follow these steps:
class Kid() extends Actor { def act() { println("Kid initializing") loop { react { ...
Then I get most of the time:
D:\prog\scala-2.8.1.final\pierric>scala testkids.scala starting Kid initializing Kid initializing D:\prog\scala-2.8.1.final\pierric>
But sometimes also:
starting Kid initializing Kid initializing scala.actors.Actor$$anon$1@5a9de6 : caught java.lang.NoClassDefFoundError: Main$$anon$1$Fee java.lang.NoClassDefFoundError: Main$$anon$1$Feed$ at Main$$anon$1.Main$$anon$$Feed(testkids.scala:5) at Main$$anon$1$$anonfun$1.apply$mcV$sp(testkids.scala:31) at scala.actors.Actor$$anon$1.act(Actor.scala:135) at scala.actors.Reactor$$anonfun$dostart$1.apply(Reactor.scala:222) at scala.actors.Reactor$$anonfun$dostart$1.apply(Reactor.scala:222) at scala.actors.ReactorTask.run(ReactorTask.scala:36) at scala.concurrent.forkjoin.ForkJoinPool$AdaptedRunnable.exec(ForkJoinPool.java:6 at scala.concurrent.forkjoin.ForkJoinTask.quietlyExec(ForkJoinTask.java:422) at scala.concurrent.forkjoin.ForkJoinWorkerThread.mainLoop(ForkJoinWorkerThread.ja at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:32 Caused by: java.lang.ClassNotFoundException: Main$$anon$1$Feed$ at java.net.URLClassLoader$1.run(Unknown Source)
So here I am, ignorant ... as examples "from a book", actually from two books! and don't seem to work. I tried on two different machines, which apparently have different JVMs. In both cases, I ran scala 2.8.1.final. On one machine 32-bit Windows XP runs, the other on 64-bit Windows 7. I did not find anything related to this problem with googling ...
Thanks in advance to everyone who can shed light on this!
Pierric.