This one should be simple, but I can't figure it out myself.
I have Scala 2.9.1 installed on an Ubuntu 12.04 system.
The file is helloworld.scala:
object HelloWorld{
def main(args:Array[String]){
println("Hello, World!")
}
}
scalac helloworld works totally fine without issue. Then scala HelloWorld gives
Exception in thread "main" java.lang.RuntimeException: Cannot figure out how to run target: HelloWorld
at scala.sys.package$.error(package.scala:27)
at scala.tools.nsc.GenericRunnerCommand.scala$tools$nsc$GenericRunnerCommand$$guessHowToRun(GenericRunnerCommand.scala:38)
at scala.tools.nsc.GenericRunnerCommand$$anonfun$2.apply(GenericRunnerCommand.scala:48)
at scala.tools.nsc.GenericRunnerCommand$$anonfun$2.apply(GenericRunnerCommand.scala:48)
at scala.Option.getOrElse(Option.scala:108)
at scala.tools.nsc.GenericRunnerCommand.<init>(GenericRunnerCommand.scala:48)
at scala.tools.nsc.GenericRunnerCommand.<init>(GenericRunnerCommand.scala:17)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:33)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:89)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
I've seen this question several times on forums but the poster is usually just mixing the class name and the file name so they would be trying scala helloworld, this is not what I'm doing (right?) but I get the same error.
Edit
scala -classpath ./ HelloWorld works fine. So it's a classpath problem.
I tried this and got exactly the same. Then I cleared my classpath thus:
$ CLASSPATH=
and all worked.
Not what you asked, but since you have many dependencies, it would be better to use sbt and let it worry about classpaths.
I'm also using Ubuntu and testing with your example I can confirm that:
scala HelloWorld.scala
will run the file successfully as a Scala script. And:
scalac HelloWorld.scala
will create the class files.
But, running:
scala HelloWorld.class
will give the error you are getting.
However, if you are running
scala HelloWorld
in the directory that has the class file in it, then the program should execute without a problem.
Related
I'm following examples out of Programming in Scala book by Odersky and I'm unable to run a simple standalone scala file with scala hello.scala. When I do this, I get this error:
Error: Could not find or load main class hello.scala
Caused by: java.lang.ClassNotFoundException: hello.scala
I'm using scala3.
Here's a state of my file and commands I'm running.
If you follow the steps from the documentation you'll see that you need to compile your file before running it.
If you run:
scalac hello.scala
scala hello
You should get the result you want.
you might consider using the new (and excellent) tool from virtuslab called 'scala-cli': https://scala-cli.virtuslab.org/
This question already has answers here:
How to run jar generated by package (possibly with other jars under lib)?
(3 answers)
Closed 2 years ago.
after packaging and executing a Scala application (build.sbt with version 2.12.0, but in fact having 2.13.3 installed) with SBT (version 1.3.13), I get the following error:
Exception in thread "main" java.lang.NoSuchMethodError: scala.Predef$.wrapRefArray([Ljava/lang/Object;)Lscala/collection/mutable/WrappedArray;
at org.example.GreetWorld$.printMessage(GreetWorld.scala:5)
The source file GreetWorld.scala that caused the error looks like this:
package org.example
object GreetWorld {
def printMessage(theMessage:String):Unit = {
println(s"${theMessage} from me")
}
}
The main file that is invoking the file above looks like this:
package org.example
object HelloWorld {
def main(args: Array[String]) = {
GreetWorld.printMessage("Hello")
}
}
Does anybody know the root cause? At first I thought it has to do with the SBT shell picking Java 11, but even after changing my Windows' JAVA_HOME to Java 8, I still get the same error. Compiling and running it in SBT Shell works fine. Only the JAR execution fails.
The error is pretty simple. When you run package you create a JAR which only contains the classes corresponding to your source code, nothing more. And your code depends on the Scala stdlib, so if you try to run it with java - jar it will fail with a class path error.
You have 4 solutions:
Run the JAR using scala directly. However, you need to use the same major version it was used to compile.
Put the Scala library jar in the classpath when running. This is basically the same as above. Thus again, you have to use the same major version.
Create an uber jar that already has the Scala stdlib (as well as any other dependency) in it, using sbt-assembly.
Create a native distributable that will set up everything for you, using sbt-native-packager.
For local development and testing option 1 is usually the best one.
For simple projects option 3 is, IMHO, the simplest alternative.
And for very complex projects option 4 is very popular.
I've created a simple app that generates PageView for later Spark tasks.
I've only one scala file taht use a simple MAP
When created a package with SBT I run my class with command:
java -cp .\target\scala-2.10\pageviewstream_2.10-1.0.0.jar "clickstream.PageViewGenerator"
but I receive this error:
Exception in thread "main" java.lang.NoClassDefFoundError: scala/collection/immutable/Map
What I am doing wrong?
Many thanks in advance
Roberto
To run it correctly you need to add Scala runtime library into your class path:
java -cp $SCALA_HOME/lib/scala-library.jar;.\target\scala-2.10\pageviewstream_2.10-1.0.0.jar "clickstream.PageViewGenerator"
But .. you can run your application also as:
scala -classpath .\target\scala-2.10\pageviewstream_2.10-1.0.0.jar "clickstream.PageViewGenerator"
when you have scala already in PATH
or use directly sbt as:
sbt "runMain clickstream.PageViewGenerator"
when clickstream.PageViewGenerator is you only application it is enough to run:
sbt run
or when you are in sbt interactive mode just type:
> runMain clickstream.PageViewGenerator
or when it is only application in your project it is enough to run:
> run
I have my very first Scala program, which is as simple as:
object HelloWorld{
def main(args: Array[String]){
println("Hello world!")
}
}
I then try to compile it like so:
$ scalac HelloWorld.scala
And it compiles without any error messages. When however I try to run it like so:
$ scala HelloWorld
I get an error message:
No such file or class on classpath: HelloWorld
To implement this, I followed this tutorial and to solve the emerged error, I followed this suggestion. However,
$ scala objects.HelloWorld
also does not work. I know many people will now start heavily voting down my question and asking questions - have you ever tried to read some books on it (Yes, I did. I've read Horstman book for beginners, but it does not contain any information on compiling programs under Ubuntu). Still, I hope someone could help.
(This was a comment before, and I rephrased it to a response.)
You've done everything right, except for the last step: Use the java command instead of the scala command.
scala is the Scala REPL. No separate run command is required for Scala code, because it compiles to regular Java bytecode.
So try: java HelloWorld
For more complex programs that make use of the Scala library however, you need to include the Scala runtime library in the classpath. So, on the long run, it is beneficiary to use a tool like SBT, as pointed out by #roterl in the comments.
The answer saying that the scala command is just for the REPL is incorrect. You can see from the man page entry for scala (http://www.scala-lang.org/files/archive/nightly/docs-2.10.2/manual/html/scala.html) that it is intended to be used in the same way as the java command with the added flexibility that it will run the REPL, scripts, or compiled applications.
As some of the comments have indicated, this is almost certainly a path issue, which means that it requires more information to diagnose. One thing you can check is whether the scalac command produced a .class file in your current directory. If that is in the directory where you are running scala then the comments about needing . in your classpath are almost certainly correct.
Scala newb here (it's my 2nd day of using it). I want to get log4j logging working in my Scala script. The script and the results are below, any ideas as to what's going wrong?
[sean#ibmp2 pybackup]$ cat backup.scala
import org.apache.log4j._
val log = LogFactory.getLog()
log.info("started backup")
[sean#ibmp2 pybackup]$ scala -cp log4j-1.2.16.jar:. backup.scala
/home/sean/projects/personal/pybackup/backup.scala:1: error: value apache is not a member of package org
import org.apache.log4j._
^
one error found
I reproduce it under Windows: delimiter of '-classpath' must be ';' there (not ':'). Are you use cygwin or some sort of unix emulator?
But Scala script works anywhere without current dir in classpath. Try to use:
$ scala -cp log4j-1.2.16.jar backup.scala
JFI: LogFactory is a class of slf4j library (not log4j).
UPDATE
Another possible case: broken jar in classpath, maybe during download or something else. Scala interpreter does report only about unavailable member of the package.
$ echo "qwerty" > example.jar
$ scala -cp example.jar backup.scala
backup.scala:1: error: value apache is not a member of package org
...
Need to inspect content of the jar-file:
$ jar -tf log4j-1.2.16.jar
...
org/apache/log4j/Appender.class
...
Did you remember to put log4j.jar in your classpath?
Had Similar issue when started doing Scala Development using Eclipse, doing a clean build solved the problem.
Guess the Scala tools are not matured et.
Instead of using log4j directly, you might try using Configgy. It's the Scala Way™ to work with log4j, as well as configuration files. It also plays nicely with SBT and Maven.
I asked and answered this question myself, have a look:
Put it under src/main/resources/logback.xml. It will be copied to the right location when SBT is doing the artifact assembly.