Can java run a compiled scala code?

Question

Can command java run a compiled scala code? If so, why do we have an exclusive command scala ?

Answer 1

You can run byte code generated by Scala if you include all necessary runtime libs for Scala (scala-library.jar, scala-swing.jar ...) in the classpath. The scala command does this automatically, and supports Scala specific command line arguments.

Answer 2

Yes, it can. Scala is compiled down to Java bytecode. But remember that it depends on the Scala runtime classes, so you need to still have Scala's jar files on the classpath.

If so, why do we have an exclusive command scala?

Convenience wrapper.

Answer 3

Scala is designed to integrate easily with applications that run on modern virtual machines, primarily the Java virtual machine (JVM). The main Scala compiler, scalac, generates Java class files that can be run on the JVM. -> http://www.artima.com/scalazine/articles/steps.html

As long as you have installed the scala runtime you should be fine: compile classes with scalac and run them with java .

Answer 4

Just want to add my own answer as additional value for the future readers:

scala, if run without parameter, will run an interactive shell

scala, if run with a text file name as parameter, will regard the file as a scala script

those two can't be done using java

Answer 5

If you look closely, the scala command is simply a bash helper-script which summarize to the below command:

$cat /usr/local/Cellar/scala@2.11/2.11.12_1/libexec/bin/scala

execCommand \
  "${JAVACMD:=java}" \
  $JAVA_OPTS \
  "${java_args[@]}" \
  "${classpath_args[@]}" \
  -Dscala.home="$SCALA_HOME" \
  $OVERRIDE_USEJAVACP \
  "$EMACS_OPT" \
  $WINDOWS_OPT \
   scala.tools.nsc.MainGenericRunner  "$@"

There are 2 things required to run a .class file compiled using scalac ( the scala compiler) using the java command.

1. We need to include the scala-library.jar and the location of the .class file in the classpath . To find the location of scala-library.jar , please execute the below:

   which scala /usr/local/opt/scala@2.11/bin/scala

   In my case the scala-*.jar files are in : /usr/local/Cellar/scala@2.11/2.11.12_1/idea/lib on Mac

2. The location of the Main2.class file which is in /training/example1/scala .

So, to execute the program we could use the below command:

java -cp /usr/local/Cellar/scala@2.11/2.11.12_1/idea/lib/scala-library.jar:/training/example1/scala/ Main2

EDIT-1: If you are using windows, please use semicolon(;) as the separator in java classpath command.