I agree that this not yet the way it should be. This `rxjava-scala-java` project only contains `MovieLibUsage.java`, which illustrates that Scala code using Scala Observables can be used from Java with Java Observables. 
`MovieLibUsage.java` should reside somewhere in `rxjava-scala/src/examples`, and should be compiled by the Java compiler, but only **after** the Scala compiler has compiled `MovieLib.scala`. Since I have no experience with gradle, the only way I could solve this was to make a seperate project for `MovieLibUsage.java` which depends on the project containing `MovieLib.scala`.
Another solution that I found would be to instruct the *Scala* compiler to compile `MovieLibUsage.java`, too, but I don't like this solution, because I'd like to illustrate with this example that Java code depending on Scala libraries using Scala Observables can be built using the *Java* compiler having Scala-generated class files on the classpath.
I'd be very happy if you could set up the gradle build such that this works.