For those times when you want to isolate the Java and give it a quick test..
Can you run non-Android Java projects in Android studio as in Eclipse?
Tested on Android Studio 0.8.6 - 2.1
Using this method you can have Java modules and Android modules in the same project and also have the ability to compile and run Java modules as stand alone Java projects.
Now if you click run, this should compile and run your Java module.
My usage case: My Android app relies on some precomputed files to function. These precomputed files are generated by some Java code. Since these two things go hand in hand, it makes the most sense to have both of these modules in the same project.