Another option is any classless java file is just a class with the same name as the file implementing Runnable.

E.g. Foo.java

   println("foo")

Becomes:

   class Foo implements Runnable {
     void run() {
       System.out.println("foo");
     }
   }

Then running java Foo.java instead just stubs a main() that looks like:

   class Main {
     void main() {
       new Foo().run();
     }
   }