You can call a JAVA action from another JAVA action (in the execute method) as follows:
HashMap<String, Object> params = new HashMap<String, Object>(); Core.execute(this.getContext(), "Module.JavaActionName", params);
Where params is a HashMap with parameters that the JAVA action you call expect.
The other way is that you create a instance of the 'second' JAVA action class and call the execute function on the created object. But that's not advised because you pass the Core functionality of the Core.execute function.
I hope this helps you. If not, clarify your question.
If you run a java action in a microflow, the return value will be placed in variable. This variable can be used as parameter for the other java action call.