I want to make a method that adds a Plan to a Runway, and a Runway to a Plan (their relation is bidirectional in my design), in my PlanDao and RunwayDao interfaces. Both classes have Lists to hold objects of the other class. When I create a new Runway, for example, it seems I can't do so without deciding on an implementation of List<Plan> (like ArrayList) and setting the list to a new instance of it, otherwise I get a nullpointer error when I try to add the Plan to it. Would it be bad practice to just go ahead and do this, or is there a way to allow Hibernate to do this. 

Also, is the policy of accepting late work with 10% penalty for 1 day late and 25% penalty for 2 days late apply to this assignment? I still want to get this done.