Well,

When I evolve a UML model, I use the Rational Unified Process (RUP). It suggests that you're Analysis and Design models are essentially the same thing. It just evolves over time.

Initially the elements in this model are more abstract, and don't incorporate elements in the archicture description. Over time, as you apply the rules of the architecture (i.e. J2EE, and all the specifics of your particular application), <> classes will become JFrames, JSP, Servlets, etc. <> classes will become regular Java classes or session EJBs. Entity classes pretty much map directly to EJB Entity Beans.

The simple answer is you take an analysis level class, add appropriate data types and full operation signatures, have a Java component (i.e. Java <>) realize the class, and begin generating code (if you have a UML tool that can do it).

Some people like to maintain a separate analysis model. This is common in enterprise applications, and in larger orgzaniations, or in organizations that re-use artifacts at every level. There are some issues related to doing this, most noteably being able to keep the two in relative sync.