Java™ Application Development on Linux - Dator

282Chapter 12Analysis and Design: Seeking the ObjectsTo take our example, suppose we have the following list of CRC cardsafter such an open brainstorming session:• Database• Capital Account• Current Account• CEO• Computer• CFO• Director• Keyboard• ManagerWhere do you go from here? Let’s articulate a general principle.The first principle. If we could teach a programmer only one thing aboutsoftware design, it would be this idea: less is more. Or, to quote Antoine deSaint-Exupéry: “Perfection is achieved not when nothing can be added, butwhen nothing can be taken away.” Or, to put it yet another way, always usethe KISS 3 principle. The best object design is the smallest possible number ofclasses that model the real objects and meet all the requirements.You are seeking simplifying abstractions.First of all, all the objects that represent technologies or implementationdetails should be removed. In our list, this would include “Database,” “Computer,”and “Keyboard.” While it is likely that all three will be involved in thefinal product, they are not objects in the problem space. There is no theoreticalreason why an OOA session cannot produce a manual, noncomputer solution.It is a common tendency to leap from problem analysis directly to technicalsolutions. “We can write that in Java,” “We can store those in Oracle,” “Thatcould be an XML file.” Statements like these are to be avoided at this stage.Those are details about the implementation. You haven’t got a design toimplement yet!As we said, you are seeking simplifying abstractions. The next step, afterculling cards that do not represent real objects in the problem space, is togroup together the cards that have any attributes in common. If we look at our3. An acronym for: Keep It Simple, Stupid!