How do you design object oriented projects?

architecture oop class-design
Victor picture Victor · Jul 9, 2009 · Viewed 98.5k times · Source

I'm working on a large project (for me) which will have many classes and will need to be extensible, but I'm not sure how to plan out my program and how the classes need to interact.

I took an OOD course a few semesters back and learned a lot from it; like writing UML, and translating requirements documents into objects and classes. We learned sequence diagrams too but somehow I missed the lecture or something, they didn't really stick with me.

With previous projects I've tried using methods I learned from the course but usually end up with code that as soon as I can say "yeah that looks something like what I had in mind" i have no desire to dig through the muck to add new features.

I've got a copy of Steve McConnell's Code Complete which I continually hear is amazing, here and elsewhere. I read the chapter on design and didn't seem to come out with the information I'm looking for. I know he says that it's not a cut and dried process, that it's mostly based on heuristics, but I can't seem to take all his information and apply it to my projects.

So what are things you do during the high level design phase (before you begin programming) to determine what are the classes you need (especially ones not based on any 'real world objects') and how will they interact with each other?

Specifically I'm interested in what are the methods you use? What is the process you follow that usually yeilds a good, clean design that will closely represent the final product?

Answer

Scott Davies picture Scott Davies · Jul 9, 2009

The steps that I use for initial design (getting to a class diagram), are:

  1. Requirements gathering. Talk to the client and factor out the use cases to define what functionality the software should have.

  2. Compose a narrative of the individual use cases.

  3. Go through the narrative and highlight nouns (person, place, thing), as candidate classes and verbs (actions), as methods / behaviors.

  4. Discard duplicate nouns and factor out common functionality.

  5. Create a class diagram. If you're a Java developer, NetBeans 6.7 from Sun has a UML module that allows for diagramming as well as round-trip engineering and it's FREE. Eclipse (an open source Java IDE), also has a modeling framework, but I have no experience with it. You may also want to try out ArgoUML, an open source tool.

  6. Apply OOD principles to organize your classes (factor out common functionality, build hierarchies, etc.)

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