Promise of OO OO has been hyped to the extent you'd figure it would solve world hunger and usher in a new era of world peace. Not! OO is an approach, a philosophy, it's not a recipe which blindly followed yields quality.
Robert Martin put OO in perspective: OO, when properly employed, does enhance the reusability of software. But it does so at the cost of complexity and design time. Reusable code is more complex and takes longer to design and implement. Furthermore, it often takes two or more tries to create something that is even marginally reusable. OO, when properly employed, does enhance the software's resilience to change. But it does so at the cost of complexity and design time. This trade off is almost always a win, but it is hard to swallow sometimes. OO does not necessarily make anything easier to understand. There is no magical mapping between the software concepts and every human's map of the real world. Every person is different. What one person percieves to be a simple and elegant design, another will perceive as convoluted and opaque. If a team has been able, by applying point 1 above, to create a repository of reusable items, then development times can begin to shrink significantly due to reuse. If a team has been able, by applying point 2 above, to create software that is resilient to change, then maintenance of that software will be much simpler and much less error prone.
Thin vs. Fat Class Interfaces How many methods should an object have? The right answer of course is just the right amount, we'll call this the Goldilocks level. But what is the Goldilocks level? It doesn't exist. You need to make the right judgment for your situation, which is really what programmers are for :-)
The two extremes are thin classes versus thick classes. Thin classes are minimalist classes. Thin classes have as few methods as possible. The expectation is users will derive their own class from the thin class adding any needed methods.
While thin classes may seem "clean" they really aren't. You can't do much with a thin class. Its main purpose is setting up a type. Since thin classes have so little functionality many programmers in a project will create derived classes with everyone adding basically the same methods. This leads to code duplication and maintenance problems which is part of the reason we use objects in the first place. The obvious solution is to push methods up to the base class. Push enough methods up to the base class and you get thick classes.
Thick classes have a lot of methods. If you can think of it a thick class will have it. Why is this a problem? It may not be. If the methods are directly related to the class then there's no real problem with the class containing them. The problem is people get lazy and start adding methods to a class that are related to the class in some willow wispy way, but would be better factored out into another class. Judgment comes into play again.
Thick classes have other problems. As classes get larger they may become harder to understand. They also become harder to debug as interactions become less predictable. And when a method is changed that you don't use or care about your code will still have to be retested, and rereleased.
Recent Changes 2000-11-16. Release
© Copyright 1995-2000. Todd Hoff and Fredrik Kristiansen. All rights reserved.
您可能感兴趣的文章: