|
a6700a7
|
Keep Coupling Loose Coupling describes how tightly a class or routine is related to other classes or routines. The goal is to create classes and routines with small, direct, visible, and flexible relations to other classes and routines, which is known as "loose coupling." The concept of coupling applies equally to classes and routines, so for the rest of this discussion I'll use the word "module" to refer to both classes and routines. Good ..
|
|
|
Steve McConnell |
|
a7976b6
|
Keep Your Design Modular Modularity's goal is to make each routine or class like a "black box": You know what goes in, and you know what comes out, but you don't know what happens inside."
|
|
|
Steve McConnell |
|
10fd5b5
|
The concept of modularity is related to information hiding, encapsulation, and other design heuristics. But sometimes thinking about how to assemble a system from a set of black boxes provides insights that information hiding and encapsulation don't, so the concept is worth having in your back pocket.
|
|
|
Steve McConnell |
|
60bbd48
|
Summary of Design Heuristics Here's a summary of major design heuristics: More alarming, the same programmer is quite capable of doing the same task himself in two or three ways, sometimes unconsciously, but quite often simply for a change, or to provide elegant variation. -- A. R. Brown W. A. Sampson Find Real-World Objects Form Consistent Abstractions Encapsulate Implementation Details Inherit When Possible Hide Secrets (Information Hidin..
|
|
|
Steve McConnell |
|
0ccc9a4
|
One of the most effective guidelines is not to get stuck on a single approach. If diagramming the design in UML isn't working, write it in English. Write a short test program. Try a completely different approach. Think of a brute-force solution. Keep outlining and sketching with your pencil, and your brain will follow. If all else fails, walk away from the problem. Literally go for a walk, or think about something else before returning to t..
|
|
|
Steve McConnell |
|
ad40ac4
|
Make interfaces programmatic rather than semantic when possible. Each interface consists of a programmatic part and a semantic part. The programmatic part consists of the data types and other attributes of the interface that can be enforced by the compiler. The semantic part of the interface consists of the assumptions about how the interface will be used, which cannot be enforced by the compiler. The semantic interface includes considerati..
|
|
|
Steve McConnell |
|
3821fa3
|
If you can't figure out how to use a class based solely on its interface documentation, the right response is not to pull up the source code and look at the implementation. That's good initiative but bad judgment. The right response is to contact the author of the class and say "I can't figure out how to use this class."
|
|
|
Steve McConnell |
|
9e27d76
|
Design is sloppy because a good solution is often only subtly different from a poor one.
|
|
|
Steve McConnell |
|
da9bfe8
|
Design is also sloppy because it's hard to know when your design is "good enough." How much detail is enough? How much design should be done with a formal design notation, and how much should be left to be done at the keyboard? When are you done? Since design is open-ended, the most common answer to that question is "When you're out of time."
|
|
|
Steve McConnell |
|
14dac4e
|
Computing pioneer Edsger Dijkstra pointed out that computing is the only profession in which a single mind is obliged to span the distance from a bit to a few hundred megabytes, a ratio of 1 to 109, or nine orders of magnitude (Dijkstra 1989).
|
|
|
Steve McConnell |
|
470079a
|
the automatic computer confronts us with a radically new intellectual challenge that has no precedent in our history." Of course software has become even more complex since 1989, and Dijkstra's ratio of 1 to 109could easily be more like 1 to 1015 today."
|
|
|
Steve McConnell |
|
86e21f3
|
Dijkstra pointed out that no one's skull is really big enough to contain a modern computer program (Dijkstra 1972), which means that we as software developers shouldn't try to cram whole programs into our skulls at once; we should try to organize our programs in such a way that we can safely focus on one part of it at a time.
|
|
|
Steve McConnell |