编码=设计？Yes!

If you're doing top-down design, you produce a specification that stops at some level of granularity. And you always risk discovering, come implementation time, that the module or class that was the lowest level of your specification hides untold worlds of complexity that will take as much development effort as you'd budgeted for the rest of the project combined. The only way to avoid that is to have your design go all the way down to specifying individual lines of code, in which case you aren't designing at all, you're just programming. 

如果你采用自顶向下的设计方式，那么你所实现的设计书在细节上必然会停留在某一层次。这样你就会时刻冒着如下的风险：当这些设计需要被实现的时候，你会发现曾经处于设计书最底层的模块或类中竟然隐藏着难以预想的复杂度，以至于实现它们开发者所需付出的努力竟然会花光该项目所有剩余的预算。要预防这种风险只有一种途径，那就是将设计进行到底使之到达并描述每一行代码。但如此这般你便根本不是在设计，你就是在编码。