关于软件设计各种思想的体系—目标/特性/方法/原则和模式

比喻的不错。

是不是也可以这样理解，软件的终极目标，就是复用。
可复用的软件一定是可扩展的，可扩展的一定具有高内聚、底偶合的特点。

而软件设计原则是达到这个目标的通道。设计模式是这个终极目标的表现方式。

那么可重用行跟可维护性之间有什么关系呢？是不是复用度高的的软件可维护性就高呢？
复用度高的程序--->内聚性强--->可维护性高
复用性高的程序其内聚性一定强，内聚性强的程序则更容易维护

13.1 A Reality Check            by William Opdyke
I worked at Bell Labs for several years before I decided to pursue my doctoral studies. Most of
that time was spent working in a part of the company that developed electronic switching
systems. Such products have very tight constraints with respect to both reliability and the speed
with which they handle phone calls. Thousands of staff-years have been invested in developing
and evolving such systems. Product lifetimes have spanned decades. Most of the cost of
developing these systems comes not in developing the initial release but in changing and
adapting the systems over time. Ways to make such changes easier and less costly would result
in a big win for the company.

I can vividly recall presenting a talk in early 1993 at a technology exchange forum for staff at
AT&T Bell Labs and NCR (we were all part of the same company at the time). I was given 45
minutes to speak on refactoring. At first the talk seemed to go well. My enthusiasm for the topic
came across. But at the end of the talk, there were very few questions. One of the attendees
came up afterward to learn more; he was beginning his graduate work and was fishing around for
a research topic. I had hoped to see some members of development projects show eagerness in
applying refactoring to their jobs. If they were eager, they didn't express it at the time.
People just didn't seem to get it.

Over the next couple years, I had numerous opportunities to talk about refactoring at AT&T Bell
Labs internal forums and at outside conferences and workshops. As I talked more with
developers in the trenches, I started to understand why my earlier messages didn't come across
clearly. The disconnect was caused partly by the newness of object-oriented technology. Those
who had worked with it had rarely progressed beyond the initial release and hence had not yet
faced the tough evolution problems refactoring can help solve. This was the typical researcher's
dilemma—the state of the art was beyond the state of common practice. However, there was
another, troubling cause for the disconnect. There were several commonsense reasons
developers, even if they bought into the benefits of refactoring, were reluctant to refactor their
programs. These concerns had to be addressed before refactoring could be embraced by the
development community.

随着与一线开发人员的交谈越来越多，我开始明白为什么以前的演讲不能感染别人。我与听众的距离有一部分是因为面向对象技术自身就很新。那些使用它的人多半都还没有完成第一个版本的开发，所以还没有遇到[演进]这个大的问题，而这个问题是重构能够帮忙解决的。

EJB 不是组件级别的重用吗？

可维护性就是重用性，软件的第一个维护者是开发者本人。
可维护性依靠扩展性，扩展性来自对变化的适应力，而不是对变化的预先判断。
开发迅速，节约成本，高效灵活，结构清晰……这些好的特征在软件上经常是同时存在，同时消失。

可维护性就是重用性，软件的第一个维护者是开发者本人。
可维护性依靠扩展性，扩展性来自对变化的适应力，而不是对变化的预先判断。
开发迅速，节约成本，高效灵活，结构清晰……这些好的特征在软件上经常是同时存在，同时消失。