文档介绍：Chapter 3
Design Principles and Patterns
Experienced designers evidently know something inexperienced others don’t.
What is it?
—Erich Gamma
In Chapter 1, “Architects and Architecture Today,” we focused on the true meaning of architecture
and the steps through which architects get a set of specifi cations for the development team.
We focused more on the process than the principles and patterns of actual design. In Chapter 2,
“UML Essentials,” we fi lled a gap by serving up a refresher (or a primer, depending on the reader’s
skills) of Unifi ed Modeling Language (UML). UML is the most popular modeling language through
which design is expressed municated within development teams.
When examining the bundle of requirements, the architect at fi rst gets a relatively blurred
picture of the system. As the team progresses through iterations, the contours of the picture
sharpen. In the end, the interior of the system unveils a web of interrelated classes applying
design patterns and fulfi lling design principles.
Designing a software system is challenging because it requires you to focus on today’s
requested features while ensuring that the resulting system be fl exible enough to support
changes and addition of new features in the future.
Especially in the past two decades, a lot has been done in the Information Technology (IT)
industry to make a systematic approach to software development possible. Methodologies,
design principles, and fi nally patterns have been developed to help guide architects to
envision and build systems of plexity in a disciplined way.
This chapter aims to provide you with a quick tutorial about software engineering. It fi rst outlines
some basic principles that should always inspire the design of a modern software system.
The chapter then moves on to discuss principles of object-oriented design. Along the way,
we introduce patterns, idioms, and aspect-orientation, as well as pearls o