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What are Design Patterns
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What are Design Patterns

پست شماره 18
  • تاریخ ارسال : دوشنبه 16 آبان 1390
  • بازدید : 515 مشاهده

 What are Design Patterns?

 

Sitting at your desk in front of your workstation, you stare into space,

trying to figure out how to write a new program feature. You know

intuitively what must be done, what data and what objects come into play,

but you have this underlying feeling that there is a more elegant and

general way to write this program.

In fact, you probably don’t write any code until you can build a picture in

your mind of what the code does and how the pieces of the code interact.

The more that you can picture this “organic whole,” or gestalt, the more

likely you are to feel comfortable that you have developed the best

solution to the problem. If you don’t grasp this whole right away, you may

keep staring out the window for a time, even though the basic solution to

the problem is quite obvious.

In one sense you feel that the more elegant solution will be more reusable

and more maintainable, but even if you are the sole likely programmer,

you feel reassured once you have designed a solution that is relatively

elegant and that doesn’t expose too many internal inelegancies.

One of the main reasons that computer science researchers began to

recognize design patterns is to satisfy this need for elegant, but simple,

reusable solutions. The term “design patterns” sounds a bit formal to the

uninitiated and can be somewhat offputting when you first encounter it.

But, in fact, design patterns are just convenient ways of reusing objectoriented

code between projects and between programmers. The idea

behind design patterns is simple—write down and catalog common

interactions between objects that programmers have frequently found

useful.

One of the frequently cited patterns from early literature on programming

frameworks is the Model-View-Controller framework for Smalltalk

(Krasner and Pope 1988), which divided the user interface problem into

three parts, as shown in Figure 1-1. The parts were referred to as a data

 

model, which contains the computational parts of the program; the view,

ontroller, which interacted

between the user and the view.

Design Patterns—Elements of Reusable Software, by Gamma,

Helm, Johnson, and Vlissides (1995). This book, commonly referred to as

the Gang of Four, or “GoF,” book, has had a powerful impact on those

seeking to understand how to use design patterns and has become an allCopyright

Design Patterns throughout this

book.

Since the publication of the original Design Patterns text, there have been

a number of other useful books published. One closely related book is The

Design Patterns Smalltalk Companion (Alpert, Brown, and Woolf 1998),

which covers the same 23 patterns from the Smalltalk point of view. We’ll

refer to this book throughout as the Smalltalk Companion. Finally, we

recently published Java Design Patterns: a Tutorial, and Visual Basic

Design Patterns, which illustrate all of these patterns in those languages.