What Are Design Patterns and Why Do We Need Them?

Software professionals may be familiar with the term "Design Patterns," but many have no idea of where they come from and what they truly are. Consequently, some do not see the value and benefits design patterns bring to the software development process, especially in the areas of maintenance and code reuse. This article will bridge this gap by defining design patterns from a historical perspective. It will also summarize the salient features of a typical design pattern and arrive at a working definition so that you will know what they are and what to expect when you incorporate them into your designs

What is Design Patterns

Design patterns are commonly defined as time-tested solutions to recurring design problems. The term refers to both the description of a solution that you can read, and an instance of that solution as used to solve a particular problem.

History 

Design patterns have their roots in the work of Christopher Alexander, a civil engineer who wrote about his experience in solving design issues as they related to buildings and towns. It occurred to Alexander that certain design constructs, when used time and time again, lead to the desired effect. He documented and published the wisdom and experience he gained so that others could benefit. 

After that software professionals began to incorporate Alexander's principles into the creation of early design pattern documentation as a guide to novice developers. This early work led others to also write about design patterns and culminated in the publication of Design Patterns: Elements of Reusable Object-Oriented Software in 1995 by Eric Gamma, Richard Helm, Ralph Johnson, and John Vlissides. This book is considered to be the "coming out" of design patterns to the software community at large and has been influential in the evolution of design patterns since. Design Patterns described 23 patterns that were based on the experience of the authors at that time.