Programming Interviews Exposed, 4th Edition

12Design Patterns

No two programming projects are the same, but the problems that need to be solved often recur across many otherwise dissimilar projects. Much of this book concerns data structures and algorithms: recipes for solving common and recurrent problems in computation and storage. Another class of common problems relates to how to organize and structure your code for maximum clarity, efficiency, reliability, and reusability. The solutions to these kinds of problems are called design patterns.

WHAT ARE DESIGN PATTERNS?

Design patterns are guidelines for identifying and solving common design problems in object-oriented programming. Unlike frameworks or class libraries, design patterns are abstract, providing recommendations on how to solve specific kinds of programming problems without providing fully fleshed-out code to implement those recommendations. They distill years of software programming experience into a set of organizational principles for object-oriented application architecture.

Design patterns were popularized and formalized in the 1990s by the publication of Design Patterns: Elements of Reusable Object Oriented Software,¹ but the ideas predate the book. Many of the core design patterns, like Iterator and Singleton, are widely used and familiar to most Java and C++ programmers. Other patterns, like Builder, are less frequently used but are highly useful in the appropriate situation.

Why Use Design Patterns?

Design patterns are useful for two reasons. ...