COMMON DESIGN PATTERNS

The Design Patterns book by Gamma et al. (often referred to as “The Gang of Four”), takes a formal and detailed approach to describing 23 fundamental design patterns. It groups these patterns into three basic categories: creational, behavioral, and structural. In the following pages we’ll look at a variety of patterns from these categories to understand what patterns are and how they’re used.

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NOTE

Other design pattern categories have been developed, including concurrency patterns useful in concurrent programming. These patterns tend to be domain-specific and are not as widely known as the patterns in the three core categories.

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Singleton

The Singleton pattern ensures that at most one instance of a class exists at any given time. This instance acts as a gatekeeper to shared resources or as a central communications hub. An application cannot create new instances—all methods are accessed through the singleton. The application...