Definition: Reusable solutions to commonly occurring problems in software design, originally documented by the Gang of Four across creational, structural, and behavioral categories.
— Source: NERVICO, Product Development Consultancy
What are Design Patterns
Design patterns are proven, reusable solutions to problems that appear repeatedly in software development. They are not code to copy directly, but conceptual templates adapted to each project’s specific context. They were formalized in 1994 by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, known as the Gang of Four (GoF).
They are classified into three categories: creational (how objects are created), structural (how they are composed), and behavioral (how they interact).
How they work
Each pattern describes a recurring problem, the general solution, and the consequences of applying it. Creational patterns like Factory or Singleton control how objects are instantiated. Structural patterns like Adapter or Facade organize composition between classes. Behavioral patterns like Observer or Strategy define how objects communicate and distribute responsibilities.
A developer identifies the problem at hand, maps it to a known pattern, and adapts the solution to the particular case. The goal is not to apply patterns for their own sake, but to recognize when a problem already has a well-studied solution.
Why they matter
Patterns provide a shared vocabulary among developers. When someone says “we use an Observer here,” the entire team understands the structure without lengthy explanations. They also reduce design errors because the solutions have been tested across thousands of real projects.
Practical example
A notification system needs to alert multiple services when an order changes status. Instead of coupling the order service to each recipient, the Observer pattern is applied. The order publishes a “status changed” event and each interested service (email, SMS, dashboard) subscribes independently. Adding a new notification channel does not require modifying the order service.