After learning about analysis patterns to model business concepts, we now shift focus to the structural challenges of writing software. This is where design patterns shine — reusable architectural ideas that help us write cleaner, more maintainable code.
What Is a Design Pattern?
A design pattern is a typical, reusable solution to a common software design problem. Think of it as a template or blueprint: it doesn’t give you ready-made code, but a structured way of thinking about a recurring problem in your system.
Design patterns are not libraries or functions you can copy-paste. Instead, they describe abstract relationships between classes and objects that you can adapt to your use case.
A pattern is to code what a blueprint is to a building: it helps you structure the solution before pouring concrete.
Why Use Design Patterns?
Here’s what makes them essential:
- Communication: They give teams a shared vocabulary. Saying “this is a decorator” immediately tells other developers what to expect.
- Maintainability: Patterns encourage loose coupling and solid principles, making code easier to evolve.
- Reusability: Abstracting repeated structure avoids reinventing solutions.
What Makes Up a Pattern?
Most documented patterns include:
- Intent: What the pattern solves (problem + high-level idea).
- Motivation: When and why it’s useful.
- Structure: UML diagrams and class interactions.
- Code Examples: Often shown in Java, C++, Python or TypeScript.
- Consequences: Trade-offs (e.g., memory use vs. flexibility).
The Catalog of Design Patterns
The classic “Gang of Four” book classifies 23 design patterns into three categories: [“Architecture”]
Creational Patterns
How to create objects in a flexible, reusable way.
- Factory Method
- Abstract Factory
- Builder
- Prototype
- Singleton
Use when: you want to separate object construction from its representation or ensure controlled instantiation.
Structural Patterns
How to compose objects into larger structures.
- Adapter
- Bridge
- Composite
- Decorator
- Facade
- Flyweight
- Proxy
Use when: you want to decouple implementation from interface or add behavior without inheritance.
Behavioral Patterns
How to manage communication and responsibilities between objects.
- Chain of Responsibility
- Command
- Iterator
- Mediator
- Memento
- Observer
- State
- Strategy
- Template Method
- Visitor
Use when: you want to encapsulate algorithms, manage event propagation, or switch behavior dynamically.
Pattern vs Algorithm
An algorithm is a fixed sequence of steps to solve a task (e.g., quicksort). A pattern is a reusable structure that lets you decide how to build those steps in your software. You can implement a pattern in many ways.
Cooking analogy: An algorithm is a recipe. A pattern is the idea of “baking” or “marinating.”
Conclusion
Design patterns are time-tested thinking tools. They help us go beyond just writing code — we design systems.
In upcoming posts, we’ll go deeper into each category with concrete UML diagrams, when to use them, and examples that highlight trade-offs and variations.
Stay tuned for real-world applications of Factory, Strategy, Observer, and more.