Series: Design Patterns and Analysis | Part 1 of 4 > Developed during Master’s in Web Systems Projects
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.
Series Navigation
- Introduction: Analysis Patterns
- Current: Part 1 - Design Patterns Overview
- Next: Part 2 - Creational Patterns
- Complete series: Analysis Patterns | Creational Patterns | Structural Patterns | Behavioral Patterns