Finished All 23 Patterns? Let’s Wrap It Up Together
This article marks the final installment in our 23-part series on classic object-oriented design patterns. Congratulations on making it to the end! Over the course of this series, we’ve explored each of the 23 Gang of Four design patterns in depth. In this wrap-up, we’ll summarize all 23 patterns at a high level, group them into their three classic categories, and reflect on how they map to real-world software design problems. All the individual pattern articles are available on the author’s blog (see the blog archive for links to each pattern), so consider this final piece as both a recap and a handy reference.
What are design patterns? In software engineering, design patterns are general, repeatable solutions to common problems in software design. Rather than reinventing the wheel each time a familiar design challenge arises, developers can turn to these proven blueprints. Patterns don’t give you ready-made code; instead, they provide templates on how to solve problems in a way that’s been shown to work. By following established patterns, you can improve code clarity and flexibility while tapping into a shared vocabulary with other developers. The 23 classic object-oriented patterns we covered were originally popularized in the 1994 Design Patterns book by the “Gang of Four” (Gamma, Helm, Johnson, Vlissides) — and they remain essential knowledge for modern engineers.
Below, we’ll briefly revisit the three categories of design patterns — Creational, Structural, and Behavioral — with an accessible introduction to each. We won’t dive into the nitty-gritty of each pattern here (no worries, we won’t repeat all the detailed descriptions you saw in earlier parts!), but we will highlight what each category is about and list the patterns it includes. We’ll finish with a convenient “pattern field guide” — a summary table that you can bookmark as a quick reference for all 23 patterns, their use cases, and their pros and cons. Let’s get started.
Creational Design Patterns — Flexible Object Creation
Creational patterns focus on the process of object creation. Instead of instantiating objects directly in your code with new, creational patterns provide flexible mechanisms for making new objects, enhancing your program’s extensibility and reducing tight coupling. These patterns are especially handy when object creation is complex, multi-step, or tightly coupled to specific classes – situations where you want to abstract away the specifics of how objects are constructed. By using creational patterns, you gain more control over what gets created and when, which leads to code that’s easier to adapt as requirements evolve.
In this series, we covered five creational patterns: Singleton, Factory Method, Abstract Factory, Builder, and Prototype. Each of these tackles object creation from a different angle. For example, some ensure that only a single instance of a class exists globally (Singleton), while others separate the construction of complex objects from their representation (Builder) or let you choose which class to instantiate at runtime (Factory Method). What they all share is an emphasis on making the instantiation process more flexible and powerful than the basic class constructor. Creational patterns help you avoid hard-coding specific classes in your code, making it easier to change how objects are created — say, to switch databases or UI themes — without touching the high-level code that uses those objects.
We’ve seen how Creational patterns give us flexibility in creating objects. Next, let’s turn to Structural patterns, which address how classes and objects are organized and combined in larger systems.
Structural Design Patterns — Organizing Object Relationships
Structural design patterns deal with how objects and classes fit together to form larger structures. They help you ensure that when you combine components, the result is flexible and efficient in terms of structure. In essence, structural patterns are about building relationships — for example, adapting interfaces so that otherwise incompatible classes can work together, or composing objects into tree hierarchies to represent part-whole relationships. By using structural patterns, you can create architectures that are easier to maintain and extend, since the relationships between pieces are well-defined and decoupled.
We discussed seven structural patterns in this series: Adapter, Bridge, Composite, Decorator, Facade, Flyweight, and Proxy. Each pattern in this category helps structure your code in a particular way. Some patterns act as connectors — for instance, Adapter wraps one interface to make it compatible with another, allowing you to integrate legacy components or external libraries without modifying their code. Others, like Composite, let you treat groups of objects and individual objects uniformly (think of a file system where folders and files are both “nodes” that you can operate on similarly). There are patterns that add functionality dynamically — for example, Decorator lets you attach new behaviors to objects at runtime by wrapping them, which is more flexible than subclassing. And there are those that introduce simplifying intermediaries — a Facade provides a unified, easy-to-use interface to a complex subsystem, while a Proxy acts as a stand-in for another object to control access to it (whether for lazy loading, security, or remote communication). By applying structural patterns, you make the overall design more modular and understandable, since each pattern addresses a clear problem in object relationships (be it interface mismatch, redundant data, or complex internals) with a proven solution.
Having covered how we create objects and organize them, the final piece of the puzzle is how objects behave and interact. That’s where the third category — Behavioral patterns — comes in.
Behavioral Design Patterns — Managing Object Interactions and Responsibilities
Behavioral design patterns are all about communication between objects: how objects cooperate, how responsibilities are distributed among them, and how to manage complex flows of control in a clean way. Rather than focusing on creation or structural composition, behavioral patterns define how algorithms work and how objects communicate at runtime. They help you write code where interactions are flexible and loosely coupled, making it easier to add new behaviors or modify the interaction patterns between components without breaking everything. In scenarios like orchestrating a workflow, implementing undo/redo, or broadcasting events to multiple subscribers, behavioral patterns provide time-tested approaches.
This series covered eleven behavioral patterns: Chain of Responsibility, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, and Visitor. Each of these patterns addresses a common interaction scenario or allocation of responsibility. For example, Observer defines a publish/subscribe mechanism so that when one object’s state changes, all dependent objects get notified automatically — think of UI components updating when the underlying data changes. Strategy encapsulates interchangeable algorithms so you can swap them in and out (say, different sorting methods) without changing the code that uses them. Some patterns introduce an intermediary to simplify communication: Mediator centralizes complex communication among multiple objects, so those objects don’t have to refer to each other directly. Others help with controlling the flow of a process: Chain of Responsibility passes a request along a chain of handlers until one handles it (useful for things like event handling or approval pipelines), and Command turns a request into a stand-alone object — enabling features like queuing, logging, or undoable operations. We also saw patterns that manage state and behavior: State lets an object change its behavior when its internal state changes (avoiding lots of if/else logic), and Template Method defines the skeleton of an algorithm in a base class, allowing subclasses to fill in the details. By using behavioral patterns, you can make complex workflows easier to understand and extend. They tend to reduce tight coupling by separating “what gets done, when and by whom” into distinct layers, so that changing one part of the interaction (like adding a new command or a new state) doesn’t ripple unpredictably through the codebase.
Conclusion
You’ve completed the journey through all 23 classic design patterns! By now, you’ve not only learned the individual patterns but also when and why to apply them. This final overview is a testament to how far you’ve come: from understanding simple creational tricks like Singleton to mastering complex behavioral workflows with patterns like Observer or Visitor. Feel free to save this article to your reading list as a future reference. You might find yourself coming back to the summary table or the problem-pattern mapping when you’re architecting your next application. And if you found this series helpful, consider giving it a clap or sharing it with your fellow developers so they can benefit too.
I’d love to hear your thoughts — please leave a comment with your experiences or questions about these patterns. Also, don’t forget to follow my blog for more developer content. Although this design patterns series has concluded, I regularly write about other software development topics as well. You can check out my other series on Dart/Flutter, Clean Architecture, and even posts on Leadership and Effective Team Management. Who knows — the knowledge you gained here might be the bridge to those advanced topics, or vice versa!
Thank you for reading and happy coding! Remember: design patterns are powerful tools in your toolkit, but the real art is knowing when to use each one. With practice and experience, you’ll naturally recognize scenarios in your projects where a pattern fits perfectly. Until next time, happy architecting — and keep building clean, maintainable, and elegant software solutions. 🎉
