Design Patterns

Design patterns are solutions for common architectural problems in software engineering. They serve as a technology-independent blueprint to solve recurring problems on a conceptual level.

Although not tied to a specific programming language, most patterns rely heavily on OOP concepts, especially those defined by the Gang of Four. Due to their object-oriented nature, UML is a very convenient way to describe their structure.

The following catalogue contains a selection of some commonly used patterns, each illustrated by a UML class diagram, followed by a more detailed textural description. The drawings are free to use for your own blog, lecture or whatever project you want to use them for.

More patterns will follow, so stay tuned for further updates!

If you like, please share your thoughts about these patterns on Twitter (@UMLBoard) or just send me a message.

api gateway

Do you have many microservices performing different tasks together but you still want easy access to the overall system? Then an API Gateway could be the solution.
bridge

You have many base classes with different features, but combining them would result in a large class hierarchy? The Bridge pattern can reduce the number of classes in your design.
command

You're looking for a way to undo/redo user actions, or you need some kind of transaction handling? The Command pattern is here to help.
factory method

The Factory Method lets you separate the logic for creating an object from the place where it's actually instantiated. A powerful tool for reducing dependencies in your code base.
null object

The Null Object pattern allows you to create a placeholder for objects that don't exist.
observer

Have you changed one object and want other objects to be notified about this change? Use the Observer pattern to propagate updates between objects while keeping them loosely coupled.
publisher-subscriber

Experiencing issues with tight coupling in your application's components? The Publisher-Subscriber pattern can assist in decoupling communication between them.
repository

Your database layer is constantly leaking into your business code? The repository pattern can help to keep your implementations separated.
visitor

You want to add new functionality to an existing object structure but don't want to (or can't) change the objects' implementation? Then the Visitor pattern might be a good match!