Sometimes a design pattern can be a bit nerve-wracking when looking at implementation, but when designing a system, making mention of the pattern can help give a developer a more purposeful understanding of how an object or system is meant to be used.

For instance, a decorator pattern is useful when taking a base model and wrapping it with functionality or features. Most commonly you could see a Decorator pattern on websites that let you set features on a car or a computer. In those cases, a base model of a car or computer is selected, then you can add packages. A car may allow for a towing package, or an LED light bar, or something like that. A computer may allow for more memory, a better hard drive, or different processor, all selectable in their designer. Refactoring.guru has a more comprehensive description for each major design pattern that we see in the industry.

Below, you’ll find some common use cases for different design patterns:

Creational Patterns

1. Abstract Factory
   • Use Case: Creating families of related or dependent objects without specifying their concrete classes. For example, a GUI toolkit that can create buttons, checkboxes, and scrollbars for different operating systems (Windows, macOS, Linux).
2. Builder
   • Use Case: Constructing complex objects step by step. Useful for creating a complex Car object where the client can specify parts like engine type, GPS system, and seats.
3. Factory Method
   • Use Case: Defining an interface for creating an object, but letting subclasses alter the type of objects that will be created. For example, a document editor that can create different types of documents (Word, PDF).
4. Prototype
   • Use Case: Creating new objects by copying existing ones (cloning). For instance, a game that needs to spawn many similar enemies quickly.
5. Singleton
   • Use Case: Ensuring a class has only one instance and providing a global point of access to it. Useful for managing a shared resource like a database connection or a configuration object.

Structural Patterns

1. Adapter
   • Use Case: Allowing incompatible interfaces to work together. For example, a payment processing system that integrates multiple payment gateways with different APIs.
2. Bridge
   • Use Case: Decoupling an abstraction from its implementation so that the two can vary independently. For instance, separating the platform-specific window rendering logic from the window management logic in a GUI library.
3. Composite
   • Use Case: Composing objects into tree structures to represent part-whole hierarchies. For example, a graphics drawing application where shapes can be simple (like a line) or complex (like a group of shapes).
4. Decorator
   • Use Case: Adding behavior to objects dynamically without affecting other objects from the same class. For instance, adding scrolling and border features to a text view object in a GUI application.
5. Facade
   • Use Case: Providing a simplified interface to a complex subsystem. For example, a library system that provides a simple interface for checking out books while hiding complex logic involving user accounts, book inventory, and fines.
6. Flyweight
   • Use Case: Minimizing memory usage by sharing as much data as possible with similar objects. Useful in a text editor where each character is a flyweight object shared across multiple text documents.
7. Proxy
   • Use Case: Providing a surrogate or placeholder for another object to control access to it. For instance, a virtual proxy that loads a large image only when it’s needed.