When to use a design pattern?

You should use a design pattern when you encounter a recurring problem in software design that has a well-established, proven solution. Design patterns provide best practices for addressing these common issues, leading to code that is more flexible, maintainable, and scalable. Here’s a guide on when to use design patterns and how they help streamline the development process:

1. To Solve Recurrent Design Problems

• When: If you find that a specific problem arises frequently (e.g., object creation, communication between objects, or adding functionality to existing classes), a design pattern can offer a standardized solution.
• Example: If you frequently need a single instance of a class, use the Singleton Pattern to manage this requirement efficiently.

2. When Flexibility and Scalability Are Required

• When: If you know your system needs to evolve with minimal changes, design patterns can help create a flexible foundation.
• Example: The Factory Pattern allows you to create different types of objects at runtime, making it easier to extend your system without changing the core logic.

3. To Enhance Code Readability and Maintainability

• When: If your code becomes difficult to understand or modify, a design pattern can simplify structure, making it easier for other developers to read and maintain.
• Example: The Facade Pattern can reduce complexity by providing a simplified interface to a complex subsystem, making it easier for team members to work with.

4. To Avoid Repeating Code

• When: If you notice code duplication or repeated logic, a design pattern can encapsulate this logic in a reusable way, promoting DRY (Don't Repeat Yourself) principles.
• Example: The Decorator Pattern allows you to add new functionality to objects without modifying their structure, avoiding duplicated functionality across classes.

5. When Consistency and Standardization Are Required

• When: If you’re working in a team, design patterns can provide a shared language for common structures, helping team members understand and contribute to each other's code more easily.
• Example: By using the Observer Pattern for event handling, everyone on the team knows where to look when managing event-driven updates.

6. To Simplify Complex Object Interactions

• When: If multiple objects in your system need to communicate or collaborate in complex ways, design patterns can help structure these interactions effectively.
• Example: The Mediator Pattern centralizes communication between multiple objects, reducing dependencies and simplifying the relationships between components.

7. When You Need Dynamic Behavior or Configuration

• When: If you need to select or change the behavior of an object at runtime, a design pattern can help you do this flexibly.
• Example: The Strategy Pattern allows for interchangeable algorithms that can be selected at runtime, useful for scenarios like choosing different sorting or payment methods dynamically.

8. To Separate Concerns and Organize Code Better

• When: If you’re trying to isolate different responsibilities within a system, design patterns help by clearly defining roles and interactions.
• Example: The MVC Pattern (Model-View-Controller) separates the data layer, presentation layer, and user input handling, making it easy to update one part without affecting others.

9. To Ensure Efficient Resource Management

• When: If your system relies on resources that need to be managed carefully (e.g., database connections, network connections), a design pattern can ensure efficient management of these resources.
• Example: The Singleton Pattern is often used to manage shared resources, like a database connection pool, ensuring only one instance manages the resource.

10. When You Need Decoupled, Modular Code

• When: If you want to make parts of your system independent of each other to facilitate modularity, a design pattern can help achieve this.
• Example: The Adapter Pattern enables you to make incompatible classes work together without modifying their code, decoupling them from each other.

Common Scenarios and Recommended Patterns

• Creating Complex Objects: Use Builder Pattern to construct objects with many configuration options.
• Providing a Simplified Interface: Use Facade Pattern to expose only essential parts of a complex subsystem.
• Managing Dependencies Between Objects: Use Observer Pattern for dependency management where multiple objects need to be updated based on another object’s state.
• Configuring Object Behavior at Runtime: Use Strategy Pattern to select an algorithm or behavior dynamically.
• Structuring UI Elements: Use MVC (Model-View-Controller) or MVVM (Model-View-ViewModel) for user interfaces to separate logic and data.

Summary

Use a design pattern whenever you:

• Face a well-known design problem with a standard solution.
• Need to improve flexibility, readability, and maintainability.
• Are building systems that need modularity, scalability, or clear separation of concerns.
• Are working with complex object relationships, resource management, or reusable components.

Using design patterns helps you write cleaner, more maintainable code that’s easier to understand, extend, and debug, benefiting both you and your team in the long run.