Design patterns are common solutions to recurring problems in software design. They represent best practices refined over time and provide a standard way to organize and structure code, making it more modular, maintainable, and reusable.
The three main categories of design patterns along with some commonly used patterns in each:
- Creational Design Patterns
- Structural Design Patterns
- Behavioral Design Patterns
While there are many design patterns available, a few stand out as the most commonly used and important across software development because of their widespread applicability and utility. Below are some of the most important design patterns that every developer should be familiar with:
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Singleton Pattern (Creational)
• Purpose: Ensures that a class has only one instance and provides a global point of access to it.
• Where it’s used: Database connections, configuration managers, logging systems.
• Importance: It controls access to a single instance of a class, especially in resource-heavy applications.
Example Use Case: A database connection pool where only one instance of the connection pool is maintained.
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• Purpose: Provides an interface for creating objects but allows subclasses to decide which class to instantiate.
• Where it’s used: In scenarios where object creation is complex and requires conditional logic.
• Importance: It abstracts the process of object creation, making your code more flexible and easier to extend.
Example Use Case: A vehicle factory that produces Car, Truck, or Bike based on input.
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• Purpose: Defines a one-to-many relationship where changes to one object notify multiple dependent objects.
• Where it’s used: Event handling systems, notification systems, MVC frameworks.
• Importance: It decouples the subject (the object being observed) from the observers, allowing for modular code where components can react to changes in other components.
Example Use Case: A news website where subscribers (observers) are notified when a new article (subject) is published.
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• Purpose: Defines a family of algorithms, encapsulates each one, and makes them interchangeable.
• Where it’s used: In situations where multiple algorithms can be chosen dynamically at runtime.
• Importance: It allows for different algorithms or strategies to be selected based on the context without modifying the client code.
Example Use Case: Different payment methods (credit card, PayPal, cryptocurrency) in an e-commerce system.
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Decorator Pattern (Structural)
• Purpose: Adds responsibilities to objects dynamically without modifying their structure.
• Where it’s used: When you need to extend the behavior of objects in a flexible way, like adding features to GUI components.
• Importance: It provides a more flexible alternative to subclassing for extending functionality.
• Decorator class is the abstract class which is excented by sub decorator classes
Example Use Case: A text editor where different decorators (bold, italic, underline) can be applied to a text object.
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• Purpose: Converts the interface of a class into another interface that clients expect.
• Where it’s used: Integrating legacy code, when systems with incompatible interfaces need to work together.
• Importance: It helps in reusing existing code without changing it, by adapting it to work with new systems or interfaces.
Example Use Case: Adapting a third-party library that uses a different interface to fit into your system’s architecture.
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• Purpose: Encapsulates a request as an object, thereby allowing clients to queue, log, and undo operations.
• Where it’s used: Undo/redo functionality, transaction systems.
• Importance: It decouples the sender of a request from its receiver, allowing for more flexible architectures where commands can be queued, logged, or undone.
Example Use Case: A remote control where each button press is treated as a command object that can be executed, reversed, or logged.
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• Purpose: Provides a unified interface to a set of interfaces in a subsystem, simplifying the complexity of the system.
• Where it’s used: When dealing with complex systems, libraries, or APIs where a simpler interface is desirable.
• Importance: It reduces the complexity for clients and makes a system easier to use.
Example Use Case: A simplified API for complex interactions with a third-party payment gateway.
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• The Builder Pattern is a creational design pattern that allows you to create complex objects step by step. Unlike other creational patterns, the Builder pattern separates the construction of a complex object from its representation, allowing you to create different representations by reusing the same construction process.
• It is usefull when :-
- The object you want to create has multiple fields, especially optional fields.
- You want to create an object in a step-by-step process while keeping the construction logic separate from the object’s representation.
Example Use Case: Creating a complex meal order where you can choose specific ingredients, drink, and dessert.
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Prototype Pattern (Creational)
• Purpose: Creates new objects by cloning an existing object, useful when object creation is expensive.
• Where it’s used: In scenarios where creating a new instance of a class is costly (e.g., resource-heavy or time-consuming).
• Importance: It reduces the cost of creating new objects by copying an existing instance.
Example Use Case: Copying an object in a game like a character or a weapon with its current state.
Why These Patterns are Important
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Reusability: These patterns are designed to solve common problems in a reusable manner.
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Maintainability: They promote clean, modular, and maintainable code structures.
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Scalability: Design patterns help in building software that can scale and evolve without needing major refactoring.
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Decoupling: Many patterns, like the Observer, Command, and Facade, help decouple code, reducing dependencies and increasing flexibility.
When to Use Design Patterns
• Complexity Management: Use patterns when your codebase grows complex, and you need modular, reusable, and scalable solutions. • Common Solutions: When faced with a recurring problem or design challenge, patterns provide tried-and-tested solutions. • Team Collaboration: Patterns provide a common language for developers, helping teams collaborate more effectively.
These are some of the most important design patterns that every developer should understand. They provide powerful solutions to common architectural challenges and help you write more efficient, maintainable, and scalable software.