Types of design pattern in web app development

 

Design Patterns and Their Usage

Design patterns are well-proven solutions to recurring software design problems. They provide a structured approach to solving common coding challenges and improve code reusability, scalability, and maintainability. Design patterns are broadly classified into three categories:

1. Creational Design Patterns

Creational patterns deal with object creation mechanisms, trying to create objects in a manner suitable for the situation.

1. Singleton

• Use Case: Ensures that only one instance of a class exists and provides a global point of access.
• Example: Logger, Database connections.

2. Factory

• Use Case: Creates objects without specifying the exact class.
• Example: ShapeFactory to create different shape objects.

3. Abstract Factory

• Use Case: Creates a family of related objects without specifying concrete classes.
• Example: GUI toolkits that support multiple platforms.

4. Builder

• Use Case: Separates object construction from its representation.
• Example: Creating complex objects like a multi-step construction of a car or a meal.

5. Prototype

• Use Case: Creates new objects by copying an existing object.
• Example: Cloning an object with modifications.

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2. Structural Design Patterns

Structural patterns focus on organizing classes and objects to form larger structures efficiently.

6. Adapter

• Use Case: Allows incompatible interfaces to work together.
• Example: Converting XML data to JSON format.

7. Composite

• Use Case: Treats individual objects and compositions of objects uniformly.
• Example: File system (files and directories treated uniformly).

8. Proxy

• Use Case: Acts as a placeholder to control access to another object.
• Example: Virtual proxy for image loading, security proxy.

9. Flyweight

• Use Case: Reduces memory usage by sharing common parts of objects.
• Example: Large-scale text processing where similar characters share memory.

10. Facade

• Use Case: Provides a simplified interface to a complex subsystem.
• Example: Simplified API for a complex library.

11. Bridge

• Use Case: Decouples abstraction from implementation, allowing both to vary independently.
• Example: Different device drivers in a GUI framework.

12. Decorator

• Use Case: Adds behavior dynamically to objects.
• Example: Adding scrolling functionality to a window.

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3. Behavioral Design Patterns

Behavioral patterns deal with communication between objects and responsibility distribution.

13. Template Method

• Use Case: Defines a skeleton of an algorithm, letting subclasses override certain steps.
• Example: Sorting algorithms.

14. Mediator

• Use Case: Reduces dependencies between communicating objects by centralizing communication.
• Example: Chatroom system where users communicate via a mediator.

15. Chain of Responsibility

• Use Case: Passes requests along a chain of handlers.
• Example: Logging system with multiple severity levels.

16. Observer

• Use Case: Defines a one-to-many dependency between objects.
• Example: Event listeners in UI.

17. Strategy

• Use Case: Defines a family of interchangeable algorithms.
• Example: Sorting algorithms (Bubble Sort, Quick Sort).

18. Command

• Use Case: Encapsulates a request as an object.
• Example: Undo/redo functionality.

19. State

• Use Case: Allows an object to alter behavior when its internal state changes.
• Example: Vending machine state transitions.

20. Visitor

• Use Case: Separates algorithms from the objects on which they operate.
• Example: Tax calculations for different product types.

21. Iterator

• Use Case: Provides a way to access elements of a collection sequentially without exposing details.
• Example: Iterating over a list in Python.

22. Interpreter

• Use Case: Defines a grammar and interprets expressions.
• Example: SQL query execution.

23. Memento

• Use Case: Captures and restores an object's internal state.
• Example: Save and restore game progress.

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These design patterns help developers structure their applications for better flexibility, maintainability, and scalability.

Here is a table differentiating the three categories of design patterns:

Category	Purpose	Example Patterns	Use Cases
Creational Patterns	Focuses on the creation of objects in a flexible and reusable manner.	Singleton, Factory, Abstract Factory, Builder, Prototype	Managing object creation, ensuring only one instance exists, creating families of objects, or cloning objects efficiently.
Structural Patterns	Helps in organizing and composing classes and objects to form larger structures efficiently.	Adapter, Composite, Proxy, Flyweight, Facade, Bridge, Decorator	Adapting incompatible interfaces, simplifying complex subsystems, sharing resources, or extending functionality dynamically.
Behavioral Patterns	Defines communication and interaction between objects while ensuring flexibility.	Template Method, Mediator, Chain of Responsibility, Observer, Strategy, Command, State, Visitor, Iterator, Interpreter, Memento	Managing event handling, ensuring loose coupling, defining algorithms, encapsulating commands, handling object state transitions.

This table provides a clear distinction between different types of design patterns along with their purposes and common use cases.

There is no single "best" design pattern because each pattern serves a different purpose. The choice of a design pattern depends on the specific problem you are trying to solve. Below is a comparison of when to use different types of design patterns based on different software needs.

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When to Use Different Design Patterns?

Scenario	Best Design Pattern	Why?
Need to ensure only one instance of a class exists	Singleton	Ensures a single instance and provides global access.
Want to create objects dynamically without specifying exact classes	Factory / Abstract Factory	Provides flexibility by encapsulating object creation logic.
Building a complex object step by step	Builder	Separates construction from representation, making it more readable.
Need to use existing class with an incompatible interface	Adapter	Converts one interface into another to ensure compatibility.
Want to treat a group of objects as a single entity	Composite	Allows hierarchical structures like file systems or UI components.
Need to add responsibilities dynamically to an object without modifying it	Decorator	Provides flexibility to add features at runtime.
Want to reduce object creation cost by sharing resources	Flyweight	Optimizes memory usage by reusing existing objects.
Simplifying interactions with a complex system	Facade	Provides a unified interface to a complex subsystem.
Need to centralize communication between objects	Mediator	Reduces dependencies between objects for better maintainability.
Need to define a one-to-many dependency where changes in one object affect others	Observer	Used in event-driven systems like UI listeners or stock market updates.
Want to allow multiple strategies for an algorithm at runtime	Strategy	Encapsulates different algorithms so they can be swapped easily.
Need a way to execute commands with undo/redo functionality	Command	Encapsulates operations as objects to enable undo/redo actions.
Want to pass requests through a chain of handlers	Chain of Responsibility	Allows multiple objects to process a request without knowing about each other.
Need to save and restore an object's state	Memento	Used in scenarios like saving game progress or undo functionality.

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Which Design Pattern is "Better"?

• If you need flexible object creation → Use Creational Patterns (Factory, Singleton, Builder).
• If you want better structure and scalability → Use Structural Patterns (Adapter, Decorator, Facade).
• If your focus is on behavior and communication between objects → Use Behavioral Patterns (Observer, Strategy, Command).

Conclusion

The best design pattern depends on your specific problem, scalability needs, and design goals. No single pattern is superior in all cases; instead, choosing the right pattern for the right problem is key to efficient software development.