Overview of Design Patterns

• Creational Patterns: Focus on object creation mechanisms, controlling how objects are instantiated.
• Structural Patterns: Deal with class and object composition, simplifying relationships and improving flexibility.
• Behavioral Patterns: Manage communication and responsibilities between objects, coordinating workflows and interactions.

Examples of Design Patterns

Creational Patterns

• Singleton: Ensures a class has only one instance, e.g., a Logger class used across an application.

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• Factory Method: Provides an interface for creating objects but allows subclasses to decide which class to instantiate, e.g., a document editor creating different document types.
• Abstract Factory: Creates families of related objects without specifying their concrete classes, e.g., UI components for different operating systems.
• Builder: Constructs complex objects step by step, e.g., building a customizable meal or report.
• Prototype: Creates new objects by cloning existing ones, useful for performance optimization.
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Structural Patterns

• Adapter: Converts one interface into another expected by clients, e.g., integrating legacy APIs with modern systems.
• Decorator: Adds responsibilities to objects dynamically without altering their structure, e.g., adding features to a text editor.
• Facade: Provides a simplified interface to a complex subsystem, e.g., a unified API for multiple payment gateways.
• Composite: Treats individual objects and compositions uniformly, e.g., a file system with files and directories.
• Proxy: Controls access to another object, e.g., lazy loading or access control.

Behavioral Patterns

• Observer: Defines a one-to-many dependency, e.g., a notification system where multiple subscribers receive updates.
• Strategy: Encapsulates interchangeable algorithms, e.g., different payment methods in an e-commerce platform.
• Command: Encapsulates requests as objects, e.g., implementing undo/redo functionality.
• Chain of Responsibility: Passes requests along a chain of handlers, e.g., processing support tickets.
• Template Method: Defines the skeleton of an algorithm, allowing subclasses to override steps, e.g., a data processing pipeline.

Real-World Applications

• Logger: Singleton ensures a single logging instance across the system.

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• Payment Gateway: Strategy pattern allows switching between credit card, PayPal, or cryptocurrency payments.

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• Notification System: Observer pattern notifies multiple users of events like messages or alerts.

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• Undo/Redo Feature: Command pattern manages reversible actions in applications like text editors.

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• API Integration: Facade pattern simplifies complex third-party API interactions.

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  These patterns are widely used in enterprise applications, SaaS platforms, and game development, helping developers write clean, maintainable, and scalable code while adhering to best practices. For hands-on examples in multiple programming languages, resources like Refactoring.Guru provide detailed code illustrations in Java, Python, C#, and more.

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