Welcome to the Design Patterns Repository! This repository serves as a comprehensive guide to object-oriented design patterns, with examples and explanations that will help developers understand, implement, and apply these patterns to real-world projects. By following this repository, you will learn how design patterns can improve code reusability, scalability, and maintainability while addressing common challenges in software engineering.
- What Are Design Patterns?
- Creational Design Patterns
- Structural Design Patterns
- Behavioral Design Patterns
- Dependency Injection
- Exception Handling Patterns
- Summary of Applications
- Build Instructions
- Resources
- Conclusion
Design patterns are proven solutions to recurring software design problems. They provide templates for solving issues related to object creation, composition, and communication. Design patterns are categorized into three main types:
- Creational Patterns: Deal with object creation.
- Structural Patterns: Focus on organizing classes and objects.
- Behavioral Patterns: Concerned with object collaboration and responsibilities.
By using design patterns, developers can:
- Write reusable and maintainable code.
- Enhance software flexibility and scalability.
- Improve communication within development teams through a shared vocabulary.
Purpose: Ensures that a class has only one instance and provides a global access point to it.
Key Features:
- Controlled access to the sole instance.
- Thread-safe implementations.
- Lazy initialization for resource efficiency.
Example Use Cases:
- Configuration managers.
- Logging utilities.
Purpose: Extends Singleton by allowing multiple instances, identified by unique keys.
Key Features:
- Combines Singleton benefits with multi-instance management.
- Provides centralized control over instances.
Example Use Cases:
- Caching.
- Resource pools.
Purpose: Defines an interface for creating objects but lets subclasses decide the type of object to instantiate.
Key Features:
- Promotes loose coupling.
- Simplifies object creation logic.
Example Use Cases:
- UI frameworks.
- Plugin architectures.
Purpose: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
Key Features:
- Ensures consistency among products.
- Encapsulates object creation.
Example Use Cases:
- Cross-platform UI libraries.
Purpose: Constructs complex objects step by step.
Key Features:
- Separates construction from representation.
- Enables incremental construction.
Example Use Cases:
- Generating reports.
- Building HTML or JSON structures.
Purpose: Creates new objects by copying existing ones.
Key Features:
- Cloning instead of instantiation.
- Reduces overhead for expensive creation.
Example Use Cases:
- Game object cloning.
- Resource duplication.
Purpose: Dynamically adds responsibilities to an object.
Key Features:
- Promotes open-closed principle.
- Reduces inheritance complexity.
Example Use Cases:
- GUI elements.
- Data transformation pipelines.
Purpose: Converts one interface into another expected by clients.
Key Features:
- Enables interoperability.
- Facilitates legacy code integration.
Example Use Cases:
- Adapting third-party libraries.
Purpose: Decouples abstraction from implementation.
Key Features:
- Supports independent variation.
- Simplifies complex hierarchies.
Example Use Cases:
- Graphics rendering systems.
Purpose: Composes objects into tree structures to represent part-whole hierarchies.
Key Features:
- Simplifies client code.
- Uniform treatment of objects.
Example Use Cases:
- File systems.
- UI frameworks.
Purpose: Provides a surrogate or placeholder for another object.
Key Features:
- Controls access.
- Adds functionality like caching or logging.
Example Use Cases:
- Remote proxies.
- Lazy initialization.
Purpose: Minimizes memory usage by sharing common data among objects.
Key Features:
- Reduces memory overhead.
- Facilitates large-scale object management.
Example Use Cases:
- Text editors.
- Game engines.
Purpose: Encapsulates algorithms and makes them interchangeable.
Key Features:
- Adheres to the open-closed principle.
- Reduces code duplication.
Example Use Cases:
- Payment processing systems.
- Sorting algorithms.
Purpose: Defines a one-to-many dependency between objects.
Key Features:
- Supports event-driven programming.
- Loose coupling between subjects and observers.
Example Use Cases:
- Notification systems.
- MVC frameworks.
Purpose: Encapsulates requests as objects.
Key Features:
- Enables undo/redo functionality.
- Decouples sender and receiver.
Example Use Cases:
- Text editors.
- Task queues.
Purpose: Allows an object to change its behavior when its state changes.
Key Features:
- Simplifies complex state management.
- Promotes single-responsibility principle.
Example Use Cases:
- Workflow systems.
Purpose: Passes requests along a chain of handlers.
Key Features:
- Decouples sender and receiver.
- Adds flexibility to request processing.
Example Use Cases:
- Event bubbling in GUIs.
Purpose: Provides a way to access elements in a collection without exposing its underlying structure.
Key Features:
- Simplifies traversal logic.
- Promotes encapsulation.
Example Use Cases:
- Database cursors.
Purpose: Reduces communication complexity by centralizing object interactions.
Key Features:
- Facilitates decoupled communication.
- Simplifies collaboration.
Example Use Cases:
- Chat systems.
Purpose: Captures an object’s state for later restoration.
Key Features:
- Encapsulates state without exposing internals.
- Enables undo functionality.
Example Use Cases:
- Game save systems.
Purpose: Defines the skeleton of an algorithm, allowing subclasses to fill in the details.
Key Features:
- Promotes code reuse.
- Enforces algorithm consistency.
Example Use Cases:
- Frameworks.
Purpose: Separates operations from the object structure.
Key Features:
- Simplifies adding new operations.
- Adheres to the open-closed principle.
Example Use Cases:
- Compilers.
Purpose: Reduces tight coupling by providing dependencies from the outside.
Key Features:
- Simplifies testing.
- Improves maintainability.
Example Use Cases:
- Inversion of Control (IoC) containers.
Purpose: Handles unexpected errors gracefully.
Key Features:
- Structured error handling.
- Resource cleanup.
Example Use Cases:
- Logging frameworks.
- Resilient systems.
This repository showcases design patterns in various contexts:
- Creational Patterns: Simplify object creation.
- Structural Patterns: Organize and optimize system structure.
- Behavioral Patterns: Enhance object collaboration.
Use Maven for building and running the code:
mvn compile
mvn exec:java
mvn test
mvn package
mvn clean- Design Patterns: Elements of Reusable Object-Oriented Software by the Gang of Four.
- Online courses and documentation.
Mastering design patterns is essential for crafting high-quality software. This repository serves as a guide to understanding and applying these patterns effectively in real-world projects.
Happy coding! 🚀