Design Patterns Tutorial

Design Patterns Tutorialoverview

Design patterns are common, reusable solutions to specific problems in software development. They are best practices summarized from experience, helping developers design more flexible, maintainable, and scalable software systems. This tutorial will give you a comprehensive understanding of design patterns core concepts, classification, principles, and implementation and application scenarios of various common design patterns.

What are Design Patterns?

Design patterns are a set of repeatedly used, classified and summarized code design experiences that solve specific problems in specific environments. Design patterns are not ready-made code, but a way of thinking and method to solve problems. It describes under what circumstances how to construct code structure to solve specific design problems.

Design Patterns Classification

Design patterns are usually divided into three main categories:

1. Creational Patterns

Creational patterns focus on the object creation process, providing a way to hide creation logic when creating objects, making code more flexible and maintainable. Common creational patterns include:

• singleton pattern (Singleton)
• factory pattern (Factory Method)
• abstractionfactory pattern (Abstract Factory)
• Builder Pattern
• Prototype Pattern

2. Structural Patterns

Structural patterns focus on the composition of classes and objects, implementing new functions through inheritance and composition, making systems more flexible and scalable. Common structural patterns include:

• adapter pattern (Adapter)
• decorator pattern (Decorator)
• Proxy Pattern
• Composite Pattern
• Facade Pattern
• Bridge Pattern
• Flyweight Pattern

3. Behavioral Patterns

Behavioral patterns focus on communication and responsibility allocation between objects, defining interaction methods between objects, making systems more flexible and maintainable. Common behavioral patterns include:

• observer pattern (Observer)
• strategy pattern (Strategy)
• Template Method Pattern
• Command Pattern
• Iterator Pattern
• State Pattern
• Visitor Pattern
• Mediator Pattern
• Memento Pattern
• Interpreter Pattern
• Chain of Responsibility Pattern

Design Patterns Principles

Design patterns are based on some core object-oriented design principles, which are the foundation of design patterns:

1. Single Responsibility Principle

A class should have only one reason to change, meaning a class should be responsible for only one responsibility.

2. Open-Closed Principle

Software entities (classes, modules, functions, etc.) should be open for extension, closed for modification.

3. Liskov Substitution Principle

Subclasses should be able to replace their parent classes without affecting program correctness.

4. Interface Segregation Principle

Clients should not depend on interfaces they don't use; large interfaces should be split into smaller, more specific interfaces.

5. Dependency Inversion Principle

High-level modules should not depend on low-level modules; both should depend on abstractions; abstractions should not depend on details, details should depend on abstractions.