SOLID principles, including Single Responsibility Principle, Open/Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, and Dependency Inversion Principle, aim to enhance software design flexibility, maintainability, and extensibility. Each principle is detailed with explanations, code examples, and benefits. Following these principles leads to clearer, more concise code, easier testing and maintenance, reduced coupling between classes, improved code reusability, scalability, and stability. Embracing these principles results in enhanced code scalability, reduced risks of code modifications, decreased maintenance costs, increased system stability, inheritance consistency, code reliability, error propagation avoidance, and correct polymorphism implementation. The principles ensure client classes do not rely on unnecessary methods, improve code flexibility, reusability, clarity, and reduce system coupling. Implementing these principles brings advantages such as increased flexibility and code reusability, clearer and focused interfaces, reduced system coupling, and improved software architecture design.

本文介绍了三种常见的设计模式：单例模式（Singleton Pattern）、工厂模式（Factory Pattern）和观察者模式（Observer Pattern）。在单例模式中，实现了一个数据库连接池管理器，确保系统中只有一个连接池实例；工厂模式设计了一个文件处理系统，支持多种数据格式解析；观察者模式中实现了一个股票市场监控系统，能够通知注册的观察者股票价格变化。这些模式都采用了面向对象的设计思想，有助于提高系统的灵活性和可维护性。