�ݺ�ߣ

This document discusses the SOLID principles of object-oriented design: 1. Single responsibility principle - each class should have a single responsibility and only one reason to change. 2. Open-closed principle - code should be open for extension but closed for modification. New features can be added without changing existing code. 3. Liskov substitution principle - subclasses should be substitutable for their parent classes without errors occurring. 4. Interface segregation principle - large classes should define interfaces for groups of methods to decrease dependency. 5. Dependency inversion principle - classes should not create dependencies directly but use dependency injection through setters or constructors for flexibility.