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The SOLID design principles are a set of guidelines for creating maintainable, flexible, and extensible software. These principles, which include Single Responsibility, Open-Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion, help developers craft loosely coupled and highly cohesive modules.
Consider a banking application that processes transactions. By applying the Single Responsibility Principle, we can separate the concerns of transaction processing, account management, and user authentication into distinct classes. This ensures that each class has a single reason to change, making the codebase more maintainable.
The Open-Closed Principle suggests that classes should be open for extension but closed for modification. In our banking application, we can define an abstract base class for transactions and extend it for specific transaction types like deposits and withdrawals. This allows us to add new transaction types without modifying existing code.
Liskov Substitution ensures that derived classes can be used interchangeably with their base classes. If we have a generic “Account” class and specific subclasses like “SavingsAccount” and “CheckingAccount,” we should be able to use them interchangeably without affecting the correctness of the program.
Interface Segregation advises splitting large interfaces into smaller, more focused ones. Instead of having a single monolithic interface for all banking operations, we can define separate interfaces for account management, transaction processing, and reporting. This allows clients to depend only on the interfaces they need, reducing coupling.