Revision Notes/SOLID Principles
Field Entry - SOLID Principles
Dependency Inversion Principle (DIP)
High-level modules should not depend on low-level modules — both should depend on abstractions (interfaces).
Field Note - Real-world Analogy
“Like wall power sockets. Your laptop (high-level module) plugs into a power socket (abstraction/interface). It doesn't care if the power comes from a coal plant, solar panels, or a generator (low-level implementations). Both the laptop and the power source depend on the socket standard — neither depends on each other directly.”
Field Observations - Key Topics Covered
Without DIP, high-level business logic directly uses low-level details: OrderService creates a new MySQLDatabase() and calls methods on it. Now OrderService is tightly coupled to MySQL. If you want to switch to PostgreSQL, or use an in-memory database for testing, you have to change OrderService.
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