Interfaces and Implementations

Let’s split this into two parts: the interface (the "what") and the implementation (the "how").

• Interface: Think of an interface as a menu at a restaurant. It lists what dishes are available (methods), but not how they’re cooked.
• Implementation: If the interface is the restaurant menu, the implementation is the kitchen actually cooking your order. It’s the grunt work – the Java class that does what the interface promised.

Why Does This Matter?

• Flexibility: Swap implementations without breaking code (e.g., switch from hardcoded data to a database later).
• Testing: Ease of mock the interface to test other components.
• Clarity: Separates “what” from “how” for cleaner code. Real implementations get messy – that’s why we hide them behind clean interfaces
• Spring Boot automatically injects the right "kitchen" when you order a "dish" (this is called Dependency injection).