What exactly is “interface based programming”?

Question

I often hear/read about interfaced based programming but I am not exactly clear on what that really means. Is interfaced based programming an actual stand alone topic that

Answer 1

Interface based programming can be thought of as decoupling the implementation of functionality and how you access the functionality.

You define an interface
interface ICallSomeone { public bool DialNumber(string number); }

and you write your implementation

public class callsomeone: ICallSomeone {
public bool DialNumber(string number) {
//dial number, return results }}

You use the interface without caring about the implementation. If you change the implementation, nothing cares because it just uses the interface.

Answer 2

Chapter 6 of "Practical API Design" by Jaroslav Tulach is titled "Code Against Interfaces, Not Implementations". It explains that, by coding against an interface rather than a specific implementation, you can decouple modules (or components) in a system and therefore raise the system quality.

Bertrand Meyer in OOSC2 explains clearly why "closing" a system and making it more modular raises its quality.