Stage 1 · Lesson 3 of 8
Abstraction and interfaces
means showing callers what something does while hiding how. An is the tool for it: a named list of methods that any class can promise to provide. Checkout code can ask a PaymentGateway to charge an amount without knowing whether a card, a wallet or a test fake is behind it.
That is what lets you swap an implementation, or use a fake in a , without editing the caller. An is a partial class that can share code and fields between subclasses, but cannot be created on its own. Reach for an interface first and an abstract class only when there is real .
Common trapcreating an interface for every class by habit, even when only one implementation will ever exist.
A question to check yourself, an AI practice session and 2 cheat sheet entries come with the full roadmap. Unlock
Resources for this stage
Start with· follow one of these
- CoursePaidGrokking the Object Oriented Design Interview
Design Gurus · Intermediate · Subscription
Its opening chapters teach the four OOP ideas applied inside real designs, with UML and running code
- CourseFreeMIT 6.102: Software Construction
MIT · Intermediate
Free MIT readings: Abstract Data Types, Rep Invariants and Interfaces and Subtyping are this stage at university depth