Glossary

Every concept in this sheet, plus the smaller terms it uses. Select a concept to open its card.

Abstraction, interfaces and abstract classes: Abstraction exposes what something does and hides how.

Classes and objects: A class is a blueprint that bundles data (fields) with behaviour (methods).
Code review: Code review is another engineer reading a change before it merges, checking correctness, readability, tests and design, and leaving comments the author responds to.
Commits and commit messages: A commit is a saved snapshot of your project with a message.
Composition over inheritance: Composition builds behaviour by holding other objects ("has a") instead of inheriting from them ("is a").

Debugging: Debugging is finding why code behaves wrongly: read the error and stack trace, reproduce the bug reliably, form a guess, and check it with a debugger, breakpoints or targeted prints.

Encapsulation: Encapsulation hides an object's internal state and exposes only methods that keep it valid, using private fields or naming conventions like a leading underscore.
Exceptions and error handling: An exception signals that something went wrong, such as a missing file.

Inheritance: Inheritance lets a subclass reuse and extend a parent class, forming an "is a" relationship, such as SavingsAccount extending BankAccount.

Merging, conflicts and rebase: git merge combines branches with a merge commit.

Polymorphism: Polymorphism means one interface, many implementations: calling shape.area() runs the right method for a circle or a square.

SDLC and Agile: The software development life cycle covers requirements, design, build, test, release and maintenance.
SOLID principles: Five design guidelines: single responsibility, open for extension but closed for modification, Liskov substitution, interface segregation and dependency inversion.

Undoing mistakes in Git: git restore discards file edits, git commit --amend fixes the last local commit, git revert undoes a pushed commit with a new one, and git reflog finds commits you thought were lost.
Unit and integration tests: Unit tests check one function or class in isolation.