Object-Oriented Programming is a paradigm that organizes software design around objects rather than functions and logic, bundling data with methods that operate on that data. It emerged in the 1960s and became mainstream through languages like Smalltalk, C++, Java, and Python, fundamentally changing how developers structure reusable, maintainable code. At its core, OOP is built on four foundational pillars—encapsulation, inheritance, polymorphism, and abstraction—that together enable modeling real-world problems as interacting objects. Understanding when to favor composition over inheritance, how generics provide type-safe reuse, and recognizing common anti-patterns like God Objects are crucial for writing clean, scalable object-oriented systems.
What This Cheat Sheet Covers
This topic spans 21 focused tables and 152 indexed concepts, 146 flashcards, 7 practice tests with 195 questions. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
A jump-to index of every table row in this cheat sheet.
An interactive map of every table and concept in this topic.
Table 1: Core Concepts
The vocabulary every object-oriented language shares, no matter the syntax. Once the gap between a class and an instance clicks, and you can see how the four pillars, encapsulation, inheritance, polymorphism, and abstraction, each solve a different problem, the rest of OOP reads as variations on these few ideas.
| Concept | Example | Description | |
|---|---|---|---|
class Dog: def __init__(self, name): self.name = name | • Blueprint or template that defines structure and behavior for objects • contains attributes (data) and methods (functions). | ||
my_dog = Dog("Rex")my_dog.name | • Concrete realization of a class • an individual entity with its own state created from the class blueprint. | ||
class Account: def __init__(self): self.__balance = 0 | Bundling data and methods into a single unit (class) while hiding internal implementation details from outside access. | ||
class Puppy(Dog): def __init__(self, name, age): super().__init__(name) | • Mechanism where a class derives properties and behavior from another class • creates "is-a" relationships (e.g., Puppy is a Dog). | ||
def make_sound(animal): animal.speak() | • Ability for objects of different types to respond to the same method call • enables treating related objects uniformly through a common interface. | ||
class Shape: def area(self): pass | • Process of exposing only essential features while hiding implementation complexity • focuses on what an object does rather than how. | ||
def bark(self): print("Woof!") | • Function defined inside a class that describes behaviors objects can perform • operates on object data. | ||
self.name = nameself.age = 5 | • Variable bound to an object or class that stores state or data • can be instance-specific or shared across all instances. | ||
dog.bark()account.deposit(100) | • Core OOP communication mechanism where objects send messages (method calls) to each other to trigger behavior • keeps objects decoupled. |