Also known as: object-oriented programming "OOP"

Object-oriented programming (OOP) is a paradigm that bundles state and the behaviour that acts on it into objects — units that combine fields (data) with methods (functions that operate on that data).¹

An object hides its data behind methods, and shared interfaces let callers treat different types uniformly.

Core ideas

OOP rests on a few pillars. Encapsulation hides an object’s internal data behind a clean interface, the foundation of abstraction and information hiding. Inheritance derives specialised types from general ones, and polymorphism lets you treat different types uniformly through a shared interface — calling area() without knowing whether the object is a circle or a square.¹ These combine to keep coupling low: callers depend on a contract, not a concrete class.

When it fits

OOP shines when a problem decomposes naturally into “things” with identity and lifecycle — a User, a Connection, a tuned Receiver. Languages such as Java, C#, Ruby, and Python support it strongly. Most of the Gang of Four design patterns are expressed in object-oriented terms.

Trade-offs

Critics note that overusing inheritance creates rigid, tangled hierarchies, which is why modern OOP leans on composition (“has-a”) over deep inheritance (“is-a”).¹ Many languages are multi-paradigm: the same codebase can mix object-oriented structure with functional transformations and imperative inner loops, choosing the style that fits each part of the problem.

Sources

1. Object-oriented programming — Wikipedia, for the definition, the pillars (encapsulation, inheritance, polymorphism), and the composition-over-inheritance guidance. ↩ ↩² ↩³

See also

• Functional programming
• Imperative programming
• Abstraction
• Coupling & cohesion
• Design patterns
• Java
• C#
• Ruby

Learn it step by step

• Paradigms & language families