Oo

OO, commonly shorthand for object-oriented programming, is a programming paradigm that organizes software as a collection of objects. An object encapsulates data in attributes and behavior in methods, while a class defines the structure and capabilities its objects share. Programs are composed by creating object instances and having them interact through message passing and method calls.

Core concepts include encapsulation, which hides internal state; abstraction, which exposes a simplified interface; inheritance, enabling new classes to derive from existing ones; and polymorphism, allowing objects to be treated according to their base type while exhibiting specialized behavior. Many languages also support composition as an alternative to inheritance for building complex functionality.

OO originated with Simula in the 1960s and was popularized by Smalltalk. The approach gained broad adoption in the 1980s and 1990s with languages such as C++, Java, and later C#, Python, and Ruby. Over time, OO became a dominant paradigm in software development, though it coexists with other approaches in multi-paradigm languages.

Design and practice: OO supports modeling of real-world concepts and fosters modularity and code reuse. However, deep inheritance hierarchies can create tight coupling and fragility; modern OO design often emphasizes composition over inheritance and the use of interfaces or abstract classes to define contracts.

Criticism and alternatives: Some critics argue that OO can lead to complexity and boilerplate. Many modern languages are multi-paradigm, mixing OO with functional and procedural styles, and some domains are better served by other approaches such as functional or data-oriented designs.

Examples of languages that support OO include Java, C++, Python, C#, Ruby, Objective-C, Kotlin, and others, each with varying emphasis on class-based design, interfaces, and metaprogramming. See also object-oriented design, inheritance, and polymorphism.