Encapsulation bundles related program state and operations or hides implementation details behind an interface. Encapsulation in object-oriented programming realizes this through objects and their permitted operations; encapsulation also applies to modules outside object-oriented programs.
The useful boundary is a promise: clients request operations through an API, and the implementation maintains a representation invariant. Instead of proving that every client updates several storage fields consistently, prove that the permitted operations preserve the representation invariant. Information hiding also leaves room to replace the data structure while keeping the client-facing behavior, a property called representation independence.
Bundling state and operations alone does not establish that promise. Representation exposure can let clients bypass the API. A
private annotation alone is not a security guarantee: it does not establish correctness of operations, isolation from hostile code or safe handling of shared mutable storage. The examples below concern sequential calls with no concurrent access and no client access to internal storage; they do not claim protection against arbitrary memory modification. Articles by others on the same topic
Encapsulation is a fundamental principle of object-oriented programming (OOP) that involves bundling the data (attributes) and methods (functions) that operate on that data into a single unit called a class. It also restricts direct access to some of the object's components, which is a means of preventing accidental interference and misuse of the methods and data.