Which statement best describes encapsulation in object-oriented design?

Which statement best describes encapsulation in object-oriented design?

• A. Public fields with no access control.
• B. Mutating internal state freely from outside.
• C. Directly exposing internal state via reflection.
• D. Encapsulate fields by making them private and expose behavior through public methods.

Answer: (D)

Encapsulation is about hiding the internal data of an object and controlling how that data is accessed or modified through a well-defined interface. In practice, you keep fields private and expose behavior via public methods. This lets the object enforce rules, validate inputs, preserve invariants, and change its internal representation later without breaking external code that relies on its behavior. For example, a class might store a balance as a private field and provide public methods like deposit and withdraw that enforce rules (such as not allowing a negative balance). Exposing internal state directly, whether by making fields public or by allowing external code to mutate state freely (or via reflection), would bypass those safeguards and break encapsulation.

Encapsulation is about hiding the internal data of an object and controlling how that data is accessed or modified through a well-defined interface. In practice, you keep fields private and expose behavior via public methods. This lets the object enforce rules, validate inputs, preserve invariants, and change its internal representation later without breaking external code that relies on its behavior. For example, a class might store a balance as a private field and provide public methods like deposit and withdraw that enforce rules (such as not allowing a negative balance). Exposing internal state directly, whether by making fields public or by allowing external code to mutate state freely (or via reflection), would bypass those safeguards and break encapsulation.