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Essentially, encapsulation prevents external code from being concerned with the internal workings of an object. Encapsulation allows developers to present a consistent interface that is independent of its internal implementation. As one example, encapsulation can be used to hide the values or state of a structured data object inside a class.
Object composition is about combining objects within compound objects, and at the same time, ensuring the encapsulation of each object by using their well-defined interface without visibility of their internals. In this regard, object composition differs from data structures, which do not enforce encapsulation.
Data encapsulation, also known as data hiding, is the mechanism whereby the implementation details of a class are kept hidden from the user. The user can only perform a restricted set of operations on the hidden members of the class by executing special functions commonly called methods to prevent attributes of objects from being easily viewed and accessed.
Encapsulation prevents users from breaking the invariants of the class, which is useful because it allows the implementation of a class of objects to be changed for aspects not exposed in the interface without impact to user code. The definitions of encapsulation focus on the grouping and packaging of related information rather than security ...
For example, if a three-dimensional point (x, y, z) is represented in a program with three floating-point scalar variables and later, the representation is changed to a single array variable of size three, a module designed with information hiding in mind would protect the remainder of the program from such a change.
In these cases, no code blocks are created for validation, preprocessing or synthesis. These simplified accessors still retain the advantage of encapsulation over simple public instance variables, but it is common that, as system designs progress, the software is maintained and requirements change, the demands on the data become more ...
Liskov's notion of a behavioural subtype defines a notion of substitutability for objects; that is, if S is a subtype of T, then objects of type T in a program may be replaced with objects of type S without altering any of the desirable properties of that program (e.g. correctness).
In these languages, data and methods to manipulate the data are in the same code unit called an object. This encapsulation ensures that the only way that an object can access data is via methods of the object that contains the data. Thus, an object's inner workings may be changed without affecting code that uses the object.