In object-oriented programming (OOP), encapsulation refers to the bundling of data with the methods that operate on that data, or the restricting of direct access to some of an object's components.[1] Encapsulation is used to hide the values or state of a structured data object inside a class, preventing direct access to them by clients in a way that could expose hidden implementation details or violate state invariance maintained by the methods. Show
This mechanism is not unique to OOP. Implementations of abstract data types, e.g., modules, offer a similar form of encapsulation. The similarity has been explained by programming language theorists in terms of existential types.[2] Meaning[edit]In object-oriented programming languages, and other related fields, encapsulation refers to one of two related but distinct notions, and sometimes to the combination thereof:[3][4]
Some programming language researchers and academics use the first meaning alone or in combination with the second as a distinguishing feature of object-oriented programming, while some programming languages that provide lexical closures view encapsulation as a feature of the language orthogonal to object orientation. The second definition is motivated by the fact that in many object-oriented languages, and other related fields, the components are not hidden automatically and this can be overridden; thus, information hiding is defined as a separate notion by those who prefer the second definition. The features of encapsulation are supported using classes in most object-oriented languages, although other alternatives also exist. Encapsulation and inheritance[edit]The authors of Design Patterns discuss the tension between inheritance and encapsulation at length and state that in their experience, designers overuse inheritance. They claim that inheritance often breaks encapsulation, given that inheritance exposes a subclass to the details of its parent's implementation.[8] As described by the yo-yo problem, overuse of inheritance and therefore encapsulation, can become too complicated and hard to debug. Information hiding[edit]Under the definition that encapsulation "can be used to hide data members and member functions", the internal representation of an object is generally hidden from view outside of the object's definition. Typically, only the object's own methods can directly inspect or manipulate its fields. Hiding the internals of the object protects its integrity by preventing users from setting the internal data of the component into an invalid or inconsistent state. A supposed benefit of encapsulation is that it can reduce system complexity, and thus increase robustness, by allowing the developer to limit the interdependencies between software components.[citation needed] Some languages like
Smalltalk and Ruby only allow access via object methods, but most others (e.g., C++,
C#, Delphi or Java) offer the programmer a degree of control over what is hidden, typically via keywords like Almost always, there is a way to override such protection – usually via reflection API (Ruby, Java, C#, etc.), sometimes by mechanism like name mangling
(Python), or special keyword usage like Examples[edit]Restricting data fields[edit]Languages like C++, C#, Java, PHP, Swift, and Delphi offer ways to restrict access to data fields. Below is an example in C# that shows how access to a data field can be restricted through the use of a class Program { public class Account { private decimal accountBalance = 500.00m; public decimal CheckBalance() { return this.accountBalance; } } static void Main() { Account myAccount = new Account(); decimal myBalance = myAccount.CheckBalance(); /* This Main method can check the balance via the public * "CheckBalance" method provided by the "Account" class * but it cannot manipulate the value of "accountBalance" */ } } Below is an example in Java: public class Employee { private BigDecimal salary = new BigDecimal(50000.00); public BigDecimal getSalary() { return this.salary; } public static void main() { Employee e = new Employee(); BigDecimal sal = e.getSalary(); } } Encapsulation is also possible in non-object-oriented languages. In C, for example, a structure can be declared in the public API via the header file for a set of functions that operate on an item of data containing
data members that are not accessible to clients of the API with the // Header file "api.h" struct Entity; // Opaque structure with hidden members // API functions that operate on 'Entity' objects extern struct Entity * open_entity(int id); extern int process_entity(struct Entity *info); extern void close_entity(struct Entity *info); // extern keywords here are redundant, but don't hurt. // extern defines functions that can be called outside the current file, the default behavior even without the keyword Clients call the API functions to allocate, operate on, and deallocate objects of an opaque data type. The contents of this type are known and accessible only to the implementation of the API functions; clients cannot directly access its contents. The source code for these functions defines the actual contents of the structure: // Implementation file "api.c" #include "api.h" struct Entity { int ent_id; // ID number char ent_name[20]; // Name ... and other members ... }; // API function implementations struct Entity * open_entity(int id) { ... } int process_entity(struct Entity *info) { ... } void close_entity(struct Entity *info) { ... } Name mangling[edit]Below is an example of Python, which does not support variable access restrictions. However, the convention is that a variable whose name is prefixed by an underscore should be considered private.[11] class Car: def __init__(self) -> None: self._maxspeed = 200 def drive(self) -> None: print(f"Maximum speed is {self._maxspeed}.") redcar = Car() redcar.drive() # This will print 'Maximum speed is 200.' redcar._maxspeed = 10 redcar.drive() # This will print 'Maximum speed is 10.' See also[edit]
References[edit]
What is an abstract data type quizlet?Abstract Data Types. A specification for a group of values and the operations on those values that is defined conceptually and independently of any programming language. Defining ADT in an interface.
What is the combining of data and code in a single object known as?Encapsulation refers to the combining of data and code into a single object.
What is the default access for members of the class abstract data type?1. Later, we will discuss protected members that are accessible to derived classes. This access level, however, is rarely used. With the class keyword, the default access level is private.
Which of the following is automatically called when an object is destroyed?A destructor is a member of a function which is automatically called when the class is destroyed.
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