What s the difference between abstraction and encapsulation

Question

In interviews I have been asked to explain the difference between abstraction and encapsulation   My answer has been along the lines of   Abstraction allows us to represent complex real world in simplest manner  It is the process of identifying the relevant qualities and behaviors an object should possess  in other words  to represent the necessary feature without representing the background details  Encapsulation is a process of hiding all the internal details of an object from the outside real world  The word  encapsulation   is like  enclosing  into a  capsule   It restricts clients from seeing its internal view where the behavior of the abstraction is implemented    I think with above answer the interviewer was convinced  but then I was asked  if the purpose of both is hiding  then why there is a need to use encapsulation   At that time I didn t have a good answer for this   What should I have added to make my answer more complete

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My opinion of abstraction is not in the sense of hiding implementation or background details   Abstraction gives us the benefit to deal with a representation of the real world which is easier to handle  has the ability to be reused  could be combined with other components of our more or less complex program package  So we have to find out how we pick a complete peace of the real world  which is complete enough to represent the sense of our algorithm and data  The implementation of the interface may hide the details but this is not part of the work we have to do for abstracting something   For me most important thing for abstraction is    reduction of complexity reduction of size quantity splitting of non related domains to clear and independent components   All this has for me nothing to do with hiding background details   If you think of sorting some data  abstraction can result in    a sorting algorithm  which is independent of the data representation a compare function  which is independent of data and sort algorithm a generic data representation  which is independent of the used algorithms   All these has nothing to do with hiding information

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The essential thing about abstraction is that client code operates in terms of a different logical abstract model   That different model may be more or less complex than the implementation happens to be in any given client usage   For example   Iterator  abstracts  aka generalises  sequenced traversal of 0 or more values - in C   it manifests as begin      - gt   dereferencing   end    pre post    and possibly --  then there s            std  advance etc    That s a lot of baggage if the client could say increment a size t along an array anyway   The essential thing is that the abstraction allows client code that needs to perform such a traversal to be decoupled from the exact nature of the  container  or data source providing the elements   Iteration is a higher-level notion that sometimes restricts the way the traversal is performed  e g  a forward iterator can only advance an element at a time   but the data can then be provided by a larger set of sources  e g  from a keyboard where there s not even a  container  in the sense of concurrently stored values    The client code can generally switch to another data source abstracted through its own iterators with minimal or even no changes  and even polymorphically to other data types - either implicitly or explicitly using something like std  iterator traits lt Iterator gt   value type available   This is quite a different thing from encapsulation  which is the practice of making some data or functions less accessible  such that you know they re only used indirectly as a result of operations on the public interface   Encapsulation is an essential tool for maintaining invariants on an object  which means things you want to keep true after every public operation - if client code could just reach in and modify your object then you can t enforce any invariants   For example  a class might wrap a string  ensuring that after any operation any lowercase letters were changed to upper case  but if the client code can reach in and put a lowercase letter into the string without the involvement of the class s member functions  then the invariant can t be enforced   To further highlight the difference  consider say a private std  vector lt Timing Sample gt  data member that s incidentally populated by operations on the containing object  with a report dumped out on destruction   With the data and destructor side effect not interacting with the object s client code in any way  and the operations on the object not intentionally controlling the time-keeping behaviour  there s no abstraction of that time reporting functionality but there is encapsulation   An example of abstraction would be to move the timing code into a separate class that might encapsulate the vector  make it private  and just provide a interface like add const Timing Sample amp   and report std  ostream amp   - the necessary logical abstract operations involved with using such instrumentation  with the highly desirable side effect that the abstracted code will often be reusable for other client code with similar functional needs

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As far as iOS is concerned  it can be said that Objective C files  i e   h and  m  use abstraction as well as encapsulation   Abstraction  Header file   h  only exposes the functions and public members to outside world  No one knows how they are used unless they have the implementation file with them  It is the  m file that holds all the usage and implementation logic with it self   Implementation remains unexposed    Encapsulation  The property   property  encapsulates the memory management attribute  atomic  strong  retain  weak  of an iVar

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A program has mainly two parts   DATA and PROCESS  abstraction hides data in process so that no one can change  Encapsulation hides data everywhere so that it cannot be displayed  I hope this clarifies your doubt

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Abstraction  In case of an hardware abstraction layer  you have simple interfaces to trigger the hardware  e g  turn enginge left right  without knowing the hardware details behind  So hiding the complexity of the system  It s a simplified view of the real world   Encapsulation  Hiding of object internals  The object is an abstraction of the real world  But  the details of this object  like data structures     can be hidden via encapsulation

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I know there are lot s of answers before me with variety of examples  Well here is my opinion abstraction is getting interested from reality   In abstraction we hide something to reduce the complexity of it and In encapsulation we hide something to protect the data  So we define encapsulation as wrapping of data and methods in single entity referred as class  In java we achieve encapsulation using getters and setters not just by wrapping data and methods in it  we also define a way to access that data  and while accessing data we protect it also   Techinical e g would be to define a private data variable call weight Now we know that weight can t be zero or less than zero in real world scenario  Imagine if there are no getters and setters someone could have easily set it to a negative value being public member of class  Now final difference using one real world example  Consider a circuit board consisting of switches and buttons  We wrap all the wires into a a circuit box  so that we can protect someone by not getting in contact directly encapsulation   We don t care how those wires are connected to each other we just want an interface to turn on and off switch  That interface is provided by buttons abstraction

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In my view encapsulation is a thought of programmer to hide the complexity of the program code by using access specifier  Where as Abstraction is separation of method and object  according to there function and behavior  For example Car has sheets  wheels  break  headlight

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Abstraction refers to the act of representing essential features without including the background details or explanations   Encapsulation is a technique used for hiding the properties and behaviors of an object and allowing outside access only as appropriate  It prevents other objects from directly altering or accessing the properties or methods of the encapsulated object   Difference between abstraction and encapsulation  1 Abstraction focuses on the outside view of an object  i e  the interface  Encapsulation  information hiding  prevents clients from seeing it   s inside view  where the behavior of the abstraction is implemented   2 Abstraction solves the problem in the design side while Encapsulation is the Implementation   3 Encapsulation is the deliverable of Abstraction  Encapsulation barely talks about grouping up your abstraction to suit the developer needs

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Abstraction  Exposing the Entity instead of the details of the entity    Details are there  but we do not consider them  They are not required    Example 1   Various calculations  Addition  Multiplication  Subtraction  Division  Square  Sin  Cos  Tan   We do not show the details of how do we calculate the Sin  Cos or Tan  We just Show Calculator and it s various Methods which will be  and which needs to be used by the user   Example 2   Employee has  First Name  Last Name  Middle Name  He can Login    Logout    DoWork     Many processes might be happening for Logging employee In  such as connecting to database  sending Employee ID and Password  receiving reply from Database  Although above details are present  we will hide the details and expose only  Employee    Encapsulation  Enclosing  Treating multiple characteristics  functions as one unit instead of individuals  So that outside world will refer to that unit instead of it s details directly    Details are there  we consider them  but do not show them  instead we show what you need to see    Example 1   Instead of calling it as Addition  Subtraction  Multiplication  Division  Now we will call it as a Calculator   Example 2   All characteristics and operations are now referred by the employee  such as  John   John Has name  John Can DoWork    John can Login     Hiding  Hiding the implemention from outside world  So that outside world will not see what should not be seen    Details are there  we consider them  but we do not show them  You do not need to see them    Example 1   Your requirement  Addition  Substraction  Multiplication  Division  You will be able to see it and get the result    You do not need to know where operands are getting stored  Its not your requirement    Also  every instruction that I am executing  is also not your requirement   Example 2   John Would like to know his percentage of attendance  So GetAttendancePercentage   Will be called   However  this method needs data saved in database  Hence it will call FetchDataFromDB    FetchDataFromDB   is NOT required to be visible to outside world    Hence we will hide it  However  John GetAttendancePercentage   will be visible to outside world   Abstraction  encapsulation and hiding complement each others   Because we create level of abstraction over details  the details are encapsulated  And because they are enclosed  they are hidden

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Difference between Abstraction and Encapsulation  -  Abstraction   Abstraction solves the problem in the design level  Abstraction is used for hiding the unwanted data and giving relevant data  Abstraction lets you focus on what the object does instead of how it does it  Abstraction- Outer layout  used in terms of design  For Example - Outer Look of a Mobile Phone  like it has a display screen and keypad buttons to dial a number    Encapsulation   Encapsulation solves the problem in the implementation level  Encapsulation means hiding the code and data into a single unit to protect the data from outside world  Encapsulation means hiding the internal details or mechanics of how an object does something  Encapsulation- Inner layout  used in terms of implementation  For Example - Inner Implementation detail of a Mobile Phone  how keypad button and Display Screen are connect with each other using circuits

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In my opinion  both terms are related in some sense and sort of mixed into each other   Encapsulation  provides a way to grouping related fields  methods in a class  or module  to wrap the related things together  As of that time  it provides data hiding in two ways    Through access modifiers    Purely for hiding state of the class object  Abstracting some functionalities   a     Through interfaces abstract classes  complex logic inside the encapsulated class or module can be abstracted generalized to be used by outside   b  Through function signatures  Yes  even function signatures example of abstracting  Because callers only knows the signature and parameters  if any  and know nothing about how the function is carried out  It only cares of returned value    Likewise   Abstraction  might be think of a way of encapsulation in terms of grouping wrapping the behaviour into an interface  or abstract class or might be even a normal class

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Abstraction   Abstraction is process in which you collect or gather relevant data and remove non-relevant data   And if you have achieved abstraction  then encapsulation also achieved     Encapsulation  Encapsulation is a process in which you wrap of functions and members in a single unit  Means You are hiding the implementation detail  Means user can access by making object of class  he she can t see detail    Example     public class Test          int t      string  s   public void show          s    Testing      Console WriteLine s      Console WriteLine See        No error       int See          t   10     return t        public static void Main         Test obj    new Test      obj Show       there is no error   obj See       Error - Inaccessible due to its protection level          In the above example  User can access only Show   method by using obj  that is Abstraction    And See   method is calling internally in Show   method that is encapsulation  because user doesn t know what things are going on in Show   method

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Abstraction has to do with separating interface from implementation    We don t care what it is  we care that it works a certain way    Encapsulation has to do with disallowing access to or knowledge of internal structures of an implementation    We don t care or need to see how it works  only that it does    Some people do use encapsulation as a synonym for abstraction  which is  IMO  incorrect   It s possible that your interviewer thought this   If that is the case then you were each talking about two different things when you referred to  encapsulation      It s worth noting that these concepts are represented differently in different programming languages   A few examples    In Java and C   interfaces  and  to some degree  abstract classes  provide abstraction  while access modifiers provide encapsulation  It s mostly the same deal in C    except that we don t have interfaces  we only have abstract classes  In JavaScript  duck typing provides abstraction  and closure provides encapsulation    Naming convention can also provide encapsulation  but this only works if all parties agree to follow it

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Encapsulation is used for 2 main reasons   1   Data hiding  amp  protecting  the user of your class can t modify the data except through your provided methods    2   Combining the data and methods used to manipulate the data together into one entity  capsule   I think that the second reason is the answer your interviewer wanted to hear   On the other hand  abstraction is needed to expose only the needed information to the user  and hiding unneeded details  for example  hiding the implementation of methods  so that the user is not affected if the implementation is changed

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Its Simple   Take example of television - it is Encapsulation  because    Television is loaded with different functionalies that i don t know because they are completely hidden  Hidden things like music  video etc everything bundled in a capsule that what we call a TV   Now  Abstraction is When we know a little about something and which can help us to manipulate something for which we don t know how it works internally   For eg  A remote-control for TV is abstraction  because   With remote we know that pressing the number keys will change the channels  We are not aware as to what actually happens internally  We can manipulate the hidden thing but we don t know how it is being done internally    Programmatically  when we can acess the hidden data somehow and know something   is Abstraction    And when we know nothing about the internals its Encapsulation   Without remote we can t change anything on TV we have to see what it shows coz all controls are hidden

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Abstraction  Hiding the data  Encapsulation  Binding the data

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ABSTRACTION  A view of a problem that extracts the essential information     relevant to a particular purpose and ignores the remainder of     the information   IEEE  1983   ENCAPSULATION   Encapsulation or equivalently information hiding refers to the     practice of including within an object everything it needs  and     furthermore doing this in such a way that no other object need ever     be aware of this internal structure

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Abstraction is one of the many benefits of Data Encapsulation  We can also say Data Encapsulation is one way to implement Abstraction

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Encapsulation   Suppose I have some confidential documents  now I hide these documents inside a locker so no one can gain access to them  this is encapsulation   Abstraction   A huge incident took place which was summarised in the newspaper  Now the newspaper only listed the more important details of the actual incident  this is abstraction  Further the headline of the incident highlights on even more specific details in a single line  hence providing higher level of abstraction on the incident  Also highlights of a football cricket match can be considered as abstraction of the entire match   Hence encapsulation is hiding of data to protect its integrity and abstraction is highlighting more important details   In programming terms we can see that a variable may be enclosed is the scope of a class as private hence preventing it from being accessed directly from outside  this is encapsulation  Whereas a a function may be written in a class to swap two numbers  Now the numbers may be swapped in either by either using a temporary variable or through bit manipulation or using arithmetic operation  but the goal of the user is to receive the numbers swapped irrespective of the method used for swapping  this is abstraction

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Developer A  who is inherently utilising the concept of abstraction will use a module library function widget  concerned only with what it does  and what it will be used for  but not how it does it  The interface of that module library function widget  the  levers  the Developer A is allowed to pull push  is the personification of that abstraction    Developer B  who is seeking to create such a module function widget will utilise the concept of encapsulation to ensure Developer A  and any other developer who uses the widget  can take advantage of the resulting abstraction  Developer B is most certainly concerned with how the widget does what it does   TLDR     Abstraction - I care about what something does  but not how it does it  Encapsulation - I care about how something does what it does such that others only need to care about what it does      As a loose generalisation  to abstract something  you must encapsulate something else  And by encapsulating something  you have created an abstraction

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Simply put  abstraction is all about making necessary information for interaction with the object  visible  while encapsulation enables a developer to implement the desired level of abstraction

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Why Encapsulation  Why Abstraction   lets start with the question below   1 What happens if we allow code to directly access field    directly allowing means making field public   lets understand this with an example   following is our BankAccount class and following is its limitation  Limitation Policy    Balance in BankAccount can not be more than 50000Rs   This line   is very important to understand   class BankAccount        public   double balanceAmount     Following is   AccountHolder   user of BankAccount  class which is consumer of    BankAccount   class   class AccountHolder      BankAccount mybankAccount   new BankAccount        DoAmountCreditInBankAccount               mybankAccount balanceAmount   70000                    this is invalid practice because this statement violates policy    Here         BankAccount class is not able to protect its field from direct access        Reason for direct access by acount holder is that balanceAmount directly         accessible due to its public access modifier  How to solve this issue and         successfully implement BankAccount Policy Limitation                     if some other part of code directly access balanceAmount field and set balance amount to 70000Rs which is not acceptable  Here in this case we can not prevent some other part of code from accessing balanceAmount field   So what we can do      Answer is we can make balanceAmount field private so that no other code can directly access it and allowing access to that field only via public method which operates on balanceAmount field  Main role of method is that we can write some prevention logic inside method so that field can not be initialized with more than 50000Rs  Here we are making binding between data field called balanceAmount and method which operates on that field  This process is called Encapsulation  it is all about protecting fields using access modifier such as private   Encapsulation is one way to achieve abstraction    but How     User of this method will not know about implementation  How amount gets credited  logic and all that stuff  of method which he she will invoke  Not knowing about implementation details by user is called Abstraction Hiding details from user    Following will be the implementation of class   class BankAccount        private   double balanceAmount        public   void UpdateBankBalance double amount           if balanceAmount   amount  gt  50000               Console WriteLine  Bank balance can not be more than 50000  Transaction can                            not be proceed              else              balanceAmount   balanceAmount   amount             Console WriteLine  Amount has been credited to your bank account                                successfully                        class AccountHolder      BankAccount mybankAccount   new BankAccount        DoAmountCreditInBankAccount              mybankAccount UpdateBankBalance some amount                   mybankAccount balanceAmount will not be accessible due to its protection level         directly from AccountHolder so account holder will consume BankAccount public         method UpdateBankBalance double amount  to update his her balance

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Encapsulation  Encapsulation from what you have learnt googling around  is a concept of combining the related data and operations in a single capsule or what we could say a class in OOP  such that no other program can modify the data it holds or method implementation it has  at a particular instance of time  Only the getter and setter methods can provide access to the instance variables   Our code might be used by others and future up-gradations or bug fixes are liable  Encapsulation is something that makes sure that whatever code changes we do in our code doesn t break the code of others who are using it   Encapsulation adds up to the maintainability  flexibility and extensibility of the code   Encapsulation helps hide the implementation behind an interface   Abstraction  Abstraction is the process of actually hiding the implementation behind an interface  So we are just aware of the actual behavior but not how exactly the think works out internally  The most common example could the scenario where put a key inside the lock and easily unlock it  So the interface here is the keyhole  while we are not aware of how the levers inside the lock co-ordinate among themselves to get the lock unlocked   To be more clear  abstraction can be explained as the capability to use the same interface for different objects  Different implementations of the same interface can exist  while the details of every implementation are hidden by encapsulation   Finally  the statement to answer all the confusions until now - The part that is hidden relates to encapsulation while the part that is exposed relates to abstraction   Read more on this here

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Encapsulation is basically denying the access to the internal implementation or knowledge about internals to the external world  while Abstraction is giving a generalized view of any implementation that helps the external world to interact with it

[oop] What's the difference between abstraction and encapsulation?

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