How abstraction and encapsulation differ

Question

I am preparing for an interview and decided to brush up my OOP concepts  There are hundreds of articles available  but it seems each describes them differently  Some says     Abstraction is  the process of identifying common patterns that have   systematic variations  an abstraction represents the common pattern   and provides a means for specifying which variation to use   Richard   Gabriel     and is achieved through abstract classes   Some other says     Abstraction means to show only the necessary details to the client of   the object   and     Let   s say you have a method  CalculateSalary  in your Employee class    which takes EmployeeId as parameter and returns the salary of the   employee for the current month as an integer value  Now if someone   wants to use that method  He does not need to care about how Employee   object calculates the salary  An only thing he needs to be concern is   name of the method  its input parameters and format of resulting   member    I googled again and again and none of the results seem to give me a proper answer   Now  where does encapsulation fit in all these  I searched and found a stack overflow question  Even the answers to that questions were confusing Here  it says     Encapsulation is a strategy used as part of abstraction  Encapsulation   refers to the state of objects - objects encapsulate their state and   hide it from the outside  outside users of the class interact with it   through its methods  but cannot access the classes state directly  So   the class abstracts away the implementation details related to its   state    And here another reputed member says      They are different concepts       Abstraction is the process of refining away all the   unneeded unimportant attributes of an object and keep only the   characteristics best suitable for your domain    Now I m messed up with the whole concept  I know about abstract class  inheritance  access specifiers and all  I just want to know how should I answer when I am asked about abstraction and or encapsulation in an interview   Please don t mark it as a duplicate  I know there are several similar questions  But I want to avoid the confusion among the conflicting explanations  Can anyone suggest a credible link  A link to stackoverflow question is also welcome unless it creates confusion again      EDIT  I need answers  a bit c  oriented

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I think of it this way  encapsulation is hiding the way something gets done   This can be one or many actions    Abstraction is related to  why  I am encapsulating it the first place     I am basically telling the client  You don t need to know much about how I process the payment and calculate shipping  etc   I just want you to tell me you want to  Checkout  and I will take care of the details for you    This way I have encapsulated the details by generalizing  abstracting  into the Checkout request   I really think that abstracting and encapsulation go together

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Below is a semester long course distilled in a few paragraphs   Object-Oriented Analysis and Design  OOAD  is actually based on not just two but four principles  They are    Abstraction  means that you only incorporate those features of an entity which are required in your application  So  if every bank account has an opening date but your application doesn t need to know an account s opening date  then you simply don t add the OpeningDate field in your Object-Oriented Design  of the BankAccount class      Abstraction in OOAD has nothing to do with abstract classes in OOP   Per the principle of Abstraction  your entities are an abstraction of what they are in the real world  This way  you design an abstraction of Bank Account down to only that level of detail that is needed by your application  Inheritance  is more of a coding-trick than an actual principle  It saves you from re-writing those functionalities that you have written somewhere else  However  the thinking is that there must be a relation between the new code you are writing and the old code you are wanting to re-use  Otherwise  nobody prevents you from writing an Animal class which is inheriting from BankAccount  even if it is totally non-sensical   Just like you may inherit your parents  wealth  you may inherit fields and methods from your parent class  So  taking everything that parent class has and then adding something more if need be  is inheritance  Don t go looking for inheritance in your Object Oriented Design  Inheritance will naturally present itself  Polymorphism  is a consequence of inheritance  Inheriting a method from the parent is useful  but being able to modify a method if the situation demands  is polymorphism  You may implement a method in the subclass with exactly the same signature as in parent class so that when called  the method from child class is executed  This is the principle of Polymorphism  Encapsulation  implies bundling the related functionality together and giving access to only the needful  Encapsulation is the basis of meaningful class designing in Object Oriented Design  by    putting related data and methods together  and  exposing only the pieces of data and methods relevant for functioning with external entities       Another simplified answer is here         People who argue that  Abstraction of OOAD results in the abstract keyword of OOP     Well that is incorrect   Example  When you design a University in an application using object oriented principles  you only design an  abstraction  of the university  Even though there is usually one cash dispensing ATM in almost every university  you may not incorporate that fact if it s not needed for your application  And now though you have designed only an abstraction of the university  you are not required to put abstract in your class declaration  Your abstract design of university will be a normal class in your application

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One example has always been brought up to me in the context of abstraction  the automatic vs  manual transmission on cars  The manual transmission hides some of the workings of changing gears  but you still have to clutch and shift as a driver  Automatic transmission encapsulates all the details of changing gears  i e  hides it from you  and it is therefore a higher abstraction of the process of changing gears

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my 2c  the purpose of encapsulation is to hide implementation details from the user of your class e g  if you internally keep a std  list of items in your class and then decide that a std  vector would be more effective you can change this without the user caring  That said  the way you interact with the either stl container is thanks to abstraction  both the list and the vector can for instance be traversed in the same way using similar methods  iterators

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As I knowit  encapsulation is hiding data of classes in themselves  and only making it accessible via setters   getters  if they must be accessed from the outer world   Abstraction is the class design for itself   Means  how You create Your class tree  which methods are general ones  which  are  inherited  which can be overridden which attributes are only on private level  or on protected  how Do You build up Your class inheritance tree  Do You use final classes  abtract classes  interface-implementation   Abstraction is more placed the oo-design phase  while encapsulation also enrolls into developmnent-phase

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Image source  Abstraction  is outlined by the top left and top right images of the cat  The surgeon and the old lady designed  or visualized  the animal differently  In the same way  you would put different features in the Cat class  depending upon the need of the application  Every cat has a liver  bladder  heart and lung  but if you need your cat to  purr  only  you will abstract your application s cat to the design on top-left rather than the top-right   Encapsulation  is outlined by the cat standing on the table  That s what everyone outside the cat should see the cat as  They need not worry whether the actual implementation of the cat is the top-left one or the top-right one or even a combination of both     PS  Go here on this same question to hear the complete story

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Abstraction  In Java  abstraction means hiding the information to the real world  It establishes the contract between the party to tell about    what should we do to make use of the service      Example  In API development  only abstracted information of the service has been revealed to the world rather the actual implementation  Interface in java can help achieve this concept very well   Interface provides contract between the parties  example  producer and consumer  Producer produces the goods without letting know the consumer how the product is being made  But  through interface  Producer let all consumer know what product can buy  With the help of abstraction  producer can markets the product to their consumers   Encapsulation   Encapsulation is one level down of abstraction  Same product company try shielding information from each other production group  Example  if a company produce wine and chocolate  encapsulation helps shielding information how each product Is being made from each other    If I have individual package one for wine and another one for chocolate  and if all the classes are declared in the package as default access modifier  we are giving package level encapsulation for all classes  Within a package  if we declare each class filed  member field  as private and having a public method to access those fields  this way giving class level encapsulation to those fields

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I will try to demonstrate Encapsulation and Abstraction in a simple way   Lets see     The wrapping up of data and functions into a single unit  called class  is known as encapsulation  Encapsulation containing and hiding information about an object  such as internal data structures and code    Encapsulation is -   Hiding Complexity  Binding Data and Function together   Making Complicated Method s Private  Making Instance Variable s Private  Hiding Unnecessary Data and Functions from End User    Encapsulation implements Abstraction   And Abstraction is -    Showing Whats Necessary  Data needs to abstract from End User    Lets see an example-  The below Image shows a GUI of  Customer Details to be ADD-ed into a Database      By looking at the Image we can say that we need a Customer Class   Step - 1  What does my Customer Class needs   i e         2 variables to store Customer Code and Customer Name    1 Function to Add the Customer Code and Customer Name into Database         namespace CustomerContent              public class Customer                     public string CustomerCode                  public string CustomerName                  public void ADD                                my DB code will go here                Now only ADD method wont work here alone   Step -2  How will the validation work  ADD Function act   We will need Database Connection code and Validation Code  Extra Methods         public bool Validate                Granular Customer Code and Name     return true               public bool CreateDBObject                DB Connection Code     return true           class Program      static void main String   args            CustomerComponent Customer obj   new CustomerComponent Customer        obj CustomerCode    s001        obj CustomerName    Mac         obj Validate         obj CreateDBObject          obj ADD              Now there is no need of showing the Extra Methods Validate    CreateDBObject    Complicated and Extra method    to the End User End user only needs to see and know about Customer Code  Customer Name and ADD button which will ADD the record   End User doesn t care about HOW it will ADD the Data to Database    Step -3  Private the extra and complicated methods which doesn t involves End User s Interaction   So making those Complicated and Extra method as Private instead Public i e Hiding those methods  and deleting the obj Validate    obj CreateDBObject    from main in class Program we achieve Encapsulation   In other words Simplifying Interface to End User is Encapsulation   So now the complete code looks like as below -   namespace CustomerContent         public class Customer                public string CustomerCode               public string CustomerName                public void ADD                          my DB code will go here                    private bool Validate                          Granular Customer Code and Name            return true                     private bool CreateDBObject                          DB Connection Code            return true                class Program          static void main String   args                 CustomerComponent Customer obj   new CustomerComponent Customer           obj CustomerCode    s001            obj CustomerName    Mac            obj ADD             Summary    Step -1  What does my Customer Class needs  is Abstraction   Step -3  Step -3  Private the extra and complicated methods which doesn t involves End User s Interaction is Encapsulation   P S  - The code above is hard and fast    UPDATE  There is an video on this link to explain the sample  What is the difference between Abstraction and Encapsulation

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Encapsulation  hiding data using getters and setters etc   Abstraction  hiding implementation using abstract classes and interfaces etc

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Abstraction means to show only the necessary details to the client of the object   Actually that is encapsulation  also see the first part of the wikipedia article in order to not be confused by encapsulation and data hiding  http   en wikipedia org wiki Encapsulation  object-oriented programming   keep in mind that by simply hiding all you class members 1 1 behind properties is not encapsulation at all  encapsulation is all about protecting invariants and hiding of implementation details   here a good article about that  http   blog ploeh dk 2012 11 27 Encapsulationofproperties  also take a look at the articles linked in that article   classes  properties and access modifiers are tools to provide encapsulation in c    you do encapsulation in order to reduce complexity      Abstraction is  the process of identifying common patterns that have systematic variations  an abstraction represents the common pattern and provides a means for specifying which variation to use   Richard Gabriel     Yes  that is a good definition for abstraction       They are different concepts    Abstraction is the process of refining away all the unneeded unimportant attributes of an object and keep only the characteristics best suitable for your domain    Yes  they are different concepts  keep in mind that abstraction is actually the opposite of making an object suitable for YOUR domain ONLY  it is in order to make the object suitable for the domain in general   if you have a actual problem and provide a specific solution  you can use abstraction to formalize a more generic solution that can also solve more problems that have the same common pattern  that way you can increase the re-usability for your components or use components made by other programmers that are made for the same domain  or even for different domains   good examples are classes provided by the  net framework  for example list or collection  these are very abstract classes that you can use almost everywhere and in a lot of domains  Imagine if  net only implemented a EmployeeList class and a CompanyList that could only hold a list of employees and companies with specific properties  such classes would be useless in a lot of cases  and what a pain would it be if you had to re-implement the whole functionality for a CarList for example  So the  List  is ABSTRACTED away from Employee  Company and Car  The List by itself is an abstract concept that can be implemented by its own class   Interfaces  abstract classes or inheritance and polymorphism are tools to provide abstraction in c    you do abstraction in order to provide reusability

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Abstraction and Encapsulation are confusing terms and dependent on each other   Let s take it by an example   public class Person               private int Id   get  set            private string Name   get  set            private string CustomName                         return  Name -     Name     and Id is -     Id                    When you created Person class  you did encapsulation by writing properties and functions together Id  Name  CustomName   You perform abstraction when you expose this class to client as  Person p   new Person    p CustomName      Your client doesn t know anything about Id and Name in this function   Now if  your client wants to know the last name as well without disturbing the function call  You do encapsulation by adding one more property into Person class like this   public class Person                       private int Id   get  set                private string Name   get  set                private string LastName  get  set               public string CustomName                                 return  Name -     Name     and Id is -     Id    last name -     LastName                            Look  even after addding an extra property in class  your client doesn t know what you did to your code  This is where you did abstraction

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I think they are slightly different concepts  but often they are applied together  Encapsulation is a technique for hiding implementation details from the caller  whereas abstraction is more a design philosophy involving creating objects that are analogous to familiar objects processes  to aid understanding  Encapsulation is just one of many techniques that can be used to create an abstraction   For example  take  windows   They are not really windows in the traditional sense  they are just graphical squares on the screen  But it s useful to think of them as windows  That s an abstraction   If the  windows API  hides the details of how the text or graphics is physically rendered within the boundaries of a window  that s encapsulation

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Encapsulation  Hiding implementation details  NOTE  data AND OR methods  such that only what is sensibly readable writable usable by externals is accessible to them  everything else is  untouchable  directly   Abstraction  This sometimes refers specifically to a type that cannot be instantiated and which provides a template for other types that can be  usually via subclassing  More generally  abstraction  refers to making having something that is less detailed  less specific  less granular   There is some similarity  overlap between the concepts but the best way to remember it is like this  Encapsulation is more about hiding the details  whereas abstraction is more about generalizing the details

[c#] How abstraction and encapsulation differ?

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