Abstraction vs Encapsulation in Java

Question

Possible Duplicate    Abstraction VS Information Hiding VS Encapsulation       I know this question might have been asked thousands times on this forum  even net is also filled with lots of definitions about these concepts but all sounds same and all uses same technical words  For example following definitions  Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity  This keeps the data safe from outside interface and misuse  One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper   What I understood from above definition is that creating variables  mark them private and generate getter-setter for those variables and use object to access those getter and setter  In that way data is hidden inside object and is only accessible through object  Hope I am right     Abstraction is the process in Java which is used to hide certain details and only show the essential features of the object  In other words  it deals with the outside view of an object  interface     Now this is the part which confuses me always  Whenever I think about abstraction the thing which comes to my mind is Abstract class may be because both have Abstract keyword   Above definition says abstraction means hiding data and only showing required details but that is what we are already doing in encapsulation right  then what is the difference  Also I did not get what is out side view of object in it deals with the outside view of an object   Can someone please put more light on this with some real life example or with some programmatic examples if possible

User · Answer

Abstraction is about identifying commonalities and reducing features that you have to work with at different levels of your code   e g   I may have a Vehicle class  A Car would derive from a Vehicle  as would a Motorbike  I can ask each Vehicle for the number of wheels  passengers etc  and that info has been abstracted and identified as common from Cars and Motorbikes   In my code I can often just deal with Vehicles via common methods go    stop   etc  When I add a new Vehicle type later  e g  Scooter  the majority of my code would remain oblivious to this fact  and the implementation of Scooter alone worries about Scooter particularities

User · Answer

In simple words  You do abstraction when deciding what to implement  You do encapsulation when hiding something that you have implemented

User · Answer

OO Abstraction occurs during class level design  with the objective of hiding the implementation complexity of how the the features offered by an API   design   system were implemented  in a sense simplifying the  interface  to access the underlying implementation    The process of abstraction can be repeated at increasingly  higher  levels  layers  of classes  which enables large systems to be built without increasing the complexity of code and understanding at each layer   For example  a Java developer can make use of the high level features of FileInputStream without concern for how it works  i e  file handles  file system security checks  memory allocation and buffering will be managed internally  and are hidden from consumers    This allows the implementation of FileInputStream to be changed  and as long as the API  interface  to FileInputStream remains consistent  code built against previous versions will still work   Similarly  when designing your own classes  you will want to hide internal implementation details from others as far as possible   In the Booch definition1  OO Encapsulation is achieved through Information Hiding  and specifically around hiding internal data  fields   members representing the state  owned by a class instance  by enforcing access to the internal data in a controlled manner  and preventing direct  external change to these fields  as well as hiding any internal implementation methods of the class  e g  by making them private     For example  the fields of a class can be made private by default  and only if external access to these was required  would a get   and or set    or Property  be exposed from the class   In modern day OO languages  fields can be marked as readonly   final   immutable which further restricts change  even within the class    Example where NO information hiding has been applied  Bad Practice    class Foo         BAD - NOT Encapsulated - code external to the class can change this field directly       Class Foo has no control over the range of values which could be set     public int notEncapsulated      Example where field encapsulation has been applied   class Bar         Improvement - access restricted only to this class    private int encapsulatedPercentageField         The state of Bar  and its fields  can now be changed in a controlled manner    public void setEncapsulatedField int percentageValue          if  percentageValue  gt   0  amp  amp  percentageValue  lt   100              encapsulatedPercentageField   percentageValue                   else throw     out of range          Example of immutable   constructor-only initialization of a field   class Baz      private final int immutableField      public void Baz int onlyValue                 As above  can also check that onlyValue is valid       immutableField   onlyValue             Further change of  immutableField  outside of the constructor is NOT permitted  even within the same class      Re   Abstraction vs Abstract Class  Abstract classes are classes which promote reuse of commonality between classes  but which themselves cannot directly be instantiated with new   - abstract classes must be subclassed  and only concrete  non abstract  subclasses may be instantiated  Possibly one source of confusion between Abstraction and an abstract class was that in the early days of OO  inheritance was more heavily used to achieve code reuse  e g  with associated abstract base classes   Nowadays  composition is generally favoured over inheritance  and there are more tools available to achieve abstraction  such as through Interfaces  events   delegates   functions  traits   mixins etc   Re   Encapsulation vs Information Hiding  The meaning of encapsulation appears to have evolved over time  and in recent times  encapsulation can commonly also used in a more general sense when determining which methods  fields  properties  events etc to bundle into a class   Quoting Wikipedia      In the more concrete setting of an object-oriented programming language  the notion is used to mean either an information hiding mechanism  a bundling mechanism  or the combination of the two    For example  in the statement      I ve encapsulated the data access code into its own class      the  interpretation of encapsulation is roughly equivalent to the Separation of Concerns or the Single Responsibility Principal  the  S  in SOLID   and could arguably be used as a synonym for refactoring      1  Once you ve seen Booch s encapsulation cat picture you ll never be able to forget encapsulation - p46 of Object Oriented Analysis and Design with Applications   2nd Ed

[java] Abstraction vs Encapsulation in Java

Examples related to java

Examples related to oop

Examples related to concept