Encapsulation & Abstraction

Two concepts that go together in the object oriented approach are Encapsulation & Abstraction. Abstraction is the representation of only the essential features of an object, while Encapsulation is the hiding of the non-essential features.

Think of a person driving a car. He does not need to know the internal working of the engine or the way gear changes work, to be able to drive the car (Encapsulation). Instead, he needs to know things such as how much turning the steering wheel needs, etc (Abstraction).

Consider the example from the programmer’s perspective who wants to allow the user to add items to a list. The user only needs to click a button to add an item (Abstraction). The mechanism of how the item is added to the list is not essential for him (Encapsulation).

Below is a graphical representation of Encapsulation for the car class.



Implementing Encapsulation & Abstraction
Consider the countless advertisements being bombarded to viewers. The viewer does not listen to each one of them, rather only those he’s curious about. We use access specifiers to restrict the scope (visibility) of the class members.

Types of Access Specifiers

• public - The members (Functions & Variables) declared as public can be accessed from anywhere.
  
• private - Private members cannot be accessed from outside the class. This is the default access specifier for a member, i.e if you do not specify an access specifier for a member (variable or function), it will be private. Therefore, string PhoneNumber; is equivalent to private string PhoneNumber;
  
• protected - Protected members can be accessed only from the child classes.
  
• internal - Internal members can be accessed from anywhere within the application. This is the default access specifier for a class.
  
  Both these classes are equivalent.
  
  
  CODE
  class MyClass
  {
  
  }
  
  
  
  CODE
  internal class MyClass
  {
  
  }
  
  
• protected internal - Similar to protected, protected internal members can be accessed from the child classes but only within the application.

Note: The members are always accessible to its own member functions, irrespective of the access specifier.

Lets see an example:-



Lets study the code. Inside the main function we declare an object TheBlackHouse of the House class. Thereafter, we set the value of the data member DrawingRoom for TheBlackHouse to "Main Drawing Room". Since, DrawingRoom is declared as public, the above step works without any error. On the next line, TheBlackHouse.Kitchen = "Main Kitchen"; we are trying to assign the value "Main Kitchen" to the Kitchen variable of TheBlackHouse object. However, Kitchen is declared as private. Hence, this step generates an error.

In the next line, we are trying to call the private method EnterDrawingRoom for the object. This generates an error as well. Finally, we are calling the EnterKitchen function which is declared as public. Notice that inside the EnterKitchen function, we are assigning the value "The Kitchen" to the private variable Kitchen. This does not generate an error because the EnterKitchen method belongs to the same class and it has access to all the members inside the class, irrespective of the access specifier.

Why do we need Encapsulation & Abstraction?

Programming is all about concepts, different from coding where we basically translate the logic to language specific codes. When given a problem statement, there might be a number of ways to solve it. The logic devised to solve it will depend of the programmer. What we must learn to implement is the most efficient approach; efficient in terms of time, memory & cost. Object oriented methodologies such as these are what allow us to maintain efficiency.

By using encapsulation & abstraction, we reduce complexity by ignoring unimportant details and we maintain effectiveness by representing important ones.

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This post has been edited by turbopowerdmaxsteel: Jun 9 2007, 04:12 AM