Reader Level:
ARTICLE

Abstraction in C#

Posted by Faizan Ahmed Articles | Current Affairs October 13, 2010
The word abstract means a concept or an idea not associated with any specific instance.
  • 1
  • 0
  • 70007


Abstraction

The word abstract means a concept or an idea not associated with any specific instance.

In programming we apply the same meaning of abstraction by making classes not associated with any specific instance.

The abstraction is done when we need to only inherit from a certain class, but not need to instantiate objects of that class. In such case the base
class can be regarded as "Incomplete". Such classes are known as an "Abstract Base Class".

Abstract Base Class

There are some important points about Abstract Base Class :

  1. An Abstract Base class can not be instantiated; it means the object of that class can not be created.

  2. Class having abstract keyword and having, abstract keyword with some of its methods (not all) is known as an Abstract Base Class.

  3. Class having Abstract keyword and having abstract keyword with all of its methods is known as pure Abstract Base Class.

  4. The method of abstract class that has no implementation is known as "operation". It can be defined as abstract void method ();

  5. An abstract class holds the methods but the actual implementation of those methods is made in derived class.

Lets have a look of this code!

    abstract class animal
    {
        public abstract void eat();
        public void sound()
        {
            Console.WriteLine("dog can sound");
        }
    }
This is the Abstract Base Class, if I make both of its methods abstract then this class would become a pure Abstract Base Class.

Now we derive a class of 'dog' from the class animal.

    abstract class animal
    {
        public abstract void eat();
        public void sound()
        {
            Console.WriteLine("dog can sound");
        }
    }
    class dog : animal
    {
        public override void eat() { Console.WriteLine("dog can eat"); }
    }

Here you can see we have 2 methods in the Abstract Base Class, the method eat() has no implementation; that is why it is being declared as 'abstract' while the method sound() has its own body so it is not declared as 'abstract'.

In the derived class we have the same name method but this method has it's body.

We are doing abstraction here so that we can access the method of derived class without any trouble.

Let's have a look!

    class program
    {
        abstract class animal
        {
            public abstract void eat();
            public void sound()
            {
                Console.WriteLine("dog can sound");
            }
        }
        class dog : animal
        {
            public override void eat() { Console.WriteLine("dog can eat"); }
        }
        static void Main(string[] args)
        {
            dog mydog = new dog();
            animal thePet = mydog;
            thePet.eat();
            mydog.sound();
        }
    }

Finally we created an Object 'mydog' of class dog, but we didn't instantiate any object of Abstract Base Class 'animal'.

According to "Ivor Horton" (a programmer of Java) an object can not be instantiated, but we can declare a variable of the Abstract Class type. If this statement is true then it could be possible:

animal thePet;

This is an object which is declared as thePet and its data type is the abstract base class 'animal'.

We can use this Object to store Objects of the subclass.

In the above code we declare an Object 'thePet', of the type animal (the Abstract Base Class) and simply copied the object of another object (only the reference is copied as they belong to reference type). Now we can use object 'thePet' just as object 'mydog'.

The output of this code would be as

dog can eat
dog can sound

Conclusion:

l conclude here by saying that Abstraction is not a difficult job to do, but you need to be confident while performing abstraction. Our every new topic covers the all previous topics. In the abstraction the polymorphism is being covered and performed. The method overriding could be done by putting the keyword 'new' before that overridden method. Everything is possible in Programming and there are multiple ways to do a single job. Abstraction is one of the smart ways to do these kind of tasks.
 

Article Extensions
Contents added by sandeep sharma on Aug 25, 2012

public abstract class A

{

    // Class members here.

}

An abstract class cannot be instantiated. The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share. For example, a class library may define an abstract class that is used as a parameter to many of its functions, and require programmers using that library to provide their own implementation of the class by creating a derived class.

 

Abstract classes may also define abstract methods. This is accomplished by adding the keyword abstract before the return type of the method. For example:

 

public abstract class A

{

    public abstract void DoWork(int i);

}

Abstract methods have no implementation, so the method definition is followed by a semicolon instead of a normal method block. Derived classes of the abstract class must implement all abstract methods. When an abstract class inherits a virtual method from a base class, the abstract class can override the virtual method with an abstract method. For example:

 

// compile with: /target:library

public class D

{

    public virtual void DoWork(int i)

    {

        // Original implementation.

    }

}

 

public abstract class E : D

{

    public abstract override void DoWork(int i);

}

 

public class F : E

{

    public override void DoWork(int i)

    {

        // New implementation.

    }

}

If a virtual method is declared abstract, it is still virtual to any class inheriting from the abstract class. A class inheriting an abstract method cannot access the original implementation of the method—in the previous example, DoWork on class F cannot call DoWork on class D. In this way, an abstract class can force derived classes to provide new method implementations for virtual methods.

COMMENT USING

Trending up