Friday, May 22, 2009

Abstract Class in OOPs

Hi,

i find so many times developers confusing with the term Abstract or abstraction in OOPS. Here's a perfect description and definition of abstraction in OOPs. Hope it will help u better understanding of Abstract and OOPs.

Abstraction
Abstraction is another good feature of OOPS. Abstraction means to show only the necessary details to the client of the object. Do you know the inner details of the Monitor of your PC? What happen when you switch ON Monitor? Does this matter to you what is happening inside the Monitor? No Right, Important thing for you is weather Monitor is ON or NOT. When you change the gear of your vehicle are you really concern about the inner details of your vehicle engine? No but what matter to you is that Gear must get changed that’s it!! This is abstraction; show only the details which matter to the user.
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, Right?
So abstraction says expose only the details which are concern with the user (client) of your object. So the client who is using your class need not to be aware of the inner details like how you class do the operations? He needs to know just few details. This certainly helps in reusability of the code.
As I have generally seen developers are not very much comfortable with the database programming. Let’s say you are designing a class that is used to interact with the database and to perform some of database operations. Now client of your class need not to be aware of database programming, he just need to be aware of some of the details of your class and easily can perform the database operations exposed by your class without deep knowledge of database programming.
The best thing of abstract is that this decouples the user of the object and its implementation. So now object is easy to understand and maintain also. As if there is any change in the process of some operation. You just need to change the inner details of a method, which have no impact on the client of class.



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Abstraction means that you have some class that is more common than others that extend it. By example, if you have classes Triangle and Rectangle:
class Triangle
{
public double a;
public double b;
public double c;

public double Area
{
get { return triangle's area }
}
}

class Rectangle
{
public double a;
public double b;

public double Area
{
get { return rectangle's area }
}
}
These classes have something in common - they have property called Area plus also sides (a and b) but I don't see any reason to make sides abstract. Let's add also Circle and we have no point of sides at all. Now let's generalize these classes and let's create one more common class called Shape. Also, let's make it abstract class so this class cannot be created separately - it can be created only through extending.
public abstract class Shape
{
public double Area();
}
And now let's write previous classes so they extend Shape class.
class Triangle : Shape
{
public double a;
public double b;
public double c;

public double Area
{
get { return triangle's area }
}
}

class Rectangle : Shape
{
public double a;
public double b;

public double Area
{
get { return rectangle's area }
}
}
So, what's the win, you may ask? Okay, not of these classes use Shape as their base class. So does Circle. In the context where we don 't care about specific properties of object we can handle all extended objects as Shape. By example, let's calculate total area of Shapes in list.
List shapes = ListShapes() // contains circles, triangles and rectangles
double area = 0;

foreach(Shape shape in shapes)
area += shape.Area;

// do something useful with area here
Without extending Shape class we should write separate loop for each shape type. And also we have to have separate methods to get different types of shapes. Now we had only one method to list shapes and one loop to handle them as one - we didn't cared about lengths of sides or radiuses or any other specific properties. Same way you can make many other abstractions. By example, you can add coordinates to Shape class if shape's positioning is required.




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Abstraction in the object oriented world generalizes the characteristics and behaviours. The following classes describe this

public class Mammal

{

public string m_color; // Abstract Charactersistic 1

public string m_height; // Abstract Charactersistic 2

public string m_weight; // Abstract Charactersistic 1

public Mammal()

{

}

public void Move()

{

// Abstract behaviour

}

}

// Elephant is a Mammal hence it extends abstract class Mammal

public class Elephant : Mammal

{

public string m_color = "gray"; // Gray color

public int m_height = 120; // 10 feet or 120 inches

public int m_weight = 1500; // 1500 pounds

public Elephant()

{

}

public void Move()

{

// Implement the Elephant Walks Behaviour

}

}

// A whale is also a mammal hence it extends the Mammal class

public class Whale: Mammal

{

public string m_color = "darkgray"; // Dark Gray color

public int m_height = 60; // 5 feet or 60 inches

public int m_weight = 2000; // 2000 pounds

public Whale()

{

}

public void Move()

{

// Implement the way a Whale swims

}

}

1 comment:

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