Abstract classes

Abstract classes are a special type of base classes. These abstract class members are methods and properties declared without an implementation. All classes derived directly from abstract classes must implement these abstract methods and properties.

• Abstract is a keyword
• Whenever a class is not providing full functionality then it is need to be declared as abstract.
• A methods without body is called as abstract method
• Abstract method is also called as rule.
• When a class contains at least one abstract method then it must be declared as abstract class.
• Abstract methods must be override
• Abstract classes are not instantiable.(i.e. object cannot be created)
• Using abstract class we can create reference.
• Reference works based on child class memory.
• Abstract class provides as a set of rules(abstract methods),which need to be followed (override)by child class.

Program on abstract class
using System;
abstract  class abc
{
protected int l, b;
public void get(int x, int y)
{
l = x;
b = y;
}
public abstract void put();

}
class xyz:abc
{
public override void put()
{
Console.WriteLine("Area of rectange" + (l * b));
}     
}
class vision
{
public static void Main(String[] args)
{
xyz x = new xyz();
x.get(10, 5);
x.put();
}
}

Program on abstract classes and polymorphism.
using System;
abstract  class abc
{
protected int b,h;
public void get(int x, int y)
{
b = x;
h = y;
}
public abstract void put();

}
class xyz:abc
{

    public override void put()
{
Console.WriteLine("Area of Triangle" + (b*h)/2);
}     
}
class vision
{
public static void Main(String[] args)
{
xyz x = new xyz();
abc z;
z = x;       // polymorphisam
z.get(5, 3);
z.put();

       
}
}

Program to find the area of triangle, circle, simple interest using polymorphism.

using System;
abstract  class abc
{
protected int b,h;
public void get(int x, int y)
{
b = x;
h = y;
Console.WriteLine("Area of Triangle" + (b * h) / 2);
}
public abstract void put();

}
class xyz:abc
{
int r;
public xyz(int x)
{
r = x;
}

public override void put()
{
Console.WriteLine("Area of Circle" + (22 / 7 * r * r));
}     
}
class pqr:abc
{
int p,t,r;
public pqr(int x,int y,int z)
{
p=x;
t=y;
r=z;
}
public override void put()
{
Console.WriteLine("Simple Interest" + (p * t * r) / 100);

    }
}
class vision
{
public static void Main(String[] args)
{
xyz x = new xyz(5);
pqr y = new pqr(1000,5,3);
abc z;
z = x;       // polymorphisam
z.get(4, 5);
z.put();
z = y;
z.put();

    }
}