The abstract classes are base classes.The abstract classes are always having child classes.The abstract classes doesn't having instance variables.The abstract classes having reference variables.
Example on Abstract Class:
abstract class Dept1
{
protected int sal;
public void eSal()
{
sal=5000;
}
public abstract void tSal();
}
class Dept2:Dept1
{
int bonus;
public override void tSal()
{
bonus=500;
int ts=sal+bonus;
MessageBox.Show(ts.toString());
}
}
private void button1_click()
{
dept2 obj=new Dept2();
obj.eSal();
obj.tSal();
}