Inheritance (virtual, abstract, override)

public abstract class Account

{

private string name; // Only accessible in base class

protected double balance;// Accessible in base class and derived Class

//constructor to initialize these fields

public Account(string nm, double bal)

{

this.name = nm;

this.balance = bal;

}

//The virtual keyword means these methods can be overridden in derived classes:

public virtual void Credit(double amount)

{

this.balance += amount;

}

public virtual void Debit(double amount)

{

this.balance -= amount;

}

public virtual void Display()

{

Console.WriteLine("Name={0}, balance={1}", this.name,this.balance);

}

//this method is not marked as virtual, it cannot be overridden in derived classes.

//This method provides the capability to change the name of the account holder.

public void ChangeName(string newName)

{

this.name = newName;

}

//The abstract keyword means this method must be overridden in derived classes:

public abstract double CalculateBankCharge();

}

public class SavingsAccount : Account

{

private double minBalance;// If the balance drops below minBalance, the bank will charge a fee on the account

//Modify the SavingsAccount constructor to initialize the fields in the base class and in this class:

public SavingsAccount(string nm, double bal, double min)

: base(nm, bal)// Call base-class constructor first

{

minBalance = min; // Then initialize fields in this class

}

//These methods override the virtual methods inherited from the base class:

public override void Debit(double amount)

{

if (amount <= balance) // Use balance, inherited from base class

base.Debit(amount); // Call Debit, inherited from base class

}

public override void Display()

{

base.Display();// Call Display, inherited from base class

Console.WriteLine("$5 charge if balance goes below ${0}", minBalance);

}

//You must override all abstract methods from the base class

public override double CalculateBankCharge()

{

if (balance < minBalance)

return 5.00;

else

return 0.00;

}

}

static void Main (string[] args)

{

//Account aca = new Account("sd", 1.1);//Cannot create an instance of the abstract class or interface

SavingsAccount sa = new SavingsAccount("Senthil", 100.00, 25);

sa.Display();

//call public methods in SavingsAccount or Account

sa.Credit(100);

sa.Debit(180);

sa.ChangeName("Kumar");

sa.Display();

Console.WriteLine("Bank charge: ${0}", sa.CalculateBankCharge());

}

Ref: http://support.microsoft.com/kb/307205