C# 4 and .NET 4

102 ❘ ChaPTer 4 inheritAnce
Notice the name of the interface, IBankAccount . It ’ s a convention that an interface name traditionally starts
with the letter I, so that you know it ’ s an interface.
Chapter 2, “ Core C#, ” pointed out that, in most cases, .NET usage guidelines
discourage the so - called Hungarian notation in which names are preceded by a letter
that indicates the type of object being defi ned. Interfaces are one of the few exceptions
in which Hungarian notation is recommended.
The idea is that you can now write classes that represent bank accounts. These classes don ’ t have to be
related to each other in any way; they can be completely different classes. They will, however, all declare
that they represent bank accounts by the mere fact that they implement the IBankAccount interface.
Let ’ s start off with the fi rst class, a saver account run by the Royal Bank of Venus:
namespace Wrox.ProCSharp.VenusBank
{
public class SaverAccount: IBankAccount
{
private decimal balance;
public void PayIn(decimal amount)
{
balance += amount;
}
public bool Withdraw(decimal amount)
{
if (balance > = amount)
{
balance -= amount;
return true;
}
Console.WriteLine("Withdrawal attempt failed.");
return false;
}
public decimal Balance
{
get
{
return balance;
}
}
public override string ToString()
{
return String.Format("Venus Bank Saver: Balance = {0,6:C}", balance);
}
}
}
code snippet BankAccounts.cs
It should be pretty obvious what the implementation of this class does. You maintain a private fi eld,
balance , and adjust this amount when money is deposited or withdrawn. You display an error message if
an attempt to withdraw money fails because there is insuffi cient money in the account. Notice also that,
because you want to keep the code as simple as possible, you are not implementing extra properties, such as
the account holder ’ s name! In real life that would be pretty essential information, but for this example it ’ s
unnecessarily complicated.
The only really interesting line in this code is the class declaration:
public class SaverAccount: IBankAccount
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