Microsoft 9GD00001 manual Microsoft Visual Studio 2010 a Beginner’s Guide

104Microsoft Visual Studio 2010: A Beginner’s Guide

GetCheckingAccounts, which I did on purpose so that you’ll see different ways to use loops; but this doesn’t affect the calling code because it’s encapsulated in individual methods. The point to make here is that GetCheckingAccounts will only return Checking class instances and GetSavingsAccounts will only return Saving class instances. The rest of the algorithm in the ProcessPayrollForCheckingAndSavingAccounts method mirrors the processing for Checking.

What should catch your attention is the duplication of code in the ProcessPayroll ForCheckingAndSavingAccounts method. Although the Credit methods of Checking and Saving should have different implementations, the code calling Credit can be the same, eliminating duplication. Listing 4-6 shows how to take advantage of the fact that both Checking and Saving implement the same interface, IAccount. You’ll see how to call Credit on any IAccount-derived type with one algorithm, eliminating the duplication you saw in Listing 4-5.

Listing 4-6 Processing payroll through the IAccount interface

C#:

public void ProcessPayrollForAllAccounts()

{

IAccount[] accounts = GetAllAccounts();

foreach (var account in accounts)

{

account.Credit(1000);

}

}

public IAccount[] GetAllAccounts()

{

IAccount[] allAccounts = new IAccount[4];

allAccounts[0] = new Checking(); allAccounts[1] = new Saving(); allAccounts[2] = new Checking(); allAccounts[3] = new Saving();

return allAccounts;

}