The Updated BankAccount Class in C#.NET

Make Code39 in C#.NET The Updated BankAccount Class

The program ConstructorSavingsAccount, found on the Web site, is an updated version of the SimpleBankAccount program In this version, however, the SavingsAccount constructor can pass information back to the BankAccount constructors Only Main() and the constructors themselves are shown here:

// ConstructorSavingsAccount -- Implement a SavingsAccount as // a form of BankAccount; use no virtual methods, but // implement the constructors properly using System; namespace ConstructorSavingsAccount { // BankAccount -- Simulate a bank account, each of which carries an // account ID (which is assigned upon creation) and a balance public class BankAccount { // Bank accounts start at 1000 and increase sequentially public static int _nextAccountNumber = 1000; // Maintain the account number and balance for each object public int _accountNumber; public decimal _balance; // Constructors public BankAccount() : this(0) { } public BankAccount(decimal initialBalance) {

_accountNumber = ++_nextAccountNumber; _balance = initialBalance; } public decimal Balance { get { return _balance; } // Protected setter lets subclass use Balance property to set protected set { _balance = value; } } // Deposit -- Any positive deposit is allowed public void Deposit(decimal amount) { if (amount > 0) { Balance += amount; } } // Withdraw -- You can withdraw any amount up to the // balance; return the amount withdrawn public decimal Withdraw(decimal withdrawal) { if (Balance <= withdrawal) { withdrawal = Balance; } Balance -= withdrawal; return withdrawal; } // ToString -- Stringify the account public string ToBankAccountString() { return StringFormat( {0} - {1:C} , _accountNumber, Balance); } } // SavingsAccount -- A bank account that draws interest public class SavingsAccount : BankAccount { public decimal _interestRate; // InitSavingsAccount -- Input the rate expressed as a // rate between 0 and 100 public SavingsAccount(decimal interestRate) : this(interestRate, 0) { } public SavingsAccount(decimal interestRate, decimal initial) : base(initial) { this_interestRate = interestRate / 100; } // AccumulateInterest -- Invoke once per period public void AccumulateInterest() { // Use protected setter and public getter via Balance property Balance = Balance + (decimal)(Balance * _interestRate); } // ToString -- Stringify the account public string ToSavingsAccountString() { return StringFormat( {0} ({1}%) , ToBankAccountString(), interestRate * 100); } } public class Program { // DirectDeposit -- Deposit my paycheck automatically

public static void DirectDeposit(BankAccount ba, decimal pay) { baDeposit(pay); } public static void Main(string[] args) { // Create a bank account and display it BankAccount ba = new BankAccount(100M); DirectDeposit(ba, 100M); ConsoleWriteLine( Account {0} , baToBankAccountString()); // Now a savings account SavingsAccount sa = new SavingsAccount(125M); DirectDeposit(sa, 100M); saAccumulateInterest(); ConsoleWriteLine( Account {0} , saToSavingsAccountString()); // Wait for user to acknowledge the results ConsoleWriteLine( Press Enter to terminate ); ConsoleRead(); } } }

BankAccount defines two constructors: one that accepts an initial account balance and the default constructor, which does not To avoid duplicating code within the constructor, the default constructor invokes the BankAccount(initial balance) constructor using the this keyword The SavingsAccount class also provides two constructors The SavingsAccount(interest rate) constructor invokes the SavingsAccount(interest rate, initial balance) constructor, passing an initial balance of 0 This most general constructor passes the initial balance to the BankAccount(initial balance) constructor using the base keyword, as shown in Figure 6-1

Bank Account (0) passes balance to base class Savings Account (125%), 0) defaults balance to 0 Savings Account (125%)

C# provides a method that s inverse to the constructor: the destructor It carries the name of the class with a tilde (~) in front For example, the ~BaseClass() method is the destructor for BaseClass C# invokes the destructor when it is no longer using the object The default destructor is the only destructor that can be created because the destructor cannot be invoked directly In addition, the destructor is always virtual When an inheritance ladder of classes is involved, destructors are invoked in reverse order of constructors That is, the destructor for the subclass is invoked before the destructor for the base class The destructor method in C# is much less useful than it is in other object-oriented languages, such as C++, because C# has nondeterministic destruction Understanding what that term means and why it s important requires some explanation The memory for an object is borrowed from the heap when the program executes the new command, as in new SubClass() This block of memory remains reserved as long as any valid references to that memory are used by any running programs You may have several variables that reference the same object The memory is said to be unreachable when the last reference goes out of scope In other words, no one can access that block of memory after no more references to it exist C# doesn t do anything in particular when a memory block first becomes unreachable A low-priority system task executes in the background, looking for unreachable memory blocks To avoid negatively affecting program performance, this garbage collector executes when little is happening in your program As the garbage collector finds unreachable memory blocks, it returns them to the heap Normally, the garbage collector operates silently in the background The garbage collector takes over control of the program for only a short period when heap memory begins to run out The C# destructor for example, ~BaseClass() is nondeterministic because it isn t invoked until the object is garbage-collected, and that task can occur long after the object is no longer being used In fact, if the program terminates before the object is found and returned to the heap, the destructor is never invoked Nondeterministic means you can t predict when the object will be garbage-collected It could be quite a while before the object is garbage-collected and its destructor called C# programmers seldom use the destructor C# has other ways to return borrowed system resources when they re no longer needed, using a Dispose() method, a topic that s beyond the scope of this book (You can search for the term Dispose method in Help)