//BankAccount.java source code

/**
   A bank account has a balance that can be changed by 
   deposits and withdrawals.
*/
public class BankAccount
{ 
    
    
   /**
      Constructs a bank account with a zero balance.
   */
   public BankAccount()
   {   
      balance = 0;
   }

   /**
      Constructs a bank account with a given balance.
      @param initialBalance the initial balance
   */
   public BankAccount(double initialBalance)
   {   
      balance = initialBalance;
      numTransactions = 0;
   }

   /**
      Deposits money into the bank account.
      @param amount the amount to deposit
   */
   public void deposit(double amount) {  
      this.updateTransactionCount();
      double newBalance = balance + amount;
      balance = newBalance;
   }

   /**
      Withdraws money from the bank account.
      @param amount the amount to withdraw
   */
   public void withdraw(double amount) {  
      this.updateTransactionCount();
      
      double newBalance = balance - amount;
      if (newBalance < 0) {
          /* do nothing */
          System.err.println( "Denied!  balance is " + balance );
          }
      else {
          balance = newBalance;
          }
   }

   /**
      Gets the current balance of the bank account.
      @return the current balance
   */
   public double getBalance()
   {   
      return balance;
   }


   /** Update the transaction count by one,
    * charging a fee if necessary.
    */
   private void updateTransactionCount() {
       numTransactions = numTransactions + 1;

       if (numTransactions > FREE_TRANSACTIONS) {
          balance = balance - TRANSACTION_FEE;
          }
       }
   
   
   public static final int FREE_TRANSACTIONS = 4;
   public static final double TRANSACTION_FEE = 2.50;

   private double balance;
   private int numTransactions;
}