ch03/account/BankAccount.java
 /**
 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;
 }

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

 /**
 Withdraws money from the bank account.
 @param amount the amount to withdraw
 */
 public void withdraw(double amount)
 {
 double newBalance = balance - amount;
 balance = newBalance;
 }

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

 private double balance;
 }