/**
   A bank account has a balance that can be changed by 
   deposits and withdrawals.
*/
public class BankAccount
{  
   // instance var
   private double balance ;
   
   /**
      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) 
   {  
      balance = balance + amount;
   }

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

   /**
      Gets the current balance of the bank account.
      @return the current balance
   */
   public double getBalance()
   {  
      return balance; 
   }
   
   /**
      Transfers money from the bank account to another account
      @param other the other account
      @param amount the amount to transfer
   */
   public void transfer(BankAccount other, double amount)
   {  
      withdraw(amount);
      other.deposit(amount);
   }
}