//An instance of this class represents a basic bank account that permits
// the usual transactions with any non-negative transaction amount: 
//       deposit(), withdraw(), transfer()
//
public class BankAccount
{
   //Instance (State) Variables
   private String accountNumber; //Account Number
   private double currentBalance;//Current Balance
      
   //Parameterized Constructor: 
   // Create a new BankAccount with a given initial balance
   // and a unique (automatically generated) account number
   public BankAccount(double initialBalance)
   {
      this.accountNumber = newAccountNumber();
      this.credit(initialBalance);
   }
   
   //Parameterless Constructor: 
   // Create a new BankAccount with 0.0 initial balance
   public BankAccount()
   {
      this(0.0);
   }
   
   //Accessor: 
   // Return the account number of this BankAccount
   public String getAccountNumber()
   {
      return this.accountNumber;
   }
   
   //Accessor: 
   // Returns the current balance of this BankAccount
   public double getCurrentBalance()
   {
      return this.currentBalance;
   }
   
   //Mutator:
   // Add a given amount to the current balance of this BankAccount
   public void deposit(double amount)
   {
      this.credit(amount);
   }
   
   //Mutator:
   // Reduce the current balance of this BankAccount by a given amount
   public void withdraw(double amount)
   {
      if (amount > this.currentBalance)
         throw new RuntimeException("Insufficient Funds");
      this.debit(amount);
   }
   
   //Mutator:
   // Transfer a given amount to this BankAccount from another BankAccount
   public void transfer(double amount, BankAccount source)
   {
      source.withdraw(amount);
      this.deposit(amount);
   }
   
   //Override:
   // Return a printable image of the state of this BankAccount
   public String toString()
   {
      return this.getClass().getSimpleName() + " #" + this.accountNumber + 
                                               " Balance: $" + this.currentBalance;
   }

   //Override:
   // Return true iff this BankAccount is identical to another BankAccount
   public boolean equals(Object other)
   {
      if ( other == null )
         return false;
         
      if ( this.getClass() != other.getClass() )
         return false;
         
      BankAccount that = (BankAccount)other;
      return this.accountNumber.equals(that.accountNumber) &&
             this.currentBalance == that.currentBalance;
   }
   
   // Return an exact replica of this BankAccount
   // **** Will override inherited clone() method later ****
   public BankAccount copy()
   {
      BankAccount twin = new BankAccount(this.currentBalance);
      twin.accountNumber = this.accountNumber;
      
      this.seedNumber--;
      
      return twin;
   }
/*   
   //Override:
   // Return a copy of this BankAccount
   public Object clone()
   {
      try
      {
         return super.clone();
      }
      catch (CloneNotSupportedException cnse)
      {
         throw new RuntimeException("Clone: " + cnse.getMessage());
      }
   }
*/   
   //*********************************************************************
   //*********************************************************************
   //Class Variables and Methods      
   private static int seedNumber = 7000000;  //Base account accountNumber
   
   //Constructor Helper: 
   // Return a new unique account #
   private static String newAccountNumber()
   {
      seedNumber = seedNumber + 1;
      String accountNumber = "" + seedNumber;
      return accountNumber.substring(0, 1) + "-" +
             accountNumber.substring(1, 4) + "-" +
             accountNumber.substring(4);
   }
   
   //Helper:
   // Increase the balance of this BankAccount by a given amount
   private void credit(double amount)
   {
      validate(amount);
      this.currentBalance += amount;
   }
   
   //Helper:
   // Decrease the balance of this BankAccount by a given amount        
   private void debit(double amount)
   {
      validate(amount);
      this.currentBalance -= amount;
   }
   
   //Helper:  
   // Validate the amount of any BankAccount creation or transaction
   // Throw a RuntimeException if the amount is negative (< 0.0)
   private static void validate(double amount)
   {
      if (amount < 0.0)
         throw new RuntimeException("Invalid amount $" + amount);
   }      
}