• deposit a certain amount into an account

• withdraw a certain amount from an account

• get the balance (i.e., the current amount) in an account

• transfer an amount from one account to another

The amount in the transactions is a value of type double. The accounts are identified by instances of the class Account that is in the package com.megabankcorp.records. The database class should be placed in a package called com.megabankcorp.system.

The deposit, withdraw, and balance operations should not have any implementation, but allow subclasses to provide the implementation. The transfer operation should use the deposit and withdraw operations to implement the transfer. It should not be possible to alter this operation in any subclass, and only classes within the package com.megabankcorp.system should be allowed to use this operation. The deposit and withdraw operations should be accessible in all packages. The balance operation should only be accessible in subclasses and classes within the package com.megabankcorp.system.