The BankAcount class has one attribute: the balance of the account. It will need two constructors, a default constructor to set the balance to zero, and a constructor to set the balance to the value passed. You will need methods to deposit an amount, withdraw an amount, get the balance of the account and transfer and amount from this account to another account.
The SavingsAccount class has one attribute: the interest rate. It will need one constructor that sets the interest rate. There should be one method that adds interest to the account.
The CheckingAccount class has attribute: a transaction counter. There also should be two constants: one fro the number of free transactions allowed, and another for the transaction fee. There is only one constructor that sets the initial balance (and it also should set the transaction counter.) There should be methods to deposit money into the account, withdraw money from the account, and a method to deduct fees from the account.
Both SavingsAccount and the CheckingAccount should inherit from the BankAccount class.
Download my test account AccountTest.java to make sure your classes work, then make a graphically interface to run the accounts.