2.8.9. Account management: overdraft protection

A convenient feature of some bank accounts is overdraft protection; rather than bouncing a check when the balance would go negative, the bank would deduct the necessary funds from a second account. One might imagine such a setup for a student account, provided the student's parents are willing to cover any overdrafts (!). Another use is to have a checking account that is tied to a saving account, where the savings account covers overdrafts on the checking account.

Implement and test overdraft protection for Account objects, by completing the following steps.

1. Add a parentAccount instance variable to the Account class; this is the account that will provide the overdraft protection, and it may have overdraft protection of its own.
2. Add a two-argument constructor. The first argument will be the initial balance as in the existing code. The second argument will be an Account reference with which to initialize the instance variable you defined in step 1.
3. In the one-argument constructor, set the parent account to null.
4. Modify the withdraw method so that, if the requested withdrawal can't be covered by this account, the difference is withdrawn from the parent account. This may trigger overdraft protection for the parent account, and then its parent, and so onl you are not allowed to assume a limit on the number of accounts connected in this way. If the account doesn't have a parent and it can't cover the withdrawal, the withdraw method should merely print an error message as before and not change any account balances. Here's an example of the desired behavior, with the Account object kathy providing overdraft protection for the Account object megan.

   kathy balance	megan balance	attempted withdrawal from megan	desired result
   500	100	50	megan has 50, kathy has 500
   500	100	200	megan has 0, kathy has 400
   500	100	700	return false without changing either balance

   Don't use a loop to implement this feature.

5. Add tests to AccountTester.java sufficient to exercise all cases in the modified withdraw method.
6. Copy the updated Account.java and AccountTester.java (including the merge method) to a directory named day2. From within that directory, give the command submit day2. All we want in the day2 directory are .java files.