CS 4448 - Fall 1998
Object-Oriented Programming and Design
Homework #1 - A Solution

Due on Monday, August 31 at the start of class.

Question 1:

Smalltalk says there is one root in the inheritance hierarchy while C++ does not. What are the pros and cons of these two strategies? What types of designs and frameworks do you think would require C++ to enforce a single root in the inheritance hierarchy?
Answer:
One definite pro of a one rooted object inheritance model is the default functionality that can be automatically incorporated into all objects. In this way all objects can be required to have various functionality such as displaying themselves and basic messages about state. From the programming side one can simply assume that all objects have this basic functionality through completely standardized methods. Another good aspect of a one rooted model is the flexibility to deal with many objects of varying types without even knowing of what type they are. For example this is a very powerful feature of Java, because every instance of a class is at least an Object and there are no problems with being ambiguous toward typing. However for that assumed functionality there is also a cost in that all objects must be homogeneous in their basic behavior. So an obvious pro of a multiple rooted model is the ability to work with fundamentally heterogeneous objects. New objects can be created that don't need the baggage that must be inherited in a singly rooted model. I think a single rooted object model should be enforced in cases where doing a basic task requires many objects to communicate given only a very simple interface.
An example would be a design in which many different advisors or managers stemming from different intermediate hierarchies would need to communicate and weigh out their decisions with only minimal knowledge of the sources of the decisions made by each other. In C++, ET++ and other frameworks require all objects have some basic functionality. ET++ is a large graphical package which can be used in C++. Using ET++, a programmer can quickly build a program with many fancy graphics. It is required that all objects have type information, like in Smalltalk, and be derived from the same base class. In this way the draw_yourself method can be called on any object and it works. Also, one object can question another object as to its type and then decide how to deal with the other object.
Question 2:
In English give a detailed description of how a user interacts with an ATM machine in order to make a withdrawal. Start with the client approaching the ATM machine and finish with the client leaving with some money. You should include the user(keypads, bank card, etc.), the local(ATM machine) and remote(Bank Computer) hardware. In the first paragraph describe the process using an imperative(procedural) paradigm. In the second paragraph use an object oriented paradigm which should involve methods(messages) and objects(agents).

Answer:
Imperative Paradigm:
A client approaches the ATM and inserts the card into the ATM-Card reader. The client then enters a pin number on the keypad. The pin number and account number is then checked with the bank. If the information is valid then the client can and will request some funds. The ATM checks with the bank to see if the funds are available. If they are available then the client is given the money, the account balance reflects the transaction, and a receipt is printed for the clients records. The client is then returned the card. This one should have much more detail....
OO Paradigm:
There are a bunch of objects including: User, ATM, Bank, and Account. The ATM contains the Printer, Card Reader, Screen, Keypad, and Money Dispenser Objects. The User approaches the ATM. The ATM has already told its Screen to informs the User to talk to the Card Reader. The ATM has also told the Card Reader to get information from the User. The User tells the Card Reader its account information. The Card Reader then returns that information to the ATM. The ATM then tell the Screen to tell the User to enter a PIN number and dollar amount requested. The ATM also tells the Keypad to get the information. The Keypad returns the PIN number and requested dollar amount. The ATM now contacts the Bank asking for cash and passing the account information. The Bank then asks the Account if the information is correct and the funds are available. The Account then checks the information and returns yes or no. The Bank then tells the ATM that it is okay. The ATM then tell the Money Dispenser to give the money. The Money Dispenser returns okay if it is successful. The ATM then tells the bank that the money was given. The Bank tell the Account that the transaction has occured. etc.....
Simple Flower Delivery Design Description
We have a sender, local and remote florists, and recipient. The sender will send a message to the local florist requesting flowers be sent to a recipient. The local florist then turns around and sends a message to the remote florist with the same request. The remote florist may then locate the recipient using a locate object with a find method. The remote florist then delivers the flowers to the recipient.
Question 3:
Use the Flower Delivery description to create a Module Diagram.

Question 4:
Use the Flower Delivery description to create a State Transition Diagram.

Question 5:
Use the Flower Delivery description to create an Interaction Diagram.

CS 4448 - Fall 1998 Object-Oriented Programming and Design Homework #1 - A Solution

Due on Monday, August 31 at the start of class.

Question 1:

Answer:

Question 2:

Answer:

Simple Flower Delivery Design Description

Question 3:

Question 4:

Question 5:

CS 4448 - Fall 1998
Object-Oriented Programming and Design
Homework #1 - A Solution