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

Due on Tuesday, January 20 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, from ordering to final delivery, of the tasks that need to be performed in order to sending flowers to someone far away. 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:
First call the local florist and give them the necessary information. The florist record all the necessary data and find the appropriate remote florist. The local florist then transmits all the necessary data to the remote florist. The remote florist then records the data and then prepare the flowers for delivery. The remote florist must then locate the destination on a map, take the flowers to a delivery vehicle, and proceed to the destination. Upon arrival the flowers will be given to the recipient.
OO Paradigm:
In this paradigm 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.
Simple ATM Design Description
We should all be familiar with an ATM machine. 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.
The description is of a simple ATM without deposits and additional features.
Object Action break down
Object on the left takes action on Object on the right via a method call. Note: The Bank object does not talk to the ATM but responds to messages from the ATM. ATM might have a subobject called Card Reader.
Client - insert card - ATM/Card Reader
Client - enter pin - ATM/Key pad
ATM - check account - Bank
ATM - check funds - Bank
ATM - give money - client
Bank - debt. - Bank/account
ATM - receipt - Client
ATM - return card - Client
Question 3:
Use the ATM description to create a Module Diagram.

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

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

Bonus:
Stop! What is your name?
What is your quest?
What is your favorite color?
What is the air-speed velocity of an unladen swallow? Monty Python and the Holy Grail
End of Scene 23
KEEPER: Heh heh. Stop! What is your name?
ARTHUR: It is Arthur, King of the Britons.
KEEPER: What is your quest?
ARTHUR: To seek the Holy Grail.
KEEPER: What is the air-speed velocity of an unladen swallow?
ARTHUR: What do you mean? An African or European swallow?
KEEPER: What? I don't know that! Auuuuuuuugh!
BEDEVERE: How do know so much about swallows?
ARTHUR: Well, you have to know these things when you're a king you know.

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

Due on Tuesday, January 20 at the start of class.

Question 1:

Answer:

Question 2:

Answer:

Simple ATM Design Description

Object Action break down

Question 3:

Question 4:

Question 5:

Bonus:

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