1. Faculty of Science
Department of Computing
Final Examination 2013
Unit: COMP229 Object Oriented Programming Practices
Release Date: 9:00am, November 15, 2013
Due Date: 11:45pm, November 19, 2013
Total Number
of Questions: Six (6)
Total Marks: Sixty Four (68)
Instructions: Answer ALL questions.
All references to program code or behaviour refer to the Java
language.
All answers to questions that ask for code must be written using
Java.
Every attempt has been made to make questions unambiguous.
However, if
you are not sure what a question is asking, make some
reasonable assumption
and state it at the beginning of your answer.
COMP229 Object Oriented Programming Practices, November

2. 2013
Question 1 (Design Patterns, 5 marks)
The template method pattern and the strategy pattern both
abstract some computation in
the form of methods. What defining characteristic distinguishes
the template method patern
from the strategy pattern? Explain your answer. [5 marks]
Question 2 (Concurrency, 12 marks)
Consider the following class definition. This class is considered
to be in an inconsistent state
if the isConsistent() method returns falsefalsefalse;
publicpublicpublic classclassclass Foo {
longlonglong mValue;
longlonglong mValueTimesTwo;
/**
* Sets the state of our object.
*
* Pauses briefly between setting the first and second
* values in order to increase the probability that the
* object will be interrogated while in an inconsistent
* state.

3. *
* @param pValue the value to update the current state with ,
*/
publicpublicpublic synchronizedsynchronizedsynchronized
voidvoidvoid setValues(longlonglong pValue) {
mValue = pValue;
doPause (3);
mValueTimesTwo = pValue * 2;
}
/**
* Checks to see if the current state of our object is
* consistent.
*
* @return true if it is.
*/
publicpublicpublic synchronizedsynchronizedsynchronized
booleanbooleanboolean isConsistent () {
returnreturnreturn (mValue * 2 == mValueTimesTwo );
}

4. /**
* Utility routine - pauses our thread by calling
* sleep and supressing any InterruptedException.
*/
privateprivateprivate staticstaticstatic voidvoidvoid
doPause(longlonglong pPause) {
trytrytry {
Thread.sleep(pPause );
} catchcatchcatch (InterruptedException e) {
e.printStackTrace ();
}
}
}
Page 1 of 5
COMP229 Object Oriented Programming Practices, November
2013
a. Imagine a hypothetical version of Java where the object lock
is replaced by a method
lock. Under this system a call to a synchronised method would
assign a lock for that

5. method to the calling thread. No other thread could then call
this method because
the lock is already allocated. However, other methods of the
same object could still
be called. Upon the method completing, the lock is released.
Under this system, is it
possible to put an instance of the Foo class into an inconsistant
state? If so, give a code
example which could create this situation and explain how it
does so. If not, explain
how the method lock prevents the possibility of inconsistent
state. [7 marks]
b. Provide one possible motivation for choosing this
hypothetical method lock over an
object lock. Explain your answer. [5 marks]
Question 3 (Generics, 15 marks)
Consider the following interface definition
/**
* This is an interface which abstracts the concept of a
* function. The interface has methods for a number of
* possible function call styles.
*
* @param <T> The type over which these functions work.
**/
publicpublicpublic interfaceinterfaceinterface Functions <T> {

6. /**
* A function which does not return a value
*
* @param in The parameter to this function
**/
publicpublicpublic abstractabstractabstract voidvoidvoid doIt(T
in);
/**
* A function which turns a T into an integer
*
* @param in The parameter to this function
**/
publicpublicpublic abstractabstractabstract intintint calculate(T
in);
/**
* A function which turns a T into an String
*
* @param in The parameter to this function
**/

7. publicpublicpublic abstractabstractabstract String show(T in);
/**
* A function which creates a T based on an integer
*
* @param in The parameter to this function
**/
publicpublicpublic abstractabstractabstract T generate(intintint
in);
/**
* This function , called "transform" returns a value of the same
type
* as the parameter it was given.
Page 2 of 5
COMP229 Object Oriented Programming Practices, November
2013
*
* @param in The parameter to this function
* @return A value of the same type as the input parameter

8. **/
// FIXME: Write this method signature
}
a. This interface is part of an implementation of a design
pattern. Which design pattern
is it from? Give the standard class diagram for the pattern and
identify which part of
the pattern is being implemented with the above interface. [6
marks]
b. How does this instance of the pattern differ from the standard
version? [2 marks]
c. The final method signature has been left out. Write what you
think that signature
should be. [7 marks]
Question 4 (Refactoring, 16 marks)
Consider the following class definition. It is not necessary that
you know anything about the
system from which this class was taken, nor is it necessary to
know anything about the classes
Expr, Number or Boolean.
publicpublicpublic classclassclass Infer <T> {
Expr <T> expr;
publicpublicpublic Infer(Expr <T> e){
expr = e;

9. }
/**
* @param inferenceType The type of inference to perform.
* 0 is simple inference , 1 is polymorphic inference ,
* 2 is explicit inference.
**/
publicpublicpublic booleanbooleanboolean doInference(intintint
inferenceType ){
ififif (inferenceType == 0)
ififif (expr.isVal ())
ififif (expr.isDefined ())
returnreturnreturn truetruetrue;
elseelseelse
returnreturnreturn falsefalsefalse;
elseelseelse ififif (expr.isPlus ()){
returnreturnreturn (newnewnew Infer <Number >(expr.left )).
doInference(inferenceType)
&& (newnewnew Infer <Number >(expr.right )).
doInference(inferenceType );
}

10. elseelseelse ififif (expr.isMinus ()){
returnreturnreturn (newnewnew Infer <Number >(expr.left )).
doInference(inferenceType)
&& (newnewnew Infer <Number >(expr.right )).
doInference(inferenceType );
}
elseelseelse ififif(expr.isAnd ()){
returnreturnreturn (newnewnew Infer <Boolean >(expr.left )).
doInference(inferenceType)
&& (newnewnew Infer <Boolean >(expr.right )).
doInference(inferenceType );
}
elseelseelse ififif(inferenceType == 1)
ififif (expr.isVal ())
Page 3 of 5
COMP229 Object Oriented Programming Practices, November
2013
ififif (expr.isDefined ())
returnreturnreturn falsefalsefalse;

11. elseelseelse
returnreturnreturn truetruetrue;
elseelseelse ififif (expr.isPlus ()){
returnreturnreturn (newnewnew Infer <Number >(expr.left )).
doInference(inferenceType)
&& (newnewnew Infer <Number >(expr.right )).
doInference(inferenceType );
}
elseelseelse ififif (expr.isMinus ()){
returnreturnreturn (newnewnew Infer <Number >(expr.left )).
doInference(inferenceType)
&& (newnewnew Infer <Number >(expr.right )).
doInference(inferenceType );
}
elseelseelse ififif(expr.isAnd ()){
returnreturnreturn (newnewnew Infer <Boolean >(expr.left )).
doInference(inferenceType)
&& (newnewnew Infer <Boolean >(expr.right )).
doInference(inferenceType );
}
elseelseelse

12. returnreturnreturn truetruetrue;
}
}
a. Identify as many code smells as you can in the above class.
Hint: There are at least
two. [6 marks]
b. Refactor the class to remove all the code smells you
identified. Give the full definition
of your refactored class and an explanation of the refactorings
you performed.
[10 marks]
Question 5 (Design Patterns, 8 marks)
(a) There is something wrong with the following instance of the
Template Method pattern.
Explain what is wrong. Modify the system so that it conforms to
the pattern. Explain
each of the changes you made to the system. Draw the class
diagram for your modified
system. [8 marks]
Page 4 of 5
COMP229 Object Oriented Programming Practices, November
2013
Question 6 (Testing, 12 marks)

13. (a) The following diagram shows the classes used in a
calculator application. This cal-
culator application can do addition, multiplication, powers,
logarithms, factorials and
permutations. Some of these calculations can take a long time
on the low-powered de-
vice on which it is designed to run. For this reason, the
calculator takes each calculation
it is asked to do and sends it over the internet to a
supercomputer for computation as
well as attempting to calculate it locally. If the supercomputer
returns the result faster
than the program can calculate it, it uses that result.
Furthermore, the computer on
which this application is running has a large amount of memory,
so the application will
store all the calculations it has already performed in a database.
If it is asked to do
a calculation it has done before, it uses the value it has stored in
the database. This
database can store 100,000 results before it is full and when it
is full the calculator will
have to do any new calculations every time they are requested.
At least the database class will need to be stubbed with mock
objects for testing be-
cause you need to test for empty, partially full, and completely
full databases. Which
other classes do you think will need to be stubbed with mock
objects for testing the
application? For each class you identify explain why you think
that class needs mocking
and at least three different mocked behaviours you will need.
[12 marks]

14. END OF EXAMINATION
Page 5 of 5
• 2- Topic Selection
Please post the topic you plan to explore. Include why you
selected it and how it impacts your profession.
Your submission should be at least 250 words after which you
must comment to at least two of your peers.
At the end of the discussion, you will be asked to craft a 150
word reflection on what you have learned through this
conversation and post it to the Weekly Reflection Journal. The
more active you are in this part of the discussion, the more you
will have to draw from in your reflection, so get involved, be
active, help out your classmates when they need it, and, most of
all, enjoy the conversation
• 3- Discipline Areas (Bodies of Knowledge)
The following topic(s) will demonstrate what the discussion is
about, but feel free to branch off or expand on the topics. At the
end of the discussion, you will be asked to craft a 150 word
reflection on what you have learned through this conversation
and post it to the Weekly Reflection Journal. The more active
you are in this part of the discussion, the more you will have to
draw from in your reflection, so get involved, be active, help
out your classmates when they need it, and, most of all, enjoy
the conversation.
Your research paper must address a profession-related issue
from at least two discipline perspectives. Please discuss the
following questions about your proposed project:
• How do the two areas you have selected relate to the
issue?
• How do they appear to overlap?
• What challenges have you encountered so far in
finding information relevant to your topic and how will you
address those challenges? After you have posted your

15. discussion, please comment to at least two of your peers.
•
• 4- Discoveries (So Far)
The following topic(s) will demonstrate what the discussion is
about, but feel free to branch off or expand on the topics. At the
end of the discussion, you will be asked to craft a 150 word
reflection on what you have learned through this conversation
and post it to the Weekly Reflection Journal. The more active
you are in this part of the discussion, the more you will have to
draw from in your reflection, so get involved, be active, help
out your classmates when they need it, and, most of all, enjoy
the conversation.
Using the mind mapping and article evaluations completed in
W3, discuss two things that surprised you regarding your topic.
Additionally, are you on track with your topic or have you
discovered that you may need to make some changes? Why or
why not? Please respond to at least two of your colleagues
• 5- Self-Evaluation of Your Paper
The following topic(s) will demonstrate what the discussion is
about, but feel free to branch off or expand on the topics. At the
end of the discussion, you will be asked to craft a 150 word
reflection on what you have learned through this conversation
and post it to the Weekly Reflection Journal. The more active
you are in this part of the discussion, the more you will have to
draw from in your reflection, so get involved, be active, help
out your classmates when they need it, and, most of all, enjoy
the conversation.
Using the checklist on p. 130 of the text, evaluate your first
draft. Discuss the strengths and weaknesses you found regarding
your own writing and how you plan to build upon and/or
improve what you discovered. Please respond (or give advice)
to at least two of your peers.
• 6- Enhancing the Paper
The following topic(s) will demonstrate what the discussion is
about, but feel free to branch off or expand on the topics. At the

16. end of the discussion, you will be asked to craft a 150 word
reflection on what you have learned through this conversation
and post it to the Weekly Reflection Journal. The more active
you are in this part of the discussion, the more you will have to
draw from in your reflection, so get involved, be active, help
out your classmates when they need it, and, most of all, enjoy
the conversation.
Having written the first draft of your paper (and using the
article review worksheet completed in W3), please discuss the
following issues related to your topic:
• What are some potential ethical issues that must be
considered?
• How might this issue impact different communities
from diverse perspectives? (For example, are there differences
based on age, gender, economics, political, ethnic, religious,
educational or geographic?) Please respond to at least two of
your peers.
•
• 7- Using My Research
The following topic(s) will demonstrate what the discussion is
about, but feel free to branch off or expand on the topics. At the
end of the discussion, you will be asked to craft a 150 word
reflection on what you have learned through this conversation
and post it to the Weekly Reflection Journal. The more active
you are in this part of the discussion, the more you will have to
draw from in your reflection, so get involved, be active, help
out your classmates when they need it, and, most of all, enjoy
the conversation.
Discuss how (or if) what you have discovered has (or will)
change your role within the communities in which you are a
member. Why or why not? Please respond to at least two of
your colleagues.
• 8- Abstract of Paper
The following topic(s) will demonstrate what the discussion is

17. about, but feel free to branch off or expand on the topics. At the
end of the discussion, you will be asked to craft a 150 word
reflection on what you have learned through this conversation
and post it to the Weekly Reflection Journal. The more active
you are in this part of the discussion, the more you will have to
draw from in your reflection, so get involved, be active, help
out your classmates when they need it, and, most of all, enjoy
the conversation.
Please summarize the findings of your paper and discuss how
you will use what you have discovered in your profession and in
the future.