2007 Exam answers

Revision as of 04:08, 6 October 2008

Question 1

[26 marks for whole question] For each part (a)-(m), name the idea (or ideas) that best match the description and briefly explain your answer. If possible, include WikiNames.

1. (a) [2 marks] Keep the number of fields in a class small.

   Answer: One key abstraction, Large class smell, Single responsibility principle, Keep it simple, limit compositions in a class

2. (b) [2 marks] Methods should use most of the fields of the method’s object.

   Answer: Single responsibility principle, One key abstraction, Methods should use most fields of a class

3. (c) [2 marks] When several methods cooperate to do a job, give them the same name.

   Answer: Recursion introduction

4. (d) [2 marks] Objects should invoke methods of contained objects.

   Answer: Tell, don't ask, Beware accessors, Favor composition over inheritance

5. (e) [2 marks] A CodeSmell that supports one of RielsHeuristics.

   Answer: Switch statement smell Beware type switches Large class smell, supports minimize interface size

6. (f) [2 marks] A pattern that conflicts with TellDontAsk.

   Answer: Observer

7. (g) [2 marks] A pattern that supports TellDontAsk.

   Answer: Factory Method

8. (h) [2 marks] A pattern that employs DoubleDispatch.

   Answer: Visitor

9. (i) [2 marks] A pattern based on ModelTheRealWorld.

   Answer: Composite, Model view controller

10. (j) [2 marks] A pattern that conflicts with one of RielsHeuristics.

    Answer: Avoid no-op overrides, Composite

11. (k) [2 marks] A pattern that exhibits a CodeSmell.

    Answer: Iterator, Parallel inheritance hierarchies smell

12. (l) [2 marks] An architectural pattern that contains a design pattern.

    Answer: Observer + Strategy = Model view controller

13. (m) [2 marks] A design problem that the Waterfall Process was intended to fix.

    Answer: Big ball of mud

Question 2

[10 marks] Which of RielsHeuristics can be traced back to ideas described in JohnsonAndFoote1988? For each heuristic you identify, explain how it is based on the earlier idea.

Answer:

Question 3

[16 marks for whole question] For each of the following maxims (a)-(d) name other maxims (as many as you can) that support it. Briefly explain each answer.

1. [4 marks] ProgramToTheInterfaceNotTheImplementation.

   Answer:

2. [4 marks] SeparationOfConcerns.

   Answer:

3. [4 marks] SoftwareReuse

   Answer:

4. [4 marks] OpenClosedPrinciple

   Answer:

Question 4

[8 marks for whole question] Describe a design flaw in a 427 project produced by one of your classmates. Choose the most serious flaw you can find, clearly describe where it occurs (including where it can be found in the wiki) and support your argument, where possible, with maxims etc.

Answer:

Question 5

[5 marks] Imagine it was your job to interview an applicant for an OO design job. If you were allowed to ask only one question, and from the answer you had to judge whether the person was a skilled OO designer, what would you ask? Explain your reasoning.

Answer:

Question 6

[35 marks for whole question] See Trains design.