Practice Quiz 6 Design Considerations (mostly refactorings)
C Sc 335 ANSWERS Design Refactoring, Coupling, Cohesion, Principles of.
1) b When a method name does not reveal its purpose, change the name of the method. Use the refactoring
“Rename Method” to change empty to isEmpty (unless empty does really empty the container). BTW: The
C++ STL has many collection classes (stack, queue, list) where empty does not mean empty, it returns true if
the stack isEmpty. Also, pop can modify and return as long as it is documented. You could argue that pop
should only modify, and some people do.
2) b Whenever there is a public field, make it private and provide accessors. This prevents other object from
modifying a field, which would be the worst form of coupling. Use the "Encapsulate Field" refactoring
(Eclipse has this refactoring)
3) a The while loop is difficult to read, trace, and understand. And it is longer. The recursive solution can be
easier to understand. Use the refactoring Replace iteration with Recursion to make more readable code.
BTW: Worried about all of those method calls at runtime? A compiler can make the code to the left run as fast
as the code to the right. And you should wait until you profile the code to see if this is a bottleneck
4) b When you have a complicated conditional (if-then-else) statement, use the refactoring "Decompose
Conditional". Extract methods from the Boolean condition
4B) Yes Apply "Rename Method" and have the method return the logical negation, then apply "Reverse
Conditional"
5) a Whenever a method returns an object that needs to be downcasted by its callers, use the "Encapsulate
Downcast" refactoring to move the downcast to within the method.
5b) Use generics so you do not have to cast whil providing type safety to avoid the wrong types from being
added to or returned fro a collection. With generics you get a compiletime error rather than a class cast
exception at runtime.
6) b The design on the left has one class doing work that should be done by two. Use the "Extract Class"
refactoring to create a new class and move the relevant fields and methods from the old class into the new class.
7) b If you have a code fragment that can be grouped together, use Extract Method to turn the fragment into a
method whose name explains the purpose of the method.
8) b When a method is not used by any other class, use the refactoring "Hide Method" to make the method
private. Why: Do not clutter the public interface with methods the user does not need or is not going to be
interested in.
9) b Magic numbers often don’t reveal their meaning very well (we usually know 3.14, but what is 0.045 (BTW
it is the VA state sales tax, I think) If you have a literal number with a particular meaning, create a constant,
name it after the meaning, and replace the number with it. Apply " Replace Magic Number with Symbolic
Constant".
10) b Class with low coupling reduce the risk of cascading changes when a change is made to one.
11) Neither Use whatever coding style your team, project or instructor demand
12) a Because the code uses two indirect objects to get the tail wagging
13) When a method send a message to one of its parameters
14) An instance variable (there are 4 possible answers to this question: other three: parameter of a method, an
object created by the method, or )
15) Rigidity: When one change requires many other changes
16) Strategy is Open-Closed Principle because implementing a new Strategy does not require a change
to the classes that depend upon it.
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