CUSTOMER_CODE
SMUDE
DIVISION_CODE
SMUDE
EVENT_CODE
JAN2016
ASSESSMENT_CODE BT9303_JAN2016
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
36862
QUESTION_TEXT
Explain the benefits of prototype patterns.
Benefits: (5×2=10 marks)
●
Adding and removing of the prototype at tun time
●
Specifying new objects by varying values
●
Specifying new objects by varying structure
●
Reduced subclassing
●
Configuring an application with classes dynamically
SCHEME OF EVALUATION
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
36863
QUESTION_TEXT
Explain the applicability, advantages of façade pattern and who are its
participants.
SCHEME OF
EVALUATION
Applicability: (3×2=6 marks)
● A façade can provide a simple default view of the subsystem that is
good enough for clients.
● A façade decouples the subsystem from clients and other subsystems,
promoting subsystem independence and portability
● Use a façade to define an entry point to each subsystem level.
Participants: (1 mark)
● Facade
● subsystem classes
Advantages: (3 marks)
● It shields clients form subsystem components.
● It promotes weak coupling between the subsystem and its clients.
● It doesn’t prevent applications from using subsystem classes if they
need to.
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
36864
QUESTION_TEXT
Explain the benefits and drawbacks of mediator pattern.
SCHEME OF EVALUATION
● It limits subclassing
● It decouples colleagues
● It simplifies object protocols
● It abstracts how objects cooperate
● It centralizes control
(2 marks each)
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
125950
QUESTION_TEXT
What is iterator pattern? Explain its applicability and its consequences.
Iterator pattern provides a way to access the elements of an aggregate object
sequentially without exposing its underlying representation. It is also known as
‘cursor’. (2 marks)
Applicability: (3 marks)
SCHEME OF
EVALUATION
Use the Iterator pattern
to access an aggregate object's contents without exposing its internal
representation.
to support multiple traversals of aggregate objects.
•
to provide a uniform interface for traversing different aggregate structures
(that is, to support polymorphic iteration).
Consequences: (6 marks)
The Iterator pattern has three important consequences:
1. It supports variations in the traversal of an aggregate. Many ways
can traversed by compelx aggregates. For example, code generation and
sematic checking may traverse the parse trees. The pre order or in order
may be used in code generator. Traversal algorithm can be made eassy
under iterators. It is just by replacing iterator with different one. New
traversal can be defined by iterator subclasses.
2. Iterators simplify the Aggregate interface. The need is obviates the
interface in Aggregate by iterator’s traversal interface. So that simplified
aggregates interface is available.
3.
More than one traversal can be pending on an aggregate. The each state
of iterator will be kept as a track of its own traversal state. So that user will
get more than one traversal in with one progress.
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
125951
QUESTION_TEXT
Explain the consequences of memento pattern.
SCHEME OF
EVALUATION
The Memento pattern has several consequences:
1. Preserving encapsulation boundaries. The confidential information are
known only to originator and memento always avoids for exposing. The
pattern protects other objects from originaotrs internals, so that preserves
the encapsulation of boundaries.
2. It simplifies Originator. The encapsulations are kept as backup which is
nothing but designs, so that various versions are available from internal
sates so that whenever client requested these need to be provided. These
back up keeping is one big burden, which is putted on originator.
Whenever the client asks for simplification then originator notifies when it
happens.
3. Using mementos might be expensive. Mementos are overloaded if lage
aount of information’s are stored or if client creates and returns the
mementos to originator is also possible. If encapsulation and restoring the
originator state is easy and less costing then the pattern may not be
appropriate.
4. Defining narrow and wide interfaces. In some languages ensure about
access of memento’s from originator.
5. Hidden costs in caring for mementos. If cares are taken by mementos then
caretaker is having the rights for deletion. But caretaker does not have any
information about how many number of states are existing in memento. Or
caretaker also can store large information with large storage devices which
stores all the memento’s.
(2 marks each)
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
125953
QUESTION_TEXT
What do you mean by a Design Pattern? Explain the four essential elements of
a Design Pattern.
i.
SCHEME OF
EVALUATION
ii.
Definition: Each design pattern describes a problem which occurs over
and over again in our environment, and then describes the core of the
solution to that problem, in such a way that you can use this solution a
million times over, without ever doing it the same way twice. In general a
pattern has four essential elements 2 marks
Pattern Name: it is a handle we can use to describe a design problem, its
solutions, and consequences in a word or two. It lets us design at a higher
level of abstraction. It makes it easier to think about designs and to
communicate them and their trade-offs to others. Finding good names has
been one of the hardest parts of developing our catalog 2 marks
iii.
iv.
v.
Problem: The problem describes when to apply the pattern. It explains
the problem and its context. It might describe specific design problems
such as how to represent algorithms as objects. It might describe class or
object structures that are symptomatic of an inflexible design. Sometimes
the problem will include a list of conditions that must be met before it
makes sense to apply the pattern 2 marks
Solution: The solution describes the elements that make up the design,
their relationships, responsibilities, and collaborations. The solution
doesn’t describe a particular concrete design or implementation, because
a pattern is like a template that can be applied in many different
situations. Instead, the pattern provides an abstract description of a
design problem and how a general arrangement of elements solves it. 2
marks
Consequences: The consequences are the result and trade-offs of
applying the pattern. Though consequences are often unvoiced when we
describe design decisions, they are critical for evaluating design
alternatives and for understanding the costs and benefits of applying the
pattern. The consequences for software often concern space and time
trade-offs. They may address language and implementation issues as
well. 2 marks