Design Patterns

This quiz covers the concept of design patterns, their origin, the four essential elements of a pattern description, the Observer pattern in detail, other common patterns (Façade, Iterator, Decorator), and the role of patterns in supporting concept-level reuse in object-oriented software design

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QUESTION OF

Views #: 17

Questions #: 11

Time: 9 minutes

Pass Score: 80.0%

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Origin of Design Patterns

1 pts

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Design patterns were derived from ideas originally put forward by Christopher Alexander. What was the key insight from Alexander's work that was applied to software design?

That there are certain common patterns of design that are inherently effective and pleasing - a pattern is a description of the problem and the essence of its solution, so the solution may be reused in different settings

That all software can be described using exactly 23 patterns and nothing else

That software design should always be done graphically, never in text

That patterns eliminate the need for any software testing

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The Gang of Four

1 pts

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The most influential set of design patterns was published in 1995. Which of the following correctly describes this publication and its significance?

A journal article by Bass, Clements, and Kazman on architectural patterns

A book by Booch et al. defining the UML notation for object-oriented modeling

A book by Gamma, Helm, Johnson, and Vlissides ('Gang of Four') describing 23 general-purpose object-oriented design patterns that have become a vocabulary for talking about software design

A government standard mandating the use of patterns in safety-critical systems

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Four Essential Elements of a Design Pattern

1 pts

The Gang of Four defined four essential elements that every design pattern description should include. Match each element to its correct description.

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Element

Name

Solution description

Problem description

Consequences

Description

A meaningful reference to the pattern - patterns become part of the vocabulary for discussing designs

Explains when the pattern may be applied, including motivation (why it is useful) and applicability (situations where it may be used)

A template for the design solution that can be instantiated in different ways; describes the parts, their relationships and responsibilities; often expressed graphically showing object relationships

A statement of the results and trade-offs of applying the pattern; helps designers understand whether the pattern can be used in a particular situation

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Observer Pattern - Description

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The Observer pattern is one of the most widely used design patterns. Which of the following correctly describes what problem it solves and how?

It provides a single unified interface to a set of interfaces in a subsystem, reducing coupling between subsystems

It provides a standard way to traverse a collection of objects without exposing the underlying collection implementation

It allows functionality to be added to an individual object at runtime without affecting other objects

It separates the display of the state of an object from the object itself, allowing alternative displays; when the object state changes, all displays are automatically notified and updated

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Observer Pattern - Four Objects

1 pts

The Observer pattern involves two abstract objects and two concrete objects. Match each object to its role.

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Object

Observer

Subject

ConcreteObserver

ConcreteSubject

Role

Abstract object that maintains state and provides Attach, Detach, and Notify operations; does not know details of the concrete class

Abstract object that defines the Update() interface that all observers must implement

Inherits from Subject; maintains subjectState and provides GetState(); notifies observers when state changes

Inherits from Observer; maintains a copy of subjectState and implements Update() to keep its copy in step with the subject

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Observer Pattern - Consequences

1 pts

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Which of the following correctly describes a consequence (trade-off) of using the Observer pattern?

Using the Observer pattern eliminates the need for a separate Model component in MVC

The Observer pattern guarantees that all observer updates are processed in a fixed, deterministic order

The subject knows the full details of all concrete observer classes, creating tight coupling

The subject only knows the abstract Observer interface, creating minimal coupling; however, optimizations that enhance display performance are impractical, and changes to the subject may cause a set of linked updates to observers, some of which may be unnecessary

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Four Common Design Pattern Problems

1 pts

The Gang of Four documented problems that commonly arise in OO design. Match each problem to the pattern that solves it.

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Problem

Tell several objects that the state of some other object has changed

Tidy up the interfaces to a number of related objects that have often been developed incrementally

Provide a standard way of accessing the elements in a collection, irrespective of how that collection is implemented

Allow for the possibility of extending the functionality of an existing class at runtime

Pattern

Decorator

Façade

Observer

Iterator

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Patterns vs Component Reuse

1 pts

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Design patterns support 'concept-level reuse' rather than 'component reuse'. What is the key advantage of concept-level reuse through patterns compared to reusing executable components?

Patterns are always faster to implement than using library components

Pattern reuse means you never need to write any new code

With patterns you reuse the ideas and adapt the implementation to suit your system, avoiding the constraints imposed by a component's specific algorithms, object types, and interfaces that might conflict with your requirements

Patterns eliminate the need to understand algorithms used in the implementation

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Using Patterns in Practice

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Which of the following statements about using design patterns in practice are TRUE? Select ALL that apply.

Patterns have become a vocabulary for talking about software design - you can explain your design by describing the patterns you have used

When you start designing a system, it can be difficult to know in advance if you will need a particular pattern; pattern use often involves developing a design, experiencing a problem, and then recognizing that a pattern can be applied

Patterns are most effective when the designer can focus on the 23 general-purpose patterns from the Gang of Four's original book

If your problem is different from those addressed by the well-known patterns, you may find it difficult to find an appropriate pattern among the hundreds that have been proposed

Inexperienced programmers, even if they have read the pattern books, will always find it easy to decide when to reuse a pattern

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Identifying the Right Pattern

1 pts

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A data visualization dashboard displays the same dataset as both a pie chart and a bar chart. When the underlying data changes, both charts must automatically refresh. Which design pattern is most appropriate?

Façade - to simplify the interface to the charting subsystem

Iterator - to traverse the dataset elements for each chart

Decorator - to add chart formatting features to the basic data object at runtime

Observer - to separate the data object from its multiple display representations and automatically notify all displays when state changes

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Design Patterns - Key Points Summary

1 pts

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Which of the following are TRUE about design patterns? Select ALL that apply.

The general principle of encapsulating experience in a pattern is applicable to any kind of software design, not just object-oriented design

Patterns provide a complete, ready-to-use implementation that can be dropped into any system without modification

Pattern descriptions usually include a graphical model as well as a narrative description

A design pattern is a way of reusing abstract knowledge about a problem and its solution

Patterns rely on object characteristics such as inheritance and polymorphism to provide generality

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Undergraduate Professional

Origin of Design Patterns

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Explanation

The Gang of Four

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Explanation

Four Essential Elements of a Design Pattern

Element

Description

Correct Answer

Explanation

Observer Pattern - Description

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Explanation

Observer Pattern - Four Objects

Object

Role

Correct Answer

Explanation

Observer Pattern - Consequences

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Explanation

Four Common Design Pattern Problems

Problem

Pattern

Correct Answer

Explanation

Patterns vs Component Reuse

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Explanation

Using Patterns in Practice

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Explanation

Identifying the Right Pattern

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Explanation

Design Patterns - Key Points Summary

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Explanation

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