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Software Design Arch > chapter 4 > Flashcards

chapter 4 Flashcards

1
Q

define a design pattern.

A

pattern is a general repeatable solution to commonly occurring problem in OO software design [ context ].

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2
Q

is a design pattern a finished design? why?

A
  • its not a finished design that can be transformed into a code, but rather a template for how to solve a problem.
    Example:
  • house blueprint
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3
Q

the book; The Gang of Four’s book was written based on the principles of _____________ ?

A

Christopher Alexander

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4
Q

what did the GoF’s book achieve?

A

initiated the concept of design patterns in software dev’t

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5
Q

according to the GoF, a design pattern should be based on which OO principles?

A
  • program to an interface not an implementation
  • favor object composition over inheritance
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6
Q

what are types of DP defined by the GoF?

A
  • creational dp
  • structural dp
  • behavioral dp
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7
Q

describe creational dp

A
  • creates objs in a manner suitable for the situation.
  • deals with obj instantiation
  • hides creation logic, instead of just using the new operator
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8
Q

describe a structural dp?

A
  • deals with r/n ships b/n entities, to make it easier for them to work together
  • concerned with classes and object composition
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9
Q

describe behavioral dp

A
  • concerned with common communication patterns b/n objects
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10
Q

a factory method is a pattern catalog belonging to ____________ dp?

A

creational

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11
Q

an adapter is a pattern catalog belonging to ____________ dp?

A

structural

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12
Q

what are characteristics of a dp?

A

LV R
- levels - decomposition of patterns
- view points - description of patterns
- roles - “players” in pattern usage

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13
Q

what is the d/ce b/n static and dynamic viewpoints?

A
  • static vp - describes class models [ building blocks ]
  • dynamic vp - seq diagrams
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14
Q

what are the forms of a dp?

A

FDR
- delegation
- recursion

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15
Q

describe delegation dp form.

A
  • a mechanism in w/c an obj delegates a req to another obj
  • the other obj carries out the req on behalf of the original obj
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16
Q

describe recursion dp?

A
  • a mechanism in w/c part of the pattern uses itself
    Example:
  • GUIs where windows within windows are allowed
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17
Q

what are the goals of a dp?

A

GRE
- reuse of designs
- evolution of sw

18
Q

how can we achieve the goals of a dp?

A

by reducing dependencies among components
- program to interfaces not implementations
- favor obj composition not inheritance
- use delegation

19
Q

what are elements of a dp?

A

NPC are Sus
- name
- problem
- consequence
- solution

20
Q

____________ is an element of a dp, that describes when to apply a pattern?

A

problem

21
Q

____________ is an element of a dp, that describes elements that make up the pattern, their r/n ship and responsibilities?

A

solution

22
Q

____________ is an element of a dp, that describes results and the tradeoffs of applying the pattern?

A

consequence

23
Q

explain what scope is in a dp

A
  • describes what the pattern applies to
    Example:
  • class patterns : focus on r/n ships b/n classes and subclasses
  • obj patterns : focus on r/n ships b/n objs
24
Q

what scope of dp deals with class inheritance?

A

class pattern

25
Q

what scope of dp deals with obj composition?

A

object pattern

26
Q

explain how creational patterns provide flexibility?

A
  • the pattern creates objs for us, instead of us instantiating objs
  • hence program has flexibility in deciding which objs need to be created
27
Q

what is the intent of a simple factory pattern?

A
  • abstracts logic of object creation [ simpleBurger Factory ]
  • refers to newly created obj through a common interface [ Burger burger ]
28
Q

describe the adapter design pattern?

A

the example about xml and json
- is a structural dp that allows incompatible interfaces to collaborate with one another

29
Q

what is the intent of an adapter pattern?

A
  • matches an existing object to a particular interface
30
Q

compare and contrast b/n inheritance and composition.

A

Inheritance : aka white box
- all subclasses are dependent [ tightly coupled ] with the parent class
- unnecessarily complex
- can easily break code upon change

Composition : aka black box
- one class can use another
- loosely coupled
- implementations can be easily replaced with out breaking code

31
Q

give examples of types of behavioral dp.

A
  • observer dp
  • memento dp
32
Q

what is the observer pattern?

A

remember the store, owner and customer
- is a behavioral dp that defines a 1-to-many r/n ship b/n objects [ subject and observer ]
- so when a subject changes state, all observers are notifies and updated

33
Q

what are examples of an observer dp?

A
  • broadcasts
  • publish - subscribe
34
Q

what are the key players in the observer pattern?

A
  • subject / publisher [ list of sub, sub and unsub methods ]
  • object / subscriber - an updating interface for obj that get notified upon changes to a subject
  • concrete subject
  • concrete observer - implements update interface
35
Q

describe the memento dp?

A

is a behavioral dp that delegates the task of creating the State of Snapshots to the actual owner of that state.

  • prevents other objects from trying to copy the state of the class from outside of the class
36
Q

what is memento pattern used for?

A
  • is used to restore the state of an object to a previous state
    Example:
  • Ctrl + Z in editors
  • check points
37
Q

what are the actor classes used in memento dp? describe what they do.

A
  • Memento - contains current state of an object
  • originator [ TextArea ] - creates and stores states in the Memento object [ snapshots ]
  • Caretaker [ editor ] - restores object state from the Memento object [ list of snapshots yizo vibe ]
38
Q

what is the intent of the memento dp?

A
  • captures and externalizes an objects state with out violating its encapsulation
  • since it can only be accessed by the class its contained under
  • it will not expose internal data of an object to objects outside the class
39
Q

how many interfaces does a memento have?

A
  • 2
  • originator sees a wide interface
  • caretaker sees a narrow interface
40
Q

___________ is responsible for memento’s safekeeping?

A

caretaker

41
Q

what are benefits of a dp?

A

AFFRII
- provides access from experts to non experts
- facilitates comm
- facilitates design improvement
- reuse of successful designs
- improve design understandability
- improve design doc

Software Design Arch (8 decks)

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