chapter 4

Question 1

define a design pattern.

Answer 1

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

Question 2

is a design pattern a finished design? why?

Answer 2

• 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

Question 3

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

Answer 3

Christopher Alexander

Question 4

what did the GoF’s book achieve?

Answer 4

initiated the concept of design patterns in software dev’t

Question 5

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

Answer 5

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

Question 6

what are types of DP defined by the GoF?

Answer 6

• creational dp
• structural dp
• behavioral dp

Question 7

describe creational dp

Answer 7

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

Question 8

describe a structural dp?

Answer 8

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

Question 9

describe behavioral dp

Answer 9

• concerned with common communication patterns b/n objects

Question 10

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

Answer 10

creational

Question 11

an adapter is a pattern catalog belonging to ____________ dp?

Answer 11

structural

Question 12

what are characteristics of a dp?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

what are the forms of a dp?

Answer 14

FDR
- delegation
- recursion

Question 15

describe delegation dp form.

Answer 15

• 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

Question 16

describe recursion dp?

Answer 16

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

Question 17

what are the goals of a dp?

Answer 17

GRE
- reuse of designs
- evolution of sw

Question 18

how can we achieve the goals of a dp?

Answer 18

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

Question 19

what are elements of a dp?

Answer 19

NPC are Sus
- name
- problem
- consequence
- solution

Question 20

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

Answer 20

problem

Question 21

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

Answer 21

solution

Question 22

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

Answer 22

consequence

Question 23

explain what scope is in a dp

Answer 23

• 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

Question 24

what scope of dp deals with class inheritance?

Answer 24

class pattern

Question 25

what scope of dp deals with obj composition?

Answer 25

object pattern

Question 26

explain how creational patterns provide flexibility?

Answer 26

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

Question 27

what is the intent of a simple factory pattern?

Answer 27

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

Question 28

describe the adapter design pattern?

Answer 28

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

Question 29

what is the intent of an adapter pattern?

Answer 29

- matches an existing object to a particular interface

Question 30

compare and contrast b/n inheritance and composition.

Answer 30

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

Question 31

give examples of types of behavioral dp.

Answer 31

- observer dp - memento dp

Question 32

what is the observer pattern?

Answer 32

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

Question 33

what are examples of an observer dp?

Answer 33

- broadcasts - publish - subscribe

Question 34

what are the key players in the observer pattern?

Answer 34

- 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

Question 35

describe the memento dp?

Answer 35

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

Question 36

what is memento pattern used for?

Answer 36

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

Question 37

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

Answer 37

- 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 ]

Question 38

what is the intent of the memento dp?

Answer 38

- 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

Question 39

how many interfaces does a memento have?

Answer 39

- 2 - originator sees a wide interface - caretaker sees a narrow interface

Question 40

___________ is responsible for memento's safekeeping?

Answer 40

caretaker

Question 41

what are benefits of a dp?

Answer 41

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