Design Patters

Question 1

Why should we use design patterns?

Answer 1

We should use design patters since they increase code reuse by using common abstraction techniques.

Question 2

What is model view controller

Answer 2

Separates presentation and interaction from system data.
- Model: system data and operations on that data
- View: how the data is presented to the use
- Controller: Manages user interaction (clicks, etc) with data.

Question 3

What is problem description

Answer 3

describes when the design pattern is needed

Question 4

What is solution description:

Answer 4

Explains what the solution is

Question 5

What are the 3 types of design patterns?

Answer 5

Creational, Structural, Behavioral

Question 6

What is creational design patterns

Answer 6

Abstracts the object instantiation process

Question 7

What are some common creational patterns

Answer 7

Abstract factory
builder
factory method
prototype
singleton

Question 8

What is factory method

Answer 8

Problem description:
- use when a class cannot anticipate the objects it must create.
Solution description:
- Defers the responsibility of creating objects to subclasses that know what to create.

example: pizza class has 3 sub classes : cheese, greek, peperoni

Question 9

What is abstract factory

Answer 9

problem description:
- Use when your system must be configured with one of multiple families of objects
Solution description:
- Creates abstractions that hide the configuration details of the object families.

One store will create two types:
- Ny store will create ny borgar and ny pizza
another store will create:
- chicago store will create chicago borgar and chicago pizza

Question 9

What are composite

Answer 9

Problem description: (STRUCTURAL)
- use to allow clietns to treat individual obkects and collections of them identically.
Solution description:
- Use an abstraction to hide the fact that an object is an aggregate of several objects.

Leaf-node relationship, directory and files

Question 10

What is the template method

Answer 10

Problem description: (BEHAVIOURAL)
- Used to share common parts of an implementation while allowing subclasses to refine other parts.
Solution description:
- Common parts are defined in the superclass, which makes calls to abstract methods that deliver the other parts.

example: meal class is abstract, and combo1(), combo2() extend meal. and override the entree(), maincourse() and desert() methods.

Question 11

What is the YAGNI principle.

Answer 11

• “You Aren’t Going to Need It”
• Design for the system you need today
• Revisit design periodically for opportunities to refactor and improve

Question 12

What is cohesion and coupling

Answer 12

Cohesion is the degree to which a module relies on other members within the module to deliver its functionality.
- Keep HIGH

Coupling:
Degree to which a module relies on other modules to deliver functionality
- keep LOW

Question 13

What are Structural patters

Answer 13

Structural:
Abstracts how classes and objects are composed to build larger structures

Question 14

What are Behavioural patters

Answer 14

Behavioural:
Abstracts algorithms and assignment of responsibility among objects

Question 15

What are 7 types of structural patterns

Answer 15

skip

Question 16

What is cohesion

Answer 16

Degree to which a module relies on other members within the module to deliver its functionality
Desirable to keep HIGH

Question 17

What is coupling

Answer 17

Degree to which a module relies on other modules to deliver functionality
Desirable to keep LOW

Question 18

What is a schizo class

Answer 18

Problem description:
A class that contains disjoint sets of public methods that are used by disjoint sets of client classes
Solution description:
Refactor each set of methods into individual classes

Question 19

What is a blob class

Answer 19

Name:
Blob (aka: god class)
Problem description:
A large class that is lacking cohesion or makes most of the processing decisions
Solution description:
Refactor Blob classes into a series of more cohesive classes