OO Objects (PPT 9-10)

Question 1

What is a class?

Answer 1

Represents all objects within the problem domain that share the characteristics and behaviour of a concept, e.g. a customer

Question 2

What is an object?

Answer 2

It is an instance of a class/concept. All instances of the object share the same attributes

Question 3

What can objects do?

Answer 3

They can provide and perform operations. This allows them to be called upon to do specific duties. They can also collaborate and send messages between other objects

Question 4

What is a class diagram?

Answer 4

It is a visual model of the problem domain and a potential design for the system. Allows us to capture our understanding, test and communicate our thoughts

Question 5

What types of things can be classes?

Answer 5

• Tangible or physical things
• Types of roles played by people, places or organisations
• Incidents or events
• Transactions
• Policies, processes and/or algorithms
• Specifications

Question 6

What are Specification Classes?

Answer 6

They are general classes usually used for inventory systems, such as products. Can distinguish between objects which provide a specification and objects which meet the specification

Question 7

What are some techniques for identifying classes?

Answer 7

• Larmans Conceptual Class Categories

- Noun analysis

Question 8

What are the class categories in Larmans?

Answer 8

• Physical things
• Types of people
• Places
• Catalogues, containers
• Transactions
• Product or service related to transaction
• Other systems we integrate with
• Other

Question 9

What are some ways we can refine noun candidate classes?

Answer 9

Redundant Concepts
-Two nouns refer to the same concept
Irrelevant Concepts
-Outside the scope of the system
Vague or Too broad in scope
Attributes of another class

Question 10

What are the three types of class we may have?

Answer 10

• Entity class
• Boundary class
• Control class

Question 11

What is an entity class?

Answer 11

It is a class which represents things which are long lived, application independent and usually real world entities

Question 12

What is a boundary class?

Answer 12

It is a class which handles communication between the external world and the system. May also link to other systems or electro-mechanical systems

Question 13

What is a control class?

Answer 13

It is a class which coordinates events within the system. It delegates and knows when to do things, not how

Question 14

What are analysis patterns?

Answer 14

They are distilled experiences of recurring problems during the analysis of systems

Question 15

Give an example of an analysis pattern

Answer 15

The quantity pattern: Is a cost a more complex concept than it seems?

Question 16

What is responsibility driven design?

Answer 16

Classes should have a single, clearly defined responsibility. Their attributes and operations should be strongly focused around this purpose

Question 17

What are CRC cards?

Answer 17

They are Class-Responsibility-Collaboration Cards. State the name of the class, what it does and what it works with

Question 18

What are some advantages of CRC cards?

Answer 18

Physicality
-Hold them, move them around a desk, protect them
-Pretend that you are the system
Informal
-They seem more moveable in the face of change
Portable, Inexpensive
-Post it notes, white board, etc
Qualitative Issues
-Points of difficulty, bottlenecks, gaps, new responsibilities
Size of cards
-Forces classes to have clearly defined responsibilities