Class Design

What are the 5 steps of creating software?

Establishing requirements

Creating a design

Implementing the code

Testing the implementation

Maintaining the implement

Explain Establishing requirements (Steps of creating software) (2)

Specifying what a program must accomplish

• Descriptions of UI

• Initial requirements are critiqued/modified/expanded

What does careful attention in the “establishing requirements” stage save?

Time and expense

Explain Creating a Design (Steps of creating software) (2)

Specifies how a program will accomplish its requirements.

• Includes 1 or more algorithms.

• Algorithms may be expressed in pseudocode

What does design establish in object-oriented development? (3)

Classes & Objects. Methods & Data required. Modeled using UML diagram

Explain Implementing The Code (Steps of creating software) (2)

• Least creative step

  • Focuses on style guidlines and documentation

Explain Testing The Implementation (Steps of creating software) (1)

Testing execution with various inputs to find errors

What is debugging?

Discovering causes of errors and fixing problems

What is unit testing?

Testing individual methods

What is integration testing?

Testing how different classes work together

What is regression testing?

Used to ensure existing functionality is maintained after changes

What is performance testing?

Checking speed/security/usability

Explain MaintainingThe Implementation (Steps of creating software) (2)

Modifying code to improve software by fixing deficiencies and adding features

What does UML Digrams stand for?

Unified Modelling Language Diagrams

Function of Use Case Diagrams

Indentifies what the system must do before deciding how to build it

Function of Activity Diagrams

Describe the flow of actions (sequential and parallel)

Function of State Diagrams

Describe the different states of a component and how it changes based on events

Function of Class Diagrams

Detail class attributes (data) and behaviours (methods)

What kind of diagram is this?

Activity diagram

What is a decision node?

Diamond shape. Allows for different logic paths

What is encapsulation?

Client sees result while code handles math and logic

What diagram is this?

State diagram

What diagram is this?

Use case diagram

What are actors? (3)

Humans. Organisations. External Appliances

Function of class diagrams

Defines static state and dynamic behaviour

What is “this” used for in code?

Refers to current object instance and used to distinguish instance fields and local parameters

What does “this.variable” in code referred to?

Disambiguating shadowed variable

Can class diagrams show multi-class interactions?

Yes

What is Class Communication?

Classes interact via well-defined public interfaces

What is low-coupling?

Changes in one class do not break other communicating classes if the interface remains consistent

What is The Maintenance Trap?

Bad design problems usually surface during the maintenance phase when a new feature or bug fix is required

What is used to evaluate quality?

Coupling and Cohesion

What is coupling?

Degree of interconnectedness between classes

Is high coupling good or low coupling?

Low coupling

What is high coupling?

When changes in one class necessitate changes in several others

Why is high coupling bad (2)

Creates ripple effect. Difficult to maintain and test

Benefit of low coupling?

Enhances reusability and readability

What reduces coupling between classes?

Encapsulation

What should objects be?

Self governing: changes to state only occur via object’s own methods

What is the Internal View?

Hidden properties and logic (implementation)

What is the External View?

Services provided to others (interface)

What do visibility modifiers help with?

Encapsulation

Private accessibility modifier

Accessible only inside the class (protects integrity)

Public accessibility modifier

Accessible from anywhere (defines interface)

What is cohesion?

The diversity of tasks a code unit handles

What is low cohesion?

One unit handles many unrelated tasks

Negative of low cohesion

Dificult to understand/reuse/maintain

What is high cohesion?

One unit does one cohesive task

How does high cohesion save time during the management phase? (3)

• Facilitates the reuse of methods.

• Reduces regression as changes are isolated preventing them from affecting other parts of the code.

• Robust evolution (makes adding new features easier)