CSC 212 –Data Structures

Lecture 8:

Object-Oriented Design

Your Goal When Writing Classes

Good programs workGood programs work Everything else is secondary

Best way for code to work is reusing code Old code has already been debugged Redesigning the wheel wastes time

Great Designs in History

Hide complexity but keep functionalityProvide enough details to use class only

Cars only leave critical controls visible

Encapsulation

Keep class details private Never expose fields

Makes changing their definitions simple Do not specify how methods work

Specify what they do, insteadLeaves you free to rewrite methods

Limiting public info simplifies using classKeeps design general & improves reuse

Great Designs in History

Design should not specify useShould adapt to any environment

Legos place few limits on how used

Abstraction

Describe design in simple, easy languageEach noun should be a classEach action should be its own public method

Use absolutely minimum number of fieldsNo fields for values that can be computedMake type of each field as open as possible

Do not let how enter your design until last step

Great Designs in History

Design should be easy to modifyEnable easy modification as needs change

Quick & easy modifications of components

Modularity

Classes represent single concept/actorUse classes/fields to provide extra details

Each method should do only 1 thingBreak complex actions into small, private

methodsLimit reliance on any implementation details

Always separate input & output from methods that actually do anything I/O details change frequently

Choosing Classes

Examine from functional point of view Questions to ask:

What are the actors? (What interacts in system?)

What does each actor do? Where do actors interact? Whose goals or

needs are being met?

Unified Modeling Language

Illustrate system's classes & relationships Provides class diagram

Class nameAttributes (Fields)Operations (Methods)

Unified Modeling Language

Illustrate system's classes & relationships Provides class diagram

Class nameAttributes (Fields)Operations (Methods)

Basis of tracing formatBecome more useful as

class continues

Unified Modeling Language

Can show relationships between actorsUseful for dividing into fine grained classes

Your Turn

Groups will be changing (starting today) Do not like things getting too static and boring New groups courtesy of random.org

Group 1 Group 2 Group 3

Jaydon Okan Jim

Ryan Alison Debbie

Kim Abe Ben

Derrick Katey Tim

Jake

Before Next Lecture…

Finish lab #2 Finish week #3 assignment Start programming assignment #1

It is due 2 weeks from today Mondays’s lecture discusses inheritance

Read Section 2.2 of the book