Introduction toObject Oriented

DesignVersion 1.1

Topics

Designing Your Own ClassesAttributes and BehaviorsClass DiagramsSequence Diagrams

Objectives

At the completion of this topic, students should be able to:

Design classes for use in a C# programExplain the difference between a class and an objectExplain what attributes and behaviors areExplain the terms encapsulation and data hidingCreate accurate class diagrams using UML Create a sequence diagram

Motivation

We have worked on a couple of Bowling Team Programs.

We have worked on a couple of Bowling Team Programs.

In these program we had a lot of data associatedWith a bowling team … * bowling scores * names of bowlers * number of people on the teamAnd operations that we wanted to perform on the data * read scores from a file * sort the scores in order * find the average score * output the scores

We have worked on a couple of Bowling Team Programs.

If you wrote any methods to do these operations, youprobably found yourself passing lots of data around asparameters to the methods.

Wouldn’t it be nice if we could keep the data for abowling team all in one place, and make the methodsthat work on the data easier to write?

We can, if we use objects!

Objects

Key Concept

An object often models things in the real world

Bowling Team

Real world objects have attributes

An object’s attributes describe its“state of being”

depending upon the application, some attributes are more important than others

occupation

Average

heightShirtcolor

Real world objects have attributes

For our application, we are interested in

Number of team members

Their bowling scores

The bowlers names

An object also has behaviors

behaviors define how you interact with the object

Find the highest/lowest/average score

Record their

names

Record their scores

Sort the scores

An Object’s Attributes and Behaviors Should Work Together

this is called cohesion

An Object’s Attributes and Behaviors Should Work Together

Cohesion means that methods and data worktogether, for example, read bowling scores from a file.

A Class is a blueprint that a programuses when it creates an object.

A class reserves no space in memory

When an object is created from the classblueprint, memory is reserved to hold the

object’s attributes.

An object is known as an instance of the class.

Each object has it’s own space for data.

A class is said to be an abstraction of thereal world object that we are modeling.

EncapsulationBowling Team object

readFile( )

namesscores

calling method

we should not allow codeoutside of the object to reach in and change the data directly. Instead, we call methods in theobject to do it for us.

member data is declared as private

member methods are declared as public

public and private are called access modifiers

We use a UML Class Diagram to documentthe data and methods contained in

our class.

Bowling Team

A UML class diagram is usedto describe a class in a very preciseway.

A class diagram is a rectangle.

At the top of the rectangle is theclass name. A line separates theclass name from the rest of thediagram.

class BowlingTeam{}Code represented by the UML diagram

BowlingTeam

- numberOfBowlers: intFollowing the class name we writethe data members of the class. Aline separates the data membersfrom the rest of the diagram.

access modifier:+ public- private

data member name

data type

class BowlingTeam{ private int numberOfBowlers;}Code represented by the UML diagram

Following the class name we writethe data members of the class. Aline separates the data membersfrom the rest of the diagram.

class BowlingTeam{ private int numberOfBowlers; private int[ ] scores; private string[ ] names;}Code represented by the UML diagram

BowlingTeam

- numberOfBowlers: int- scores: int[ ]- names: string[ ]

+ ReadScores( ): void

Following the data members, wewrite the member methods.

access modifier + public - private

method name

parameters

return type

class BowlingTeam{ private int numberOfBowlers; private int[ ] scores; private string[ ] names; public void ReadScores( ){ }}Code represented by the UML diagram

BowlingTeam

- numberOfBowlers: int- scores: int[ ]- names: string[ ]

Following the data members, wewrite the member methods.

class BowlingTeam{ private int numberOfBowlers; private int[ ] scores; private string[ ] names; public BowlingTeam(){ } public void ReadScores(){ } public void SortScores(){ } public void DisplayScores( ){ }}Code represented by the UML diagram

+ ReadScores( ): void + SortScores( ): void + DisplayScores( ): void

BowlingTeam

- numberOfBowlers: int- scores: int[ ]- names: string[ ]

It is important that class diagrams be drawnprecisely and that they conform to the form

shown in these examples.

Class diagrams are static. They describe how a class looks.

To show how objects interact with oneanother as a program executes, we

use a Sequence Diagram.

Consider an Application that contains Book objectsAnd Order objects. They might interact as shown:

anOrder aBook

getTitle

getPrice

calcSalesTax

anOrder aBook

getTitle

getPrice

calcSalesTax

The boxes along the top are objects

anOrder aBook

getTitle

getPrice

calcSalesTax

These lines represent messages beingsent from one object to another

anOrder aBook

getTitle

getPrice

calcSalesTax

These lines represent responses(return values)

anOrder aBook

getTitle

getPrice

calcSalesTax

This is a message that the object sends to itself

Practice

Design a class that represents “Integer” objects.

What are the data members of the class?

Design a class that represents “Integer” objects.

Suppose we want methods to set the integer value in the object retrieve the integer value in the object retrieve the reciprocal of the value in the object

Create the UML class diagramInteger

Design a class that represents “StudentInfo” objects.You could use an object of this class to hold thestudent information you print out at the beginningof each of your programming projects.

What are the data members of the class?

Design a class that represents “StudentInfo” objects.

Suppose we want methods to set the name, course, and section values in the object retrieve the name, course and section values from the object output the data in the student object

Create the UML class diagram

StudentInfo

Design a class that represents a car.The important attributes of a car for thisapplication are how much gas it has in its tank,and what kind of mileage (mpg) it gets.

We need member methods (behaviors) that provide the following:- Create a Car object with a given mpg rating- add n gallons of gas to the tank- drive the car y miles- report on how much gas is in the tank

Car

Design a class that represents a student. The important properties of a student for this application are the student’s name, and the scores for two quizzes (10 pts possible on each) and two exams (100 pts possible on each).

We need member methods that• Create a student object – set all scores to zero• Save the score for quiz 1• Save the score for quiz 2• Save the score for exam 1• Save the score for exam 2• Calculates the student’s percent of points possible

Create the UML class diagram

Student

Checking Account

Create the UML class diagram

Checking Account

PayCheck

Create the UML class diagram

Paycheck