ECE 264Object-Oriented

Software Development

Instructor: Dr. Honggang WangFall 2012

Lecture 15: Class diagrams; class relationships

Lecture outline Announcements / reminders

Lab 5 to be posted Tuesday; due 10/22 Today

UML class diagrams Class relationships

Association, aggregation, and composition Composition and initialization lists Modeling in UML

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UML class diagrams UML class diagram contains 3 boxes

First contains class name Second contains data members Third contains member functions

For member data/functions Can list names only, but types/arguments preferred

Format: name : type Same format for data/functions—type is fn. return type With function arguments, only types needed

+ indicates public - indicates private

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Example: Class diagramPoint

-xCoord: double-yCoord: double+Point()+Point(double, double)+setX(double) : void+setY(double) : void+getX() : double+getY() : double+printPoint(ostream &) : void+movePoint(double, double) : void

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Example 2 Say we have a class to represent a time in

24-hour format; this class should contain: The number of hours and minutes Default and parameterized constructors Set/get functions for all data members A private “helper” function, extraF, that is only

used in other member functions, takes no arguments, and returns an integer

Draw a class diagram for this class Using your class diagram, write a header file

for the class

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Example 2: Time classTime

-hours : int-minutes : int+Time()+Time(int, int)+setHours(int) : void+setMinutes(int) : void+getHours() : int+getMinutes() : int-extraF() : int

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Example 2: Time.hclass Time {public:

Time();Time(int h, int m);void setHours(int newH);void setMinutes(int newM);int getX();int getY();

private:int hours, minutes;int extraF();

};

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Class relationships Typically have multiple objects in program Different types may interact with one another

Basic interactions: association One class “uses” another in some way Example (from text): ATM “executes” a Withdrawal

Classes as data members: “has a” Two such relationships: aggregation and composition

Difference: are object lifetimes linked? In composition, if “parent” is destroyed, “child” is as well Same is not true for aggregation

Can model relationships in UML

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Composition example A rectangle is a shape that has a:

point of origin width height

Can implement this concept by defining a class named Rectangle Methods might include:

Accessing width/height/origin Setting width/height/origin Moving rectangle (i.e., relocating origin) Calculating area

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Basic UML composition diagram Shows that

Rectangle “has a” Point

The 1 indicates Rectangle contains 1 point

The closed diamond indicates composition Objects share “life

cycle”—destroy rectangle, and you destroy Point

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Rectangle

Point

1

-double width-double height-Point origin

+Rectangle() +setOrigin()+getHeight() +setWidth()+getOrigin() +move()+getWidth() +area()+setHeight()

1

1

Example code: setOrigin()void Rectangle::setOrigin(double x, double y) {

origin.xCoord = x; // Won’t workorigin.setY(y);

}

Example shows two different ways of accessing elements of Point Directly changing private data still won’t work Must use set functions

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Composition example Write code for:

Rectangle::getOrigin(); Rectangle::setOrigin();

Rewrite example on previous slide to take a Point object, p, as an argument to the function

Rectangle::move(); Takes two arguments—distances to move the x and y

coordinates of the origin

Note that (most) types are purposely not given

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Example solutionsPoint Rectangle::getOrigin() {return origin;

}

void Rectangle::setOrigin(Point p) {origin.setX(p.getX());origin.setY(p.getY());

}

void Rectangle::move(double addX, double addY) {origin.move(addX, addY);

}

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Modeling association

Extension of class diagram When showing relationships, do not need to show all members of class

Association contains unidirectional arrow Can specify how many objects are involved

“1 ATM object executes 0 or 1 Withdrawal objects” Possible multiplicities

Constant values: 0, 1, m (integer) Either-or: m,n “m or n”

0..1 is special case Unknown value: * (non-negative integer) Ranges:

m..n “at least m but not more than n” 0..* “zero or more” 1..* “one or more”

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Modeling composition/aggregation

Composition indicated by solid diamonds attached to association lines Aggregation would use hollow diamonds

Properties Only one class represents whole Parts may only belong to one whole at a time

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Initialization lists How would we write Rectangle

constructor(s)? Ideally, we’d like to call Point constructor as well Use an initialization list

Explicitly calls constructors for member data Requires parameterized constructor to be defined Can be used for predefined types as well

Example:

Rectangle::Rectangle() : height(1), width(1), origin(0,0)

{}

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Final notes Next time

Arrays, vectors, and other container classes Acknowledgements: this lecture borrows

heavily from lecture slides provided with the following texts: Deitel & Deitel, C++ How to Program, 8th ed. Etter & Ingber, Engineering Problem Solving with

C++, 2nd ed.

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