Design Class Diagrams

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Design Class Diagrams
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Overview

• To frame our discussion consider

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Outline
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Creating Design Class Diagrams

• Class diagrams are created once
• interaction diagrams are complete
• conceptual model has been refined

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Classes

• Classes are an important building block for
  object-oriented systems. A class is the
  description of a set of objects that share the
  same attributes, operations. Relationships, and
  semantics.
• You use classes to capture the vocabulary of the
  system you are developing.

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Class Diagrams

• A class diagram show a set of classes,
  interfaces, and collaborations and their
  relationships.
• Class diagrams illustrate the static view of a
  system.

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Design Class Diagrams

• A design class diagram illustrates the
  specifications for software classes and
  interfaces in an application.
• Information Content
• classes associations, attributes
• interfaces
• methods
• attributes type information
• navigability
• dependencies

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Important!

• The design class diagram is a model for a
  software entity.

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Making a Design Class Diagram

• Analyze the interaction diagrams to determine the
  classes participating in a software solution.
• Draw them in a class diagram.
• Add the attributes for the classes from the
  conceptual model.
• Add method names by reviewing the interaction
  diagrams.
• Add type information for attributes and methods.
• Add associations required to support visibility.
• Add navigability arrows to indicate the direction
  of visibility.
• Add dependency relationships.

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Example
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Navigability

• Navigability is property of the role which
  indicates that it is possible to navigate across
  the association from objects to other objects.
  Navigability implies visibility.

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Building Systems by Assembling Parts

• Composition
• an organized collection of components interacting
  to achieve a coherent, common behavior
• Association
• a composition of independently constructed and
  externally visible parts.
• Key Language Ideas
• Passing objects by reference, pointer

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Communicating Objects by Reference and by Pointer

• Uses
• result parameters to allow the sender to see the
  changes made to the object by the execution of
  the receiver's method,
• associations to establish connections among
  objects that allow the objects to interact beyond
  the duration of a single method invocation, and
• managers to allow an object of one class to
  create, distribute, or otherwise manage objects
  of another class.

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Composition

• An organized collection of components interacting
  to achieve a coherent, common behavior.

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Forms of Composition

• Association
• A composition of independently constructed and
  externally visible parts
• Aggregation
• A composition that encapsulates (hides) the parts
  of the composition.

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Aggregation

• A composition that encapsulates (hides) the parts
  of the composition.

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Association

• A composition of independently constructed and
  externally visible parts

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Passing Pointers

• // ptrref.cpp Defines the entry point for the
  console application.
• //
• include "stdafx.h"
• include "iostream.h"
• void swap2 (int i, int j)
• void main()
• int a1,b2,c3,d4
• coutltlt"a "ltltaltlt" b "ltltbltltendl
• swap2(a,b)
• coutltlt"a "ltltaltlt" b "ltltbltltendl
• void swap2(int i, int j)
• int t
• ti

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Passing by Reference

• // ptrref.cpp Defines the entry point for the
  console application.
• //
• include "stdafx.h"
• include "iostream.h"
• void swap1 (int i, int j)
• void main()
• int a1,b2
• coutltlt"a "ltltaltlt" b "ltltbltltendl
• swap1(a,b)
• coutltlt"a "ltltaltlt" b "ltltbltltendl
• void swap1(int i, int j)
• int t
• ti
• ij

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Objects for Communication

• Messages can contain parameters. These
  parameters may be simple types - int, float, char
  - or other objects.

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Frame - v1

• class Frame
• private
• BasicFrame frame // hidden
  implementation
• char name // title on
  visible frame
• int xCoord,yCoord // location
  of upper left hand corner
• int height, width // shape of
  the frame
• bool closed
• void CreateIfNeeded()
• public
• Frame(char name, int x, int y, int w, int h)
• Frame(char name, int x, int y)
• Frame(char name)
• Frame()

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Frame - v2

• class Frame
• private char name
• BasicFrame frame
• Location location
• Shape shape
• void CreateIfNeeded()
• public
• Frame(char name, Location loc, Shape sh)
• Frame(char name, Location loc)
• Frame(char name, Shape sh)
• Frame(char name)
• Frame()
• Frame()

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Advantages

• 1. Using Shape and Location capture important
  concepts from the application domain.
• 2. The concepts can communicate important
  information to the reader of the program.
• 3. Provides increased flexibility for the
  programmer.
• 4. Makes certain constructs possible.

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Class Location

• class Location // Version 1
• private
• int currentX, currentY
• public
• Location(int x, int y) // specific
  location
• Location() // default location
• int Xcoord() // return x-axis
  coordinate
• int Ycoord() // return y-axis
  coordinate

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Class Shape

• class Shape // Version 1
• private
• int currentWidth, currentHeight
• public
• Shape(int width, int height) // specific
  shape Shape() // default shape
• int Height() // return height
  
• int Width() // return width

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Constructors

• Frame(char name, Location loc, Shape sh)
• Frame(char name, Location loc)
• Frame(char name, Shape sh)

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Objects by Copy

• Frame smallTop(Small, nearTop, smallSquare)
• nearTop and smallSquare are objects that are
  copied during the construction process.

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Advantages of Copy

• Sender is assured that changes made to the object
  by the receiver do not change the object from the
  senders perspective.

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Limits in Use

• Not appropriate when
• Object must be shared between sender and
  receiver.
• Sender wants the receiver to modify the object.
• Dealing with very large objects.

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Returning Objects

• Objects can be returned from a method.
• Old
• Void TextSize(char msg, int width, int
  height)
• New
• Shape TextSize(char msg)

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Example

• Frame display
• char msgHello There
• Location msgLocation(50,50)
• display.DrawText(msg, msgLocation)
• Shape msgShapedisplay.TextSize(msg)
• display.clear(msgLocation, msgShape)

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Frame Class

• class Frame
• private char name
• BasicFrame frame
• Location location
• Shape shape
• void CreateIfNeeded()
• public
• Frame(char name, Location loc, Shape sh)
• Frame(char name, Location loc)
• Frame(char name, Shape sh)
• Frame(char name)
• Frame()
• Frame()
• void MoveTo(Location loc) //
  change position
• void Resize(Shape sh) //
  change shape
• void Resize( float factor) //
  
• void DrawText(char msg, Location loc) //
  display msg at (x,y)
• Shape TextSize (char msg) //
  find size of msg
• void DrawLine(Location p1, Location p2) //
  draw line from point p1 to point p2

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Problem

• Display a string of characters that appear to
  blink.

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Primitive Message Class

• class PrimitiveMessage
• private
• char msgText
• public
• PrimitiveMessage(char text)
• void SetText(char newText)
• char GetText()
• PrimitiveMessage()

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Frame window("Message Test", Location(100,100),
Shape(200,200)) PrimitiveMessage greeting("Hello
World") Location greetingLocation(20,50) int
onoff void OnStart() window.Clear()
window.DrawText(greeting.GetText(),
greetingLocation) onoff1 void
OnTimerEvent() if (onoff 1) Shape
greetingShape window.TextSize(greeting.GetText()
) window.Clear(greetingLocation,
greetingShape) onoff 0 else
window.DrawText(greeting.GetText(),
greetingLocation) onoff 1 void
OnPaint() if (onoff 1)
window.DrawText(greeting.GetText(),
greetingLocation)
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Responsibilities based on Primitive Message Class
Design
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Message
class Message private char
text // text being displayed
Location location // at this
location Frame frame //
in this window public Message(char
textString, Location whereAt)
Message(Location whereAt) void
DisplayIn(Frame whichFrame) void
MoveTo(Location newLocation) void
SetText(char newText) char GetText()
void Draw() void Clear()
Message()
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Frame window("Message Test", Location(100,100),
Shape(200,200)) Message greeting("Hello World!",
Location(20,20)) int onoff void OnStart()
greeting.DisplayIn(window) greeting.Draw()
onoff 1 void OnMouseEvent(char
frameName, int x, int y, int buttonState) void
OnTimerEvent() if (onoff)
greeting.Clear() onoff 0 else
greeting.Draw() onoff 1 void
OnPaint() if (onoff) greeting.Draw()
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Responsibilities based on Message Class Design
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Blinking Message
class BlinkingMessage private char
text // text being displayed
Location location // at this
location Frame frame // in
this window int visible void
Clear() void Draw() public
BlinkingMessage(char textString, Location
whereAt) BlinkingMessage(Location whereAt)
void DisplayIn(Frame whichFrame) void
MoveTo(Location newLocation) void
SetText(char newText) char GetText()
void Blink() void Redraw() BlinkingMessage()

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Frame window("Message Test", Location(100,100),
Shape(200,200)) BlinkingMessage greeting("Hello
World", Location(20,50)) void OnStart()
window.Clear() greeting.DisplayIn(window)
greeting.Blink() void OnTimerEvent()
greeting.Blink() void OnPaint()
greeting.Redraw() void OnMouseEvent(char
frameName, int x, int y, int buttonState)
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Responsibilities based on Blink Message Class
Design