OOP Class6

esse quam videri
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Real barking dogs...


an example of how you don't need to know how all of the classes work just how to use them

Shared Members - static members

aka Shared Properties

Static - A type of member modifier that indicates that the member applies to the type rather than an instance of the type

<csharp>public class Dog { //some code

static private int dogCount; // total number of dogs

public Dog() { barkSound = "Woof!!!"; //Add a dog to the total dog count dogCount++; } public Dog(string newName) { name = newName; barkSound = "Woof!!!"; //Add a dog to the total dog count dogCount++; }</csharp>

Static dougCount Example
dogStatic.cs - source

Operator Overloading

You can overload operator in c# just like you overload constuctors

   * Operator Overloading In C# - www.csharphelp.com
   * Operator Overloading in C# - HowToDoThings.com

<csharp>//Overloading unary operators public static return_type operator op (Type t) {

 	// Statements


//Overloading binary operators public static ClassType operator + ( object lhs, object rhs ) {

	ClassType c

//code to implement class addition return c; }</csharp>

dog addition? extra credit

How could you overload + operator so that it returns a new dog when two dogs are added together...

Operator Overloading Fraction Class

<csharp>public static ClassType operator + ( object lhs, object rhs ) {

   ClassType c
   //code to implement class addition
   return c;


Operator also refer to implicit and explicit conversions. Fractions make a good example for opertor overloading. Fraction class

   * Create fractions from two numbers x/y or from whole numbers
   * Convert fractions to whole numbers int
   * Convert fractions to float or double
   * override ToString() to describe Fraction

Fraction Class Example of operator overloading.
fractionConv.cs - source
Fraction class with implicit and explicit conversion
fractionConv_NoTest.cs - source
Fraction class with overridden operators
fractionConvOver.cs - source

In class build a test application does thigs with frations.

http://iam.colum.edu/oop/gbrowser.php?file=/classsource/class5/fractionConv_NoTest.cs fractionDone_NoTest.cs] create a test class that...

  • Creates a fraction out of integers (ie cast int into fractions)
  • Adds, subtracts, and reduces some fractions
  • Creates floting point numbers out of fractions (is cast fraction into double)
  • Checks the eqaulity of some fractions

Class Relationships

Four Class Relation ships

  • Association - 'Uses A'
  • Containment - 'Has A'
  • Inheritance - 'Is A'
  • Interfaces - implements or derives from We'll do this next week in OOP Class6

Association - 'Uses A'

A dog uses a hydrant to relieve them self.

<csharp>//Dog simple class definition public class Dog {

   //some dog code...
   public void Relieve(Hydrant h)
    h.Clean = false;


public class Hydrant {

 public string Color; //the color of the hydrant
 public bool Clean;   //if the hydrant is clean or dirty
 public Hydrant()
   Color = "red";
   Clean = true;
 public override string ToString ()
   if (this.Clean == true)
    return ("The " + this.Color + " hydrant is clean.");
    return ("The " + this.Color + " hydrant is not clean.");


Dog Association example DogHydrant.cs - source

Containment - 'Has A'

A dog has an owner

<csharp>Dog fido = new Dog("fido"); fido.Owner = new Person("Sue");</csharp>

<csharp>//Dog simple class definition public class Dog {

   public string Name;        // the dog's name
   public string BarkSound;    // the sound of the dog's bark
   public Person Owner;    // the dogs owner
   public Dog(string dogName)
       Name = dogName;
       BarkSound = "Woof!!!";
   public string Bark() { 
       string s;
       s = this.Name + " says " + this.BarkSound;
       //Make sure the the dog has an owner
       if (!(this.Owner == null))
          s += "\n" + Owner.Name + " says be quiet.";
       return s;


public class Person

   public string Name;      //the color of the hydrant
   public Person(string newName)
     Name = newName;

Containment example
DogOwner.cs -source


- remember these
from week 2

Lightweight alternatives to classes. Structs do not support inheritance or destructors. Structs are value typed objects similar to ints bool etc... while classes are reference types. Structs are more memory efficient and and faster than classes. Syntax

[ attributes] [access-modifiers] struct identifier [:interface-list {struct members}

<csharp>struct Dog {

public string name;
public string weight;
public int age;


This is a pretty lightweight dog and is pretty useless as a dog (It's can't even bark what fun is that) so I won't make an example.

A good example of a stuct would be and something like a point. There may be many many points in a structure or graph and we would want the points to be a lightweight as possible. Since the point object won't have an methods this is a good time to use a struct.

<csharp>struct Point {

   public int x;
   public int y;
   public Point(int x, int y)
       this.x = x;
       this.y = y;
   public Point Add(Point pt)
       Point newPt;
       newPt.x = x + pt.x;
       newPt.y = y + pt.y;
       return newPt;


and the this keyword

<csharp>//Accessor for private color allow color to be set and return color or 'dirty' + color

   public string Color
           //if current dog isClean the return dogs color
           if (this.isClean == true)
               return color;
           //else return 'dirty' and the dogs color
           else {
               return "dirty " + color;
          color = value;

console /infod/jeff/classSource/class4/dogAccessor.cs - source web /infod/jeff/classSource/class4/dogAccessor.aspx - source

Dog private members, Overloaded with method class definition

<csharp>//Dog private members, Overloaded with method class definition public class Dog {

	private string name;		// the dog's name

private int age; // the dog's age private int weight; // the dog's weight private string barkSound; // the sound of the dog's bark private int barkCount; // how many times the dog has barked

public Dog() { barkSound = "Woof!!!"; } public Dog(string newName) { name = newName; barkSound = "Woof!!!"; } public Dog(string newName, string newBarkSound ) { name = newName; barkSound = newBarkSound; }

public string Name { get { return name; } set { name = value; } } public int Age { get { return age; } set { age = value; } } public int Weight { get { return weight; } set { weight = value; } } public string BarkSound { get { return barkSound; } set { barkSound = value; } } public int BarkCount //you can't set bark count //it only increments from the Bark() method { get { return barkCount; } }

   public string About() 

{ //return a string with some information about the dog

       string about = "";

//this refers to current object about +=("\nThe dogs name is " + this.name + "."); about +=("\nIt is " + this.age + " years old."); about +=("\nIt weighs " + this.weight + " lb(s)."); about +=("\nIts bark sounds like '" + this.barkSound + "'"); about +=("\nIt has barked " + this.barkCount + " time(s)" );

       about += about.Replace("\n","


       return about;


public void Bark() { //make dog bark Console.WriteLine (this.Name + " says " + this.barkSound); //add 1 to the number of times the dog has barked this.barkCount++ ; } public void Eat() { //put eat code here } }</csharp>



In class

Discuss Dog Diagram

OOP Full Dog Diagram

Pair Programming

Pair Programming

We are going to pair off to do our next assignment. Many of the paired programming principles come from XP (http://www.extremeprogramming.org/ Extreeme Progamming)

Pairs are good because

  • Pairs keep each other on track
  • A partner can help when you are stuck
  • Keep each other accountable

Some XP Principles

Fail - If you are having trouble succeeding fail.

Baby Steps - Do the smallest thing that you possible can that moves you in the right direction

If you do decide to dive and conqure the problem please remember that integration process is unpredictable and can be quite difficult. Try to integrate your code often. Try posting up your code and emailing or plan on meeting several times.

When two pair programmers are together one you should sit a one computer (yeah that right two of you at one computer) and one should type while the other watches and reflects. Feel free to slide the keyboard back and forth when someone get tired, stuck or has a new idea.

I would like you and your paired partner to create and demonstate classes in c# from the diagram below.


use Pair Programming to make tests and classes from the following UML

OOP Students Classes Diagram

If you need to ad any supprting methods or properties that are not on the diagram feel free.

Create a UML Diagram of your c# classes (not the tv and radio yeah the pong machine and ninja and kungfumonkey and stuff)


Chapter 2 Introducin the UML in The Unified Modeling Language Users Guided (hand out)

Chapter 4 Classes in The Unified Modeling Language Users Guided (hand out)

quiz #2 next week