OOP Class11
Duck Study
Contents
Private instance data members - accessors
Microsoft has stared calling private variables with accessors Properties
Private class memebers the use get and set keyword to set and retrieve data. Get and set are known as accessor methods private members are helpful when you want to also do other things when a data member is changed or change the rutern value under certain conditions. C# Programmer's Reference - Accessors http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csref/html/vclrfaccessorspg.asp. Lastly accessor also make read only and write only variables possible
//private string color read/write
private string color;
public string Color
{
get
{
return color;
}
set
{
color = value;
}
}
//private string color read only
private string color;
public string Color
{
get
{
return color;
}
}
Another property that is a good candidate for a private instance data member is the dogs age
private string age;
public int Age
{
//age can only be accessed with get there is no set accessor
//age must be set with HappyBirthday()
get
{
return age;
}
}
public int HappyBirthday()
{
age++;
return age;
}
Problems with inheritance
Rocket Ducks!!!!
public class Duck
{
public string DuckSound;
public string Fly()
{
return string.Format("(0) us flying", this);
}
public string Quack()
{
return this.DuckSound;
}
}
|
public class Rocket
{
public bool IsIgnited;
public string Fly()
{
return string.Format("(0) us flying", this);
}
public void Launch()
{
this.IsIgnited = true;
}
}
|
Notice both have a Fly() method.
I want a RocketDuck. One that can fly with wings or rockets. I could try inheritance...
public class Duck : Rocket
{
public string DuckSound;
...
Now I get a warning
Warning 1 'FlyingDucks.Duck.Fly()' hides inherited member 'FlyingDucks.Rocket.Fly()'
This doens't work | Neither does this |
What we need is multiple inheritance or Interfaces. C# doesn't have multiple inheritance so let's try interfaces.
Interfaces
IFlyable
interface IFlyable
{
int CurrentAltitude { get; set; }
bool IsFyling();
void FlyUP();
void FlyDown();
void Fly();
}
Implementation
class Helicopter : IFlyable
{
protected int currentAltitude; //Private instance data member
public bool IsFyling { get; set; }
public Helicopter()
{
this.CurrentAltitude = 0;
}
public int CurrentAltitude //Accessor
{
get
{
return currentAltitude;
}
set
{
currentAltitude = value;
}
}
public void FlyUP()
{
this.CurrentAltitude++;
}
public void FlyDown()
{
this.CurrentAltitude--;
}
public void Fly()
{
this.IsFyling = true;
}
}
Controls is an example of good inheritance
http://iam.colum.edu/oop/classsource/class11/controls.aspx
see
Hierarchy
Object ---> Control---> WebControl---> BaseDataBoundControl ---> DataBoundControl --->ListControl ---> DropDownList
Strategy Pattern
http://www.dofactory.com/Patterns/PatternStrategy.aspx
Strategy Pattern
- Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Ducks From Book
http://iam.colum.edu/oop/browser/browser.aspx?f=/classsource/class11/Duck
http://www.dofactory.com/Patterns/PatternStrategy.aspx
Pretty good example of the strategey method in action.
Phones
http://iam.colum.edu/oop/classsource/class12/ConsoleApplicationPhoneNoInterface.zip
Review Homework
Problems
Phone interface
Look as phone project. Discuss polymorphic phones interchangeability. Look for possible interfaces to extract.
Homework
Extract interfaces for phone class. Make a web interface for the phone classes.
You should be able to choose an phone type and then dial it and send messages if it is ITxtable.
http://iam.colum.edu/oop/classsource/class12/ConsoleApplicationPhoneNoInterface.zip