Difference between revisions of "OOP Class4"
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In class do phone class. | In class do phone class. | ||
Revision as of 15:06, 28 September 2006
Contents
Classes and Objects
Objects
Object-oriented programs are made up of objects. An object packages both data and the procedures that operate on that data. The procedures are typically called methods or operations. An object performs an operation when it recieves a request(or message) from a client. " - Design Patterns Addison Wesley Reasons for organizing code into Classes and Objects
- avoid spaghetti
- reuse
Classes are sections of code that describe real world objects. Classes define what properties and methods an object contains. Properties define data members of classes and methods define what classes can do. Abstraction
Humans are always abstracting and naming objects. It is how we identify things. Ojbects are indentied by two this properties(what the have) and methods (what they do).
Classes are the unique feature that make a programming language an object oriented programming language.
The hardest part about object oriented programming is choosing how to build and implemt these abstractions. There are many factors that affect these descicions. It can ofetn be very diffuclt to find a balance between all of the factors.
- granulairity
- reusability
- flexabilty
- performance
- portability
Encapsulation
Allows us to use objects with out completely understanding how everything inside the object works. Encapsulation also allows the internal state of objects to be changed easily without affecting other objects or interfaces. For example you don't need to know how the phone system works in order to use a telephone. All you really need to know to use the phone system is how to dial a phone Classes
Classes are used to create objects. a simple example of class syntax in c#
<csharp>public class SomeClass { }</csharp>
class syntax full
[attributes] [access modifiers} class identifier [:base class]
{class body}
Objects are instances of classes. For instance a Dog class may describe what dogs are like. All dogs have specific properties like height, weight, color. Dog also have methods like bark. My dog rover is a specific instance of the dog class.
<csharp>// Instantiate SomeClass objects
// Declare an instance of the SomeClass class
SomeClass firstClass;
// Allocate memory for the dog object firstClass = new SomeClass();
// Declare and Allocate in one like SomeClass secondClass = new SomeClass();</csharp>
The new keyword call the classes constructor which allocated memory on the stack for the object if you do not provide a constructor then a default constructor will be provided. constructor example
<csharp>public class SomeClass
{
public SomeClass()
{
//constructor code
}
}</csharp>
access modifier restrictions (|- |public || No restrictions available to all members of the class. |- |private || Members marked private are only available to methods of that class. |- |protected || Members marked protected are available to methods of thay class and of classes dreived from that class. |- |internal ||Members marked as internal are available to any class within that classes assembly. |- |protected internal ||Same as protected and internal |}
Chair Class
Fields
- int Height
- int NumLegs
- bool HasBack
- bool HeightAdjustable
Methods
- RaiseHeight
- LowerHeight
Chair Class UML
In class do phone class.
Dog Class
Fields
Micorsoft has started call ing public variables fields
- string Name
- int Age
- int Weight
- string BarkSound
Methods
- Bark
- Eat
Dog Class UML
Constructors
A classes constructror is the method that is run when an instance of the class is created. If you do not provide a constructor the complier provides one for you. The contructor is used to initiate all memeber properties. Unlike intrinsic types variables that are not initialized will be set to 0 or "" or null by the compiler in the default constructor. Simple Dog class with constructor
<csharp>//Dog simple class definition public class Dog {
public string Name; // the dog's name
public int Age; // the dog's age public int Weight; // the dog's weight public string BarkSound; // the sound of the dog's bark
public Dog() { BarkSound = "Woof!!!"; }
public void Bark() { //put bark code here } public void Eat() { //put eat code here } }</csharp>
Console Example Dog.cs
Notice that the dog class cannot run. In fact it won't even compile with csc ad an exe. You will get error
error CS5001: Program 'c:\backup\csharp\class4\Dog.exe' does not have an entry point defined
if you try. since the dog class does not have a main method and if we use proper abstaction and ecapsulation then I don't believe that the dog class should have a main method. We will need to write another class that will test drive out dog class. This small program often classed a test or driver class will demonstate how our dog class works. This class will be for demonstation/debug purposes only and will usualy be discarded in the final product.
Notice that this class will also not compile on it's own. You will get
dogTester.cs(19,3): error CS0246: The type or namespace name 'Dog' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(22,3): error CS0103: The name 'milo' does not exist in the class or namespace 'DogTester' dogTester.cs(25,32): error CS0246: The type or namespace name 'milo' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(26,31): error CS0246: The type or namespace name 'milo' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(27,34): error CS0246: The type or namespace name 'milo' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(28,37): error CS0246: The type or namespace name 'milo' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(31,3): error CS0246: The type or namespace name 'Dog' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(32,3): error CS0246: The type or namespace name 'fido' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(33,37): error CS0246: The type or namespace name 'fido' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(34,31): error CS0246: The type or namespace name 'fido' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(35,34): error CS0246: The type or namespace name 'fido' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(36,37): error CS0246: The type or namespace name 'fido' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(39,3): error CS0246: The type or namespace name 'Dog' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(40,3): error CS0246: The type or namespace name 'roover' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(41,3): error CS0246: The type or namespace name 'roover' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(42,3): error CS0246: The type or namespace name 'roover' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(43,37): error CS0246: The type or namespace name 'roover' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(44,31): error CS0246: The type or namespace name 'roover' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(45,34): error CS0246: The type or namespace name 'roover' could not be found (are you missing a using directive or an assembly reference?) dogTester.cs(46,37): error CS0246: The type or namespace name 'roover' could not be found (are you missing a using directive or an assembly reference?)
You can complile the Dog.cs file as a dll (shared library)
csc /t:library /out:Dog.dll Dog.cs
This will produce the Dog.dll file which will allow us to compile the Test class with a refence to the Dog.dll
csc dogTester.cs /reference:Dog.dll
Now we have a working dogTester.exe that is linked to Dog.dll.
Sometimes during devolpment of small classes it is easier to combine the new class and the test class into one file. dogTest.cs
Visual Studio will help us out later by linking all of our references for us. If I don't feel like maintaining a VS project often I will just make a batch file similar to dogTest.bat
There is also an open source build tool NAnt http://nant.sourceforge.net/
OverLoading Contructors
OverLoading a consructor allows object creation to happen in different ways with different parameters. The class can be overloaded to accept different parameters but each contructor method must have a unique parameter signature. Dog class with overloaded constructor
<csharp>//Dog overloaded class definition public class Dog {
public string Name; // the dog's name
public int Age; // the dog's age public int Weight; // the dog's weight public string BarkSound; // the sound of the dog's bark
public Dog() { BarkSound = "Woof!!!"; } public Dog(string newName) { Name = newName; BarkSound = "Woof!!!"; } public Dog(string newName, string newBarkSound ) { Name = newName; BarkSound = newBarkSound; }
public void Bark() { //put bark code here } public void Eat() { //put eat code here } }</csharp>
Console Example dogOverload.cs
Web Example
* dogOverLoad.aspx * dogOverLoadWeb.cs
Properties Private instance data members - accessors
Micorsoft has stared calling private varables 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 helpfull when you want to also do other things when a data member is changed or change the rutern value under certian 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
<csharp>//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;
}
}</csharp>
This keyword
The this keyword used within a class refers to the current instance of the class
<csharp>public Time( int CurrentYear, int CurrentDay) {
this.Year = CurrentYear; this.Day = CurrentDay;
}</csharp>
Here's a class of dogs that return differnt color depending on whether on not they are clean. It uses private private instance data memebrs and the this keyword
<csharp>//Accessor for private color allow color to be set and return color or 'dirty' + color
public string Color
{
get
{
//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;
}
}
set
{
color = value;
}
}</csharp>
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>
console
Real barking dogs...
an example of how you don't need to know how all of the classes work just how to use them
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...
In Class Project
In class build traingle class. Properties
- sideA
- sideB
- sideC
Methods
- Area //A method that reurn the area of the triangle
use Heronian formula which is able to compute the area of a triange by knowing the length of the three sides.
triangle area given a,b,c = sqrt(s(s-a)(s-b)(s-c)) when s = (a+b+c)/2 (Heron's formula)
<csharp>// Heronian formula double s = (a + b + c) / 2.0; double dArea = Math.Sqrt(s*(s-a)*(s-b)*(s-c)); </csharp>
Once you have built the triangle class build a class to test it. The test class should create a triangle with
sideA= 3 sideB= 4 sideC= 5
and then display the area as text in the console.
http://iam.colum.edu/oop/gbrowser.php?file=/classsource/class4/tri_class.cs tri_class.cs]
HomeWork
Read Chapter 08 in learning c#. Read Chapter 2 in Head Start Java (hand out)
Build a class called Television and a class called Radio.
Make sure you include several fields/properties and methods along with a constructor.
Build a test class to demonstate the functionality of your Television and Radio class. 2 pts.
Build a class of your own that describes some real world object then build a test class to demostrate how your class works. 3 pts. It can be anything be creative. Your own class should have private member variables, accessors, methods, and constructors.
