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==abstract class with three virtual methods==

<source lang="csharp">public abstract class MyOperations
{
public virtual void Operation1() {
}
public virtual void Operation2() {
}
public virtual void Operation3() {
}
}
public class MyClass : MyOperations
{
public override void Operation1() { }
public override void Operation2() { }
}
public class MainClass
{
public void DoWork( MyOperations ops ) {
ops.Operation3();
}
}</source>

==Create an abstract class.==

<source lang="csharp">using System;

abstract class Shape {
double pri_width; // private
double pri_height; // private
string pri_name; // private

public Shape() {
width = height = 0.0;
name = "null";
}

public Shape(double w, double h, string n) {
width = w;
height = h;
name = n;
}

public Shape(double x, string n) {
width = height = x;
name = n;
}

public Shape(Shape ob) {
width = ob.width;
height = ob.height;
name = ob.name;
}

public double width {
get { return pri_width; }
set { pri_width = value; }
}

public double height {
get { return pri_height; }
set { pri_height = value; }
}

public string name {
get { return pri_name; }
set { pri_name = value; }
}

public void showDim() {
Console.WriteLine("Width and height are " +
width + " and " + height);
}

// Now, area() is abstract.
public abstract double area();
}

class Triangle : Shape {
string style; // private

public Triangle() {
style = "null";
}

public Triangle(string s, double w, double h) :
base(w, h, "triangle") {
style = s;
}

public Triangle(double x) : base(x, "triangle") {
style = "isosceles";
}

public Triangle(Triangle ob) : base(ob) {
style = ob.style;
}

public override double area() {
return width * height / 2;
}

public void showStyle() {
Console.WriteLine("Triangle is " + style);
}
}

class Rectangle : Shape {
public Rectangle(double w, double h) :
base(w, h, "rectangle"){ }

public Rectangle(double x) :
base(x, "rectangle") { }

public Rectangle(Rectangle ob) : base(ob) { }

public bool isSquare() {
if(width == height)
return true;
return false;
}

// Override area() for Rectangle.
public override double area() {
return width * height;
}
}

class MainClass {
public static void Main() {
Shape[] shapes = new Shape[4];

shapes[0] = new Triangle("right", 8.0, 12.0);
shapes[1] = new Rectangle(10);
shapes[2] = new Rectangle(10, 4);
shapes[3] = new Triangle(7.0);

for(int i=0; i < shapes.Length; i++) {
Console.WriteLine("object is " + shapes[i].name);
Console.WriteLine("Area is " + shapes[i].area());

Console.WriteLine();
}
}
}</source>
<pre class=codeResult>object is triangle
Area is 48
object is rectangle
Area is 100
object is rectangle
Area is 40
object is triangle
Area is 24.5</pre>

==Define abstract class and abstract method==

<source lang="csharp">using System;
abstract class Employee
{
public Employee(string name, float billingRate)
{
this.name = name;
this.billingRate = billingRate;
}

virtual public float CalculateCharge(float hours)
{
return(hours * billingRate);
}

abstract public string TypeName();

private string name;
protected float billingRate;
}
class Manager: Employee
{
public Manager(string name, float billingRate) : base(name, billingRate)
{
}

override public float CalculateCharge(float hours)
{
if (hours < 1.0F)
hours = 1.0F; // minimum charge.
return(hours * billingRate);
}

// This override is required, or an error is generated.
override public string TypeName()
{
return("Manager");
}
}
class Clerk: Employee
{
public Clerk(string name, float billingRate) :
base(name, billingRate)
{
}

override public string TypeName()
{
return("Clerk");
}
}
class Test
{
public static void Main()
{
Employee[] earray = new Employee[2];
earray[0] = new Manager("A", 40.0F);
earray[1] = new Clerk("C", 45.0F);

Console.WriteLine("{0} charge = {1}",
earray[0].TypeName(),
earray[0].CalculateCharge(2F));
Console.WriteLine("{0} charge = {1}",
earray[1].TypeName(),
earray[1].CalculateCharge(0.75F));
}
}</source>
<pre class=codeResult>Manager charge = 80
Clerk charge = 33.75</pre>

==Override abstract method==

<source lang="csharp">using System;
class MainClass
{
static void Main(string[] args)
{
B MyB = new C();
MyB.Display();
}
}
abstract class A
{
public abstract void Display();
}
class B: A
{
public override void Display()
{
Console.WriteLine("Class B"s Display Method");
}
}
class C: B
{
public override void Display()
{
Console.WriteLine("Class C"s Display Method");
}
}
class D: C
{
public override void Display()
{
Console.WriteLine("Class D"s Display Method");
}
}</source>
<pre class=codeResult>Class C"s Display Method</pre>

==Polymorphism and Virtual Functions==

<source lang="csharp">using System;
public abstract class Clock {
public abstract void Play();
}
public class RedClock: Clock {
public override void Play() {
Console.WriteLine("RedClock.Play()");
}
}
public class BlueClock: Clock{
public override void Play()
{
Console.WriteLine("BlueClock.Play()");
}
}
class MainClass
{
public static void CallPlay(Clock ms)
{
ms.Play();
}
public static void Main()
{
Clock ms = new RedClock();
CallPlay(ms);
ms = new BlueClock();
CallPlay(ms);
}
}</source>
<pre class=codeResult>RedClock.Play()
BlueClock.Play()</pre>

==Using Abstract Classes==

<OL><LI>An abstract method is created by specifying the abstract type modifier.</LI><LI>An abstract method contains no body.</LI><LI>An abstract method is not implemented by the base class.</LI><LI>An abstract method is automatically virtual.</LI><LI>A derived class must override it.</LI><LI>The abstract modifier cannot be applied to static methods.</LI><LI>Properties can also be abstract.</LI><LI>A class containing abstract methods must be declared as abstract with the abstract specifier.</LI><LI>There can be no objects of an abstract class.</LI><LI>If a derived class doesn"t implement all of the abstract methods in the base class, then the derived class must also be specified as abstract.</LI></OL>
<p>To declare an abstract method, use this general form:</p>

<source lang="csharp">abstract type name(parameter-list);</source>

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в 15:31, 26 мая 2010

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