Mohammad Shaker
mohammadshaker.com
C# Programming Course
@ZGTRShaker
2011, 2012, 2013, 2014
C# Starter
L02 – Classes, Poly...
Today’s Agenda
• Classes
• Inheritance
• Polymorphism
• Versioning
• Interfaces
• Reference types VS Value types
Object oriented programming (OOP) is a way
of programming where you create chunks of
code that match up with real world ob...
Classes
A Class
• Let’s create a Player
• And a Constructor
class Player
{
private string name;
private int score;
private int liv...
Classes and Objects
Who is Who?
Objects appear only at Runtime
this Keyword
this Keyword
What is it?
this Keyword
A pointer pointing on the object itself at runtime
this Keyword Usage
• Name hiding and clarity
• Passing Player instance at runtime to other object.
• Cloning the Player ob...
Static Keyword
What is it?
Destructors
Destructor
• Correspond to finalizers in Java.
• Called for an object before it is removed by the garbage collector.
• No ...
Inheritance
Constructors and Inheritance
using System;
public class ParentClass
{
public ParentClass()
{
Console.WriteLine("Parent Constructor.");
}
public void pr...
using System;
public class ParentClass
{
public ParentClass()
{
Console.WriteLine("Parent Constructor.");
}
public void pr...
using System;
public class ParentClass
{
public ParentClass()
{
Console.WriteLine("Parent Constructor.");
}
public void pr...
using System;
public class ParentClass
{
public ParentClass()
{
Console.WriteLine("Parent Constructor.");
}
public void pr...
public class Parent
{
string parentString;
public Parent()
{
Console.WriteLine("Parent Constructor.");
}
public Parent(str...
public class Parent
{
string parentString;
public Parent()
{
Console.WriteLine("Parent Constructor.");
}
public Parent(str...
public class Parent
{
string parentString;
public Parent()
{
Console.WriteLine("Parent Constructor.");
}
public Parent(str...
Polymorphism
public class DrawingObject
{
public virtual void Draw()
{
Console.WriteLine(
"I'm just a generic drawing object.");
}
}
pu...
public class DrawingObject
{
public virtual void Draw()
{
Console.WriteLine(
"I'm just a generic drawing object.");
}
}
pu...
public class DrawingObject
{
public virtual void Draw()
{
Console.WriteLine(
"I'm just a generic drawing object.");
}
}
pu...
class Program
{
static void Main(string[] args)
{
DrawingObject[] dObj = new DrawingObject[4];
dObj[0] = new Line();
dObj[...
class Program
{
static void Main(string[] args)
{
DrawingObject[] dObj = new DrawingObject[4];
dObj[0] = new Line();
dObj[...
public class DrawingObject
{
public DrawingObject(string objectName)
{
}
public virtual void Draw()
{
Console.WriteLine("I...
public class DrawingObject
{
public DrawingObject(string objectName)
{
}
public virtual void Draw()
{
Console.WriteLine("I...
public class DrawingObject
{
public DrawingObject(string objectName)
{
}
public virtual void Draw()
{
Console.WriteLine("I...
public class DrawingObject
{
public DrawingObject(string objectName)
{
}
public virtual void Draw()
{
Console.WriteLine("I...
public class DrawingObject
{
public DrawingObject(string objectName)
{
}
public virtual void Draw()
{
Console.WriteLine("I...
Polymorphism
Polymorphism
Polymorphism
public class DrawingObject
{
public DrawingObject(string objectName)
{
Console.WriteLine(objectName);
}
public virtual voi...
public class DrawingObject
{
public DrawingObject(string objectName)
{
Console.WriteLine(objectName);
}
public virtual voi...
public class DrawingObject
{
public DrawingObject(string objectName)
{
Console.WriteLine(objectName);
}
public virtual voi...
public class DrawingObject
{
public DrawingObject(string objectName)
{
Console.WriteLine(objectName);
}
public virtual voi...
public class DrawingObject
{
public DrawingObject(string objectName)
{
Console.WriteLine(objectName);
}
public virtual voi...
Polymorphism
Polymorphism
public class DrawingObject
{
public DrawingObject(string objectName)
{
Console.WriteLine(objectName);
}
public virtual voi...
public class DrawingObject
{
public DrawingObject(string objectName)
{
Console.WriteLine(objectName);
}
public virtual voi...
Abstract Classes
Abstract Classes
• Abstract methods do not have an implementation.
• Abstract methods are implicitly virtual.
• If a class...
sealed and internal classes
sealed: can’t be extended (Java’s final)
internal: can’t be used in other namespaces
Versioning
class DerivedClass: BaseClass
{
public override string Meth1()
{
return "MyDerived-Meth1";
}
public new string Meth2()
{
r...
class DerivedClass: BaseClass
{
public override string Meth1()
{
return "MyDerived-Meth1";
}
public new string Meth2()
{
r...
class DerivedClass: BaseClass
{
public override string Meth1()
{
return "MyDerived-Meth1";
}
public new string Meth2()
{
r...
class DerivedClass: BaseClass
{
public override string Meth1()
{
return "MyDerived-Meth1";
}
public new string Meth2()
{
r...
class DerivedClass: BaseClass
{
public override string Meth1()
{
return "MyDerived-Meth1";
}
public new string Meth2()
{
r...
Multiple Inheritance?
C#.NET doesn't allow it, Why?
Multiple Inheritance?
C#.NET doesn't allow it
C++.NET doesn’t allow it
Java doesn’t allow it
C++, as you know, allows it
However, C# allow
multiple interfaces
However, C# allow
multiple interfaces
But what are they?
Interfaces
Interfaces :D
Interfaces – The concept
Interfaces VS Abstract Classes
Interfaces
• An interface contains only the signatures of methods, delegates or events.
• The implementation of the method...
When to use?
(An Example)
Consider a Human, an Animal and a Car Class, where they all implement a crazy method called
ConsumeWater().
If we have man...
SomeObject
Human Animal Car
And they they can’t be subclassed from one particular abstract/base class like this:
SomeObject
Human Animal Car
And they they can’t be subclassed from one particular abstract/base class like this:
Because t...
If we have many objects of each type of Human, Animal and Car and we want to call
ConsumeWater() for all objects of Human,...
If we have many objects of each type of Human, Animal and Car and we want to call
ConsumeWater() for all objects of Human,...
Now we can add all objects to a common list of IWaterable and just call ConsumeWater()
for each IWaterable object (they ar...
Interfaces – the Code
Interfaces – the Code
Public interface IWaterable
{
public void ConsumeWater();
}
Interfaces – the Code
Public interface IWaterable
{
public void ConsumeWater();
}
Public class Human: IWaterable
{
public ...
Interfaces – the Code
Public interface IWaterable
{
public void ConsumeWater();
}
Public class Human: IWaterable
{
public ...
Interfaces – the Code
Public interface IWaterable
{
public void ConsumeWater();
}
Public class Human: IWaterable
{
public ...
Interfaces – the Code
Public interface IWaterable
{
public void ConsumeWater();
}
Public class Human: IWaterable
{
public ...
Interfaces
• An interface can be a member of a namespace or a class and can contain
signatures of the following members:
–...
Reference VS Value Types
using System;
class Program
{
static void Main()
{
float lengthFloat = 7.35f;
// lose precision - explicit conversion
int ...
using System;
class Program
{
static void Main()
{
float lengthFloat = 7.35f;
// lose precision - explicit conversion
int ...
Reference VS Value Types
• Reference type
• variables are named appropriately (reference) because the variable holds a ref...
using System;
class Employee
{
private string _name;
public string Name
{
get { return _name; }
set { _name = value; }
}
}...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
class Program
{ static void Main()
{
Employee joe = new Employee();
joe.Name = "Joe";
Employee bob = new E...
Reference Types
• The following types are reference types:
• arrays
• class
• delegates
• interfaces
Value Types
Value Types
• A value type
– variable holds its own copy of an object and when you perform assignment from one value
type ...
Value Types
• A value type
– variable holds its own copy of an object and when you perform assignment from one value
type ...
struct Height
{
private int m_inches;
public int Inches
{
get { return m_inches; }
set { m_inches = value; }
}
}
Value Typ...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
class Program
{
static void Main()
{
Height joe = new Height();
joe.Inches = 71;
Height bob = new Height();
bob.Inches = 5...
Value Types
• The following types are value types:
– enum
– struct
Classes and Structs
Classes
• Reference Types
• (objects stored on the heap)
• support inheritance
• (all classes are deri...
Creating a Class Library Project for Your
Project’s Logic
Now write all your code in the Class Library project and reference it in your presentation layer project
Adding References to Other Projects to
Your Project
Adding References to Your Project
The Principles
• Single Responsibility Principle: design your classes so that each has a single purpose
• Open / Closed Pr...
is the process of validating the correctness of a small section of code. The target code may be a method within
a class, a...
Question #1
public class BaseClass
{
public virtual string Meth1()
{
return "BaseClass-Meth1";
}
public string Meth2()
{
r...
Question #1
public class BaseClass
{
public virtual string Meth1()
{
return "BaseClass-Meth1";
}
public string Meth2()
{
r...
Question #2
class Class1 { }
class Class2 : Class1{ }
class Class3 { }
public class TestingClass
{
public static void Test...
Question #2
class Class1 { }
class Class2 : Class1{ }
class Class3 { }
public class TestingClass
{
public static void Test...
public interface IsBaseTest
{
void Point1(object obj);
}
public class IsTest
{
public static void Point1(object obj)
{
Con...
public interface IsBaseTest
{
void Point1(object obj);
}
public class IsTest
{
public static void Point1(object obj)
{
Con...
That’s it for today!
Hope you enjoy it!
C# Starter L02-Classes and Objects
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C# Starter L02-Classes and Objects

  1. 1. Mohammad Shaker mohammadshaker.com C# Programming Course @ZGTRShaker 2011, 2012, 2013, 2014 C# Starter L02 – Classes, Polymorphism, Versioning, Interfaces, Reference and Value Types
  2. 2. Today’s Agenda • Classes • Inheritance • Polymorphism • Versioning • Interfaces • Reference types VS Value types
  3. 3. Object oriented programming (OOP) is a way of programming where you create chunks of code that match up with real world objects.
  4. 4. Classes
  5. 5. A Class • Let’s create a Player • And a Constructor class Player { private string name; private int score; private int livesLeft; } class Player { private string name; private int score; private int livesLeft; public Player(string name) { this.name = name; } public Player(string name, int startingLives) { this.name = name; livesLeft = startingLives; } }
  6. 6. Classes and Objects Who is Who?
  7. 7. Objects appear only at Runtime
  8. 8. this Keyword
  9. 9. this Keyword What is it?
  10. 10. this Keyword A pointer pointing on the object itself at runtime
  11. 11. this Keyword Usage • Name hiding and clarity • Passing Player instance at runtime to other object. • Cloning the Player object (instance at runtime) into another Player object (in constructor.) public Player(string name) { this.name = name; } public Player(string name, int startingLives) { this.name = name; livesLeft = startingLives; }
  12. 12. Static Keyword What is it?
  13. 13. Destructors
  14. 14. Destructor • Correspond to finalizers in Java. • Called for an object before it is removed by the garbage collector. • No public or private. • Is dangerous (object resurrection) and should be avoided class Test { ~Test() { ... finalization work ... // automatically calls the destructor of the base class } }
  15. 15. Inheritance
  16. 16. Constructors and Inheritance
  17. 17. using System; public class ParentClass { public ParentClass() { Console.WriteLine("Parent Constructor."); } public void print() { Console.WriteLine("I'm a Parent Class."); } } public class ChildClass : ParentClass { public ChildClass() { Console.WriteLine("Child Constructor."); } public static void Main() { ChildClass child = new ChildClass(); child.print(); } } Inheritance
  18. 18. using System; public class ParentClass { public ParentClass() { Console.WriteLine("Parent Constructor."); } public void print() { Console.WriteLine("I'm a Parent Class."); } } public class ChildClass : ParentClass { public ChildClass() { Console.WriteLine("Child Constructor."); } public static void Main() { ChildClass child = new ChildClass(); child.print(); } } Inheritance
  19. 19. using System; public class ParentClass { public ParentClass() { Console.WriteLine("Parent Constructor."); } public void print() { Console.WriteLine("I'm a Parent Class."); } } public class ChildClass : ParentClass { public ChildClass() { Console.WriteLine("Child Constructor."); } public static void Main() { ChildClass child = new ChildClass(); child.print(); } } Inheritance
  20. 20. using System; public class ParentClass { public ParentClass() { Console.WriteLine("Parent Constructor."); } public void print() { Console.WriteLine("I'm a Parent Class."); } } public class ChildClass : ParentClass { public ChildClass() { Console.WriteLine("Child Constructor."); } public static void Main() { ChildClass child = new ChildClass(); child.print(); } } Parent Constructor. Child Constructor. I'm a Parent Class. Inheritance
  21. 21. public class Parent { string parentString; public Parent() { Console.WriteLine("Parent Constructor."); } public Parent(string myString) { parentString = myString; Console.WriteLine(parentString); } public void print() { Console.WriteLine("I'm a Parent Class."); } } public class Child : Parent { public Child() : base("From Derived") { Console.WriteLine("Child Constructor."); } public new void print() { base.print(); Console.WriteLine("I'm a Child Class."); } public static void Main() { Child child = new Child(); child.print(); ((Parent)child).print(); } } Inheritance
  22. 22. public class Parent { string parentString; public Parent() { Console.WriteLine("Parent Constructor."); } public Parent(string myString) { parentString = myString; Console.WriteLine(parentString); } public void print() { Console.WriteLine("I'm a Parent Class."); } } public class Child : Parent { public Child() : base("From Derived") { Console.WriteLine("Child Constructor."); } public new void print() { base.print(); Console.WriteLine("I'm a Child Class."); } public static void Main() { Child child = new Child(); child.print(); ((Parent)child).print(); } } Inheritance
  23. 23. public class Parent { string parentString; public Parent() { Console.WriteLine("Parent Constructor."); } public Parent(string myString) { parentString = myString; Console.WriteLine(parentString); } public void print() { Console.WriteLine("I'm a Parent Class."); } } public class Child : Parent { public Child() : base("From Derived") { Console.WriteLine("Child Constructor."); } public new void print() { base.print(); Console.WriteLine("I'm a Child Class."); } public static void Main() { Child child = new Child(); child.print(); ((Parent)child).print(); } } From Derived Child Constructor. I'm a Parent Class. I'm a Child Class. I'm a Parent Class. Inheritance
  24. 24. Polymorphism
  25. 25. public class DrawingObject { public virtual void Draw() { Console.WriteLine( "I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } public class Circle : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Circle."); } } public class Square : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Square."); } } Polymorphism
  26. 26. public class DrawingObject { public virtual void Draw() { Console.WriteLine( "I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } public class Circle : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Circle."); } } public class Square : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Square."); } } Polymorphism
  27. 27. public class DrawingObject { public virtual void Draw() { Console.WriteLine( "I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } public class Circle : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Circle."); } } public class Square : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Square."); } } Polymorphism
  28. 28. class Program { static void Main(string[] args) { DrawingObject[] dObj = new DrawingObject[4]; dObj[0] = new Line(); dObj[1] = new Circle(); dObj[2] = new Square(); dObj[3] = new DrawingObject(); foreach (DrawingObject drawObj in dObj) { drawObj.Draw(); } } } Polymorphism
  29. 29. class Program { static void Main(string[] args) { DrawingObject[] dObj = new DrawingObject[4]; dObj[0] = new Line(); dObj[1] = new Circle(); dObj[2] = new Square(); dObj[3] = new DrawingObject(); foreach (DrawingObject drawObj in dObj) { drawObj.Draw(); } } } I'm a Line. I'm a Circle. I'm a Square. I'm just a generic drawing object. Press any key to continue... Polymorphism
  30. 30. public class DrawingObject { public DrawingObject(string objectName) { } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  31. 31. public class DrawingObject { public DrawingObject(string objectName) { } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  32. 32. public class DrawingObject { public DrawingObject(string objectName) { } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  33. 33. public class DrawingObject { public DrawingObject(string objectName) { } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  34. 34. public class DrawingObject { public DrawingObject(string objectName) { } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  35. 35. Polymorphism
  36. 36. Polymorphism
  37. 37. Polymorphism
  38. 38. public class DrawingObject { public DrawingObject(string objectName) { Console.WriteLine(objectName); } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public Line():base("ForBaseClass, DrawingObject") { Console.WriteLine(this.ToString()); } public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  39. 39. public class DrawingObject { public DrawingObject(string objectName) { Console.WriteLine(objectName); } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public Line():base("ForBaseClass, DrawingObject") { Console.WriteLine(this.ToString()); } public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  40. 40. public class DrawingObject { public DrawingObject(string objectName) { Console.WriteLine(objectName); } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public Line():base("ForBaseClass, DrawingObject") { Console.WriteLine(this.ToString()); } public override void Draw() { Console.WriteLine("I'm a Line."); } } ForBaseClass, DrawingObject ConsoleApplicationCourseTest.Line Press any key to continue... Polymorphism
  41. 41. public class DrawingObject { public DrawingObject(string objectName) { Console.WriteLine(objectName); } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public Line():base("ForBaseClass, DrawingObject") { Console.WriteLine(this.ToString()); } public override void Draw() { Console.WriteLine("I'm a Line."); } } ForBaseClass, DrawingObject ConsoleApplicationCourseTest.Line Press any key to continue... Polymorphism
  42. 42. public class DrawingObject { public DrawingObject(string objectName) { Console.WriteLine(objectName); } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public Line():base("ForBaseClass, DrawingObject") { Console.WriteLine(this.ToString()); } public override void Draw() { Console.WriteLine("I'm a Line."); } } ForBaseClass, DrawingObject ConsoleApplicationCourseTest.Line Press any key to continue... Polymorphism
  43. 43. Polymorphism
  44. 44. Polymorphism
  45. 45. public class DrawingObject { public DrawingObject(string objectName) { Console.WriteLine(objectName); } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public Line():base("ForBaseClass, DrawingObject") { Console.WriteLine(this.ToString()); } public override string ToString() { return "just another Line object on runtime!"; } public override void Draw() { Console.WriteLine("I'm a Line."); } } Polymorphism
  46. 46. public class DrawingObject { public DrawingObject(string objectName) { Console.WriteLine(objectName); } public virtual void Draw() { Console.WriteLine("I'm just a generic drawing object."); } } public class Line : DrawingObject { public Line():base("ForBaseClass, DrawingObject") { Console.WriteLine(this.ToString()); } public override string ToString() { return "just another Line object on runtime!"; } public override void Draw() { Console.WriteLine("I'm a Line."); } } ForBaseClass, DrawingObject just another Line object on runtime! Press any key to continue... Polymorphism
  47. 47. Abstract Classes
  48. 48. Abstract Classes • Abstract methods do not have an implementation. • Abstract methods are implicitly virtual. • If a class has abstract methods it must be declared abstract itself. • One cannot create objects of an abstract class. abstract class Stream { public abstract void Write(char ch); public void WriteString(string s) { foreach (char ch in s) Write(s); } } class File: Stream { public override void Write(char ch) {... write ch to disk...} }
  49. 49. sealed and internal classes sealed: can’t be extended (Java’s final) internal: can’t be used in other namespaces
  50. 50. Versioning
  51. 51. class DerivedClass: BaseClass { public override string Meth1() { return "MyDerived-Meth1"; } public new string Meth2() { return "MyDerived-Meth2"; } public string Meth3() { return "MyDerived-Meth3"; } public static void Main() { DerivedClassmD = new MyDerived(); BaseClass mB = (BaseClass)mD; System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3()); } } Versioning public class BaseClass { public virtual string Meth1() { return "BaseClass-Meth1"; } public virtual string Meth2() { return "BaseClass-Meth2"; } public virtual string Meth3() { return "BaseClass-Meth3"; } }
  52. 52. class DerivedClass: BaseClass { public override string Meth1() { return "MyDerived-Meth1"; } public new string Meth2() { return "MyDerived-Meth2"; } public string Meth3() { return "MyDerived-Meth3"; } public static void Main() { DerivedClassmD = new MyDerived(); BaseClass mB = (BaseClass)mD; System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3()); } } Versioning Overrides the virtual method Meth1 using the override keyword public class BaseClass { public virtual string Meth1() { return "BaseClass-Meth1"; } public virtual string Meth2() { return "BaseClass-Meth2"; } public virtual string Meth3() { return "BaseClass-Meth3"; } }
  53. 53. class DerivedClass: BaseClass { public override string Meth1() { return "MyDerived-Meth1"; } public new string Meth2() { return "MyDerived-Meth2"; } public string Meth3() { return "MyDerived-Meth3"; } public static void Main() { DerivedClassmD = new MyDerived(); BaseClass mB = (BaseClass)mD; System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3()); } } Versioning Explicitly hide the virtual method Meth2 using the new keyword public class BaseClass { public virtual string Meth1() { return "BaseClass-Meth1"; } public virtual string Meth2() { return "BaseClass-Meth2"; } public virtual string Meth3() { return "BaseClass-Meth3"; } }
  54. 54. class DerivedClass: BaseClass { public override string Meth1() { return "MyDerived-Meth1"; } public new string Meth2() { return "MyDerived-Meth2"; } public string Meth3() { return "MyDerived-Meth3"; } public static void Main() { DerivedClassmD = new MyDerived(); BaseClass mB = (BaseClass)mD; System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3()); } } Versioning Because no keyword is specified in the following declaration a warning will be issued to alert the programmer that the method hides the inherited member BaseClass.Meth3() public class BaseClass { public virtual string Meth1() { return "BaseClass-Meth1"; } public virtual string Meth2() { return "BaseClass-Meth2"; } public virtual string Meth3() { return "BaseClass-Meth3"; } }
  55. 55. class DerivedClass: BaseClass { public override string Meth1() { return "MyDerived-Meth1"; } public new string Meth2() { return "MyDerived-Meth2"; } public string Meth3() { return "MyDerived-Meth3"; } public static void Main() { DerivedClassmD = new MyDerived(); BaseClass mB = (BaseClass)mD; System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3()); } } Versioning public class BaseClass { public virtual string Meth1() { return "BaseClass-Meth1"; } public virtual string Meth2() { return "BaseClass-Meth2"; } public virtual string Meth3() { return "BaseClass-Meth3"; } } MyDerived-Meth1 BaseClass-Meth2 BaseClass-Meth3
  56. 56. Multiple Inheritance? C#.NET doesn't allow it, Why?
  57. 57. Multiple Inheritance? C#.NET doesn't allow it C++.NET doesn’t allow it Java doesn’t allow it C++, as you know, allows it
  58. 58. However, C# allow multiple interfaces
  59. 59. However, C# allow multiple interfaces But what are they?
  60. 60. Interfaces
  61. 61. Interfaces :D
  62. 62. Interfaces – The concept
  63. 63. Interfaces VS Abstract Classes
  64. 64. Interfaces • An interface contains only the signatures of methods, delegates or events. • The implementation of the methods is done in the class that implements the interface. • Can’t contain Fields!
  65. 65. When to use? (An Example)
  66. 66. Consider a Human, an Animal and a Car Class, where they all implement a crazy method called ConsumeWater(). If we have many objects of each type of Human, Animal and Car and we want to call ConsumeWater() for all objects of Human, Animal and Car; we have to call it like this: human1.ConsumeWater(); human2.ConsumeWater(); human3.ConsumeWater(); animal1.ConsumeWater(); animal2.ConsumeWater(); car1.ConsumeWater(); car2.ConsumeWater();
  67. 67. SomeObject Human Animal Car And they they can’t be subclassed from one particular abstract/base class like this:
  68. 68. SomeObject Human Animal Car And they they can’t be subclassed from one particular abstract/base class like this: Because they are not the same and they share some common properties!
  69. 69. If we have many objects of each type of Human, Animal and Car and we want to call ConsumeWater() for all objects of Human, Animal and Car; we have to call it like this: human1.ConsumeWater(); human2.ConsumeWater(); human3.ConsumeWater(); animal1.ConsumeWater(); animal2.ConsumeWater(); car1.ConsumeWater(); car2.ConsumeWater(); But if we can implement a common functionalities from a common place, that would be nice! interface Human Animal Car Implementation and not inheritance!
  70. 70. If we have many objects of each type of Human, Animal and Car and we want to call ConsumeWater() for all objects of Human, Animal and Car; we have to call it like this: human1.ConsumeWater(); human2.ConsumeWater(); human3.ConsumeWater(); animal1.ConsumeWater(); animal2.ConsumeWater(); car1.ConsumeWater(); car2.ConsumeWater(); But if we can implement a common functionalities from a common place, that would be nice! IWaterable Human Animal Car Implementation and not inheritance!
  71. 71. Now we can add all objects to a common list of IWaterable and just call ConsumeWater() for each IWaterable object (they are all Waterable now!) List<IWaterable> waterables = new List<IWaterable>() {“human1”, “human2”, “human3”, “animal1”, “animal2”, “car1”, “car2”}; foreach(IWaterable waterable in waterables) waterable.ConsumeWater(); Look how nice the code is and how clear the relation is. When we implement an interface we are just saying that this interface provides a certain functionality for us (and others may freely have this functionality as well.) IWaterable Human Animal Car Implementation and not inheritance!
  72. 72. Interfaces – the Code
  73. 73. Interfaces – the Code Public interface IWaterable { public void ConsumeWater(); }
  74. 74. Interfaces – the Code Public interface IWaterable { public void ConsumeWater(); } Public class Human: IWaterable { public void ConsumeWater() { } } Public class Animal: IWaterable { public void ConsumeWater() { } } Public class Car: IWaterable { public void ConsumeWater() { } }
  75. 75. Interfaces – the Code Public interface IWaterable { public void ConsumeWater(); } Public class Human: IWaterable { public void ConsumeWater() { } } Public class Animal: IWaterable { public void ConsumeWater() { } } Public class Car: IWaterable { public void ConsumeWater() { } }
  76. 76. Interfaces – the Code Public interface IWaterable { public void ConsumeWater(); } Public class Human: IWaterable { public void ConsumeWater() { //Drinking Water } } Public class Animal: IWaterable { public void ConsumeWater() { //Drinking Water } } Public class Car: IWaterable { public void ConsumeWater() { //Cooling the engine } }
  77. 77. Interfaces – the Code Public interface IWaterable { public void ConsumeWater(); } Public class Human: IWaterable { public void ConsumeWater() { //Drinking Water } } Public class Animal:IWaterable, INosiable { public void ConsumeWater() { //Drinking Water } public void MakeNoise() { //Mew, Roar or Moo! } } Public class Car: IWaterable, INosiable { public void ConsumeWater() { //Cooling the engine } public void MakeNoise() { //Rev the engine! } } Public interface INoisable { public void MakeNoise(); }
  78. 78. Interfaces • An interface can be a member of a namespace or a class and can contain signatures of the following members: – Methods – Properties – Indexers – Events • “No” Fields!
  79. 79. Reference VS Value Types
  80. 80. using System; class Program { static void Main() { float lengthFloat = 7.35f; // lose precision - explicit conversion int lengthInt = (int)lengthFloat; // no problem - implicit conversion double lengthDouble = lengthInt; Console.WriteLine("lengthInt = " + lengthInt); Console.WriteLine("lengthDouble = " + lengthDouble); Console.ReadKey(); } } Reference VS Value Types
  81. 81. using System; class Program { static void Main() { float lengthFloat = 7.35f; // lose precision - explicit conversion int lengthInt = (int)lengthFloat; // no problem - implicit conversion double lengthDouble = lengthInt; Console.WriteLine("lengthInt = " + lengthInt); Console.WriteLine("lengthDouble = " + lengthDouble); Console.ReadKey(); } } lengthInt = 7 lengthDouble = 7 Reference VS Value Types
  82. 82. Reference VS Value Types • Reference type • variables are named appropriately (reference) because the variable holds a reference to an object. • In C and C++, we have something similar that which is “a pointer”, which points to an object. While you can modify a pointer, you can't modify the value of a reference - it simply points at the object in memory.
  83. 83. using System; class Employee { private string _name; public string Name { get { return _name; } set { _name = value; } } } Reference VS Value Types
  84. 84. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } }
  85. 85. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Original Employee Values: joe = Joe bob = Bob Values After Reference Assignment: joe = Joe bob = Joe Values After Changing One Instance: joe = Bobbi Jo bob = Bobbi Jo
  86. 86. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Original Employee Values: joe = Joe bob = Bob Values After Reference Assignment: joe = Joe bob = Joe Values After Changing One Instance: joe = Bobbi Jo bob = Bobbi Jo How is that?!
  87. 87. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp Emp joe bob
  88. 88. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp Emp joe bob
  89. 89. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp Emp joe bob
  90. 90. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp Emp joe bob
  91. 91. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp Emp joe bob
  92. 92. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp joe Emp bob
  93. 93. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp joe Emp bob
  94. 94. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp joe Emp bob
  95. 95. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } Emp joe bob
  96. 96. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } joe bob Emp Name = “Joe”
  97. 97. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } joe bob Emp Name = “Bobbi Jo”
  98. 98. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } joe bob Emp Name = “Bobbi Jo”
  99. 99. Reference Types class Program { static void Main() { Employee joe = new Employee(); joe.Name = "Joe"; Employee bob = new Employee(); bob.Name = "Bob"; Console.WriteLine("Original Employee Values:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); // assign joe reference to bob variable bob = joe; Console.WriteLine("Values After Reference Assignment:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); joe.Name = "Bobbi Jo"; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Name); Console.WriteLine("bob = " + bob.Name); Console.ReadKey(); } } joe bob Emp Name = “Bobbi Jo” Original Employee Values: joe = Joe bob = Bob Values After Reference Assignment: joe = Joe bob = Joe Values After Changing One Instance: joe = Bobbi Jo bob = Bobbi Jo
  100. 100. Reference Types • The following types are reference types: • arrays • class • delegates • interfaces
  101. 101. Value Types
  102. 102. Value Types • A value type – variable holds its own copy of an object and when you perform assignment from one value type variable to another, both the left-hand-side and right-hand-side of the assignment hold two separate copies of that value.
  103. 103. Value Types • A value type – variable holds its own copy of an object and when you perform assignment from one value type variable to another, both the left-hand-side and right-hand-side of the assignment hold two separate copies of that value. • An important fact you need to understand is that when you are assigning one reference type variable to another, only the reference is copied, not the object. The variable holds the reference and that is what is being copied.
  104. 104. struct Height { private int m_inches; public int Inches { get { return m_inches; } set { m_inches = value; } } } Value Types
  105. 105. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types
  106. 106. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types Height Height joe bob
  107. 107. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types Height Height joe bob
  108. 108. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types Height Height joe bob Height
  109. 109. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types Height Height joe bob Exactly the same
  110. 110. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types 71 71 joe bob Exactly the same
  111. 111. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types 71 71 joe bob
  112. 112. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types 65 71 joe bob
  113. 113. class Program { static void Main() { Height joe = new Height(); joe.Inches = 71; Height bob = new Height(); bob.Inches = 59; Console.WriteLine("Original Height Values:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); bob = joe; Console.WriteLine("Values After Value Assignment:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); joe.Inches = 65; Console.WriteLine("Values After Changing One Instance:"); Console.WriteLine("joe = " + joe.Inches); Console.WriteLine("bob = " + bob.Inches); Console.ReadKey(); } } Value Types 65 71 joe bob Original Height Values: joe = 71 bob = 59 Values After Value Assignment: joe = 71 bob = 71 Values After Changing One Instance: joe = 65 bob = 71
  114. 114. Value Types • The following types are value types: – enum – struct
  115. 115. Classes and Structs Classes • Reference Types • (objects stored on the heap) • support inheritance • (all classes are derived from object) • can implement interfaces • may have a destructor Structs • Value Types • (objects stored on the stack) • no inheritance • (but compatible with object) • can implement interfaces • no destructors allowed
  116. 116. Creating a Class Library Project for Your Project’s Logic
  117. 117. Now write all your code in the Class Library project and reference it in your presentation layer project
  118. 118. Adding References to Other Projects to Your Project
  119. 119. Adding References to Your Project
  120. 120. The Principles • Single Responsibility Principle: design your classes so that each has a single purpose • Open / Closed Principle: Open for extension but closed for modification • Liskov Substitution Principle (LSP): functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it • Interface Segregation Principle (ISP): clients should not be forced to depend upon interfaces that they do not use. • Dependency Inversion Principle (DIP): high level modules should not depend upon low level modules. Both should depend upon abstractions. abstractions should not depend upon details. Details should depend upon abstractions.
  121. 121. is the process of validating the correctness of a small section of code. The target code may be a method within a class, a group of members or even entire components that are isolated from all or most of their dependencies.
  122. 122. Question #1 public class BaseClass { public virtual string Meth1() { return "BaseClass-Meth1"; } public string Meth2() { return "BaseClass-Meth2"; } public virtual string Meth3() { return "BaseClass-Meth3"; } } class DerivedClass: BaseClass { public override string Meth1() { return "MyDerived-Meth1"; } public new string Meth2() { return "MyDerived-Meth2"; } public string Meth3() { return "MyDerived-Meth3"; } public static void Main() { DerivedClassmD = new MyDerived(); BaseClass mB = mD; System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3()); } }
  123. 123. Question #1 public class BaseClass { public virtual string Meth1() { return "BaseClass-Meth1"; } public string Meth2() { return "BaseClass-Meth2"; } public virtual string Meth3() { return "BaseClass-Meth3"; } } class DerivedClass: BaseClass { public override string Meth1() { return "MyDerived-Meth1"; } public new string Meth2() { return "MyDerived-Meth2"; } public string Meth3() { return "MyDerived-Meth3"; } public static void Main() { DerivedClassmD = new MyDerived(); BaseClass mB = mD; System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3()); } } MyDerived-Meth1 BaseClass-Meth2 BaseClass-Meth3 Press any key to continue...
  124. 124. Question #2 class Class1 { } class Class2 : Class1{ } class Class3 { } public class TestingClass { public static void Test(object o) { Class1 a; Class2 b; Class3 c; if (o is Class1) { Console.WriteLine("obj is Class1"); a = (Class1)o; } else if (o is Class2) { Console.WriteLine("obj is Class2"); b = (Class2)o; } else if (o is Class3) { Console.WriteLine("obj is Class3"); c = (Class3)o; } else if((Class3)o!= null) {} } public static void Main() { try { Class1 c1 = new Class1(); Class2 c2 = new Class2(); Class3 c3 = new Class3(); Test(c1); Test(c2); Test(c3); Test("a string"); } catch(Exception e) { Console.WriteLine("Sth wrong happened!"); } } }
  125. 125. Question #2 class Class1 { } class Class2 : Class1{ } class Class3 { } public class TestingClass { public static void Test(object o) { Class1 a; Class2 b; Class3 c; if (o is Class1) { Console.WriteLine("obj is Class1"); a = (Class1)o; } else if (o is Class2) { Console.WriteLine("obj is Class2"); b = (Class2)o; } else if (o is Class3) { Console.WriteLine("obj is Class3"); c = (Class3)o; } else if((Class3)o!= null) {} } public static void Main() { try { Class1 c1 = new Class1(); Class2 c2 = new Class2(); Class3 c3 = new Class3(); Test(c1); Test(c2); Test(c3); Test("a string"); } catch(Exception e) { Console.WriteLine("Sth wrong happened!"); } } } obj is Class1 obj is Class1 obj is Class3 Sth wrong happened! Press any key to continue...
  126. 126. public interface IsBaseTest { void Point1(object obj); } public class IsTest { public static void Point1(object obj) { Console.WriteLine(obj.ToString()); Point2("That's the point"); } public static void Point2(string str) { Console.WriteLine(str.ToString()); Point3("That's the point"); } public static void Point3(object obj) { if (obj.ToString() == " Passed String") { Console.WriteLine("In Point3"); } } public static void Main() { Point1("Passed String"); } } Question #3
  127. 127. public interface IsBaseTest { void Point1(object obj); } public class IsTest { public static void Point1(object obj) { Console.WriteLine(obj.ToString()); Point2("That's the point"); } public static void Point2(string str) { Console.WriteLine(str.ToString()); Point3("That's the point"); } public static void Point3(object obj) { if (obj.ToString() == " Passed String") { Console.WriteLine("In Point3"); } } public static void Main() { Point1("Passed String"); } } Question #3 Passed String That's the point In Point3 Press any key to continue...
  128. 128. That’s it for today! Hope you enjoy it!

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