c# starter l02-classes and objects
TRANSCRIPT
Mohammad Shakermohammadshaker.com
C# Programming Course@ZGTRShaker
2011, 2012, 2013, 2014
C# StarterL02 – Classes, Polymorphism, Versioning, Interfaces, Reference and Value Types
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 objects.
Classes
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;
}}
Classes and ObjectsWho is Who?
Objects appear only at Runtime
this Keyword
this KeywordWhat is it?
this KeywordA 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 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;
}
Static KeywordWhat is it?
Destructors
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
}}
Inheritance
Constructors and Inheritance
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
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
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
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
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
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
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 DerivedChild Constructor.I'm a Parent Class.I'm a Child Class.I'm a Parent Class.
Inheritance
Polymorphism
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
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
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
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
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
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
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
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
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
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
Polymorphism
Polymorphism
Polymorphism
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
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
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, DrawingObjectConsoleApplicationCourseTest.LinePress any key to continue...
Polymorphism
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, DrawingObjectConsoleApplicationCourseTest.LinePress any key to continue...
Polymorphism
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, DrawingObjectConsoleApplicationCourseTest.LinePress any key to continue...
Polymorphism
Polymorphism
Polymorphism
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
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, DrawingObjectjust another Line object on runtime!Press any key to continue...
Polymorphism
Abstract Classes
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...}}
sealed and internal classessealed: 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(){
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";}
}
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";}
}
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";}
}
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";}
}
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-Meth1BaseClass-Meth2BaseClass-Meth3
Multiple Inheritance?C#.NET doesn't allow it, Why?
Multiple Inheritance?C#.NET doesn't allow it
C++.NET doesn’t allow itJava doesn’t allow it
C++, as you know, allows it
However, C# allow multiple interfaces
However, C# allow multiple interfacesBut 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 methods is done in the class that implements the
interface.
• Can’t contain Fields!
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 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();
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 they are not the same and they share some common properties!
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!
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!
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!
Interfaces – the Code
Interfaces – the CodePublic interface IWaterable{
public void ConsumeWater();}
Interfaces – the CodePublic 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(){
} }
Interfaces – the CodePublic 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(){
} }
Interfaces – the CodePublic 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}
}
Interfaces – the CodePublic 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();}
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!
Reference VS Value Types
using System;
class Program{
static void Main(){
float lengthFloat = 7.35f;
// lose precision - explicit conversionint lengthInt = (int)lengthFloat;
// no problem - implicit conversiondouble lengthDouble = lengthInt;
Console.WriteLine("lengthInt = " + lengthInt);Console.WriteLine("lengthDouble = " + lengthDouble);Console.ReadKey();
}}
Reference VS Value Types
using System;
class Program{
static void Main(){
float lengthFloat = 7.35f;
// lose precision - explicit conversionint lengthInt = (int)lengthFloat;
// no problem - implicit conversiondouble lengthDouble = lengthInt;
Console.WriteLine("lengthInt = " + lengthInt);Console.WriteLine("lengthDouble = " + lengthDouble);Console.ReadKey();
}}
lengthInt = 7lengthDouble = 7
Reference VS Value Types
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.
using System;
class Employee{
private string _name;
public string Name{
get { return _name; }set { _name = value; }
}}
Reference VS Value Types
Reference Typesclass 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 variablebob = 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();}
}
Reference Typesclass 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 variablebob = 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 = Joebob = BobValues After Reference Assignment:joe = Joebob = JoeValues After Changing One Instance:joe = Bobbi Jobob = Bobbi Jo
Reference Typesclass 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 variablebob = 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 = Joebob = BobValues After Reference Assignment:joe = Joebob = JoeValues After Changing One Instance:joe = Bobbi Jobob = Bobbi Jo
How is that?!
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
Reference Typesclass 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 variablebob = 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
EmpName = “Joe”
Reference Typesclass 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 variablebob = 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
EmpName =
“Bobbi Jo”
Reference Typesclass 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 variablebob = 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
EmpName =
“Bobbi Jo”
Reference Typesclass 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 variablebob = 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
EmpName =
“Bobbi Jo”
Original Employee Values:joe = Joebob = BobValues After Reference Assignment:joe = Joebob = JoeValues After Changing One Instance:joe = Bobbi Jobob = Bobbi Jo
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 variable to another, both the left-hand-side and right-hand-side of the assignment hold
two separate copies of that value.
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.
struct Height{
private int m_inches;
public int Inches{
get { return m_inches; }set { m_inches = value; }
}}
Value Types
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
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 TypesHeight Height
joe bob
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 TypesHeight Height
joe bob
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 TypesHeight Height
joe bob
Height
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 TypesHeight Height
joe bob
Exactly the
same
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 Types71 71
joe bob
Exactly the
same
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 Types71 71
joe bob
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 Types65 71
joe bob
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 Types65 71
joe bob
Original Height Values:joe = 71bob = 59Values After Value Assignment:joe = 71bob = 71Values After Changing One Instance:joe = 65bob = 71
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 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
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 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.
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.
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());
}}
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-Meth1BaseClass-Meth2BaseClass-Meth3Press any key to continue...
Question #2class 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!");}
}}
Question #2class 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 Class1obj is Class1obj is Class3Sth wrong happened!Press any key to continue...
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
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 StringThat's the pointIn Point3Press any key to continue...
That’s it for today!Hope you enjoy it!