Abstract
and Virtual:
•If a class is to serve the purpose of
providing common fields and members to all subclasses, we create an Abstract
class. For creating an abstract class, we make use of the abstract keyword.
Such a class cannot be instantiated.
•Whatever functionality in common to the
entire system which functionality put together and keep into separate.
Why do
we need Abstract class:
•Take three classes Human, Man and Woman. All
Man and Woman belong to Human category. In Original
object exists for only for Man or Woman. NO object exists for Human category. But both Man and Woman have
common characteristics where we can say it as Human characters. Now you can understand that why
do we need abstract class.
Abstract
Rules
-> We cannot create object for abstract
class
-> we cannot declare the abstract method
in non abstract class
-> we cannot declare the non abstract
method or virtual method without declare the body
-> We cannot declare a body in abstract
method
-> When at least one of the methods in the
class is abstract.
-> Abstract
can extend only one abstract class.
->An
abstract class can extend c# class only
Difference
between Abstract and Virtual
Abstract
|
Virtual
|
No
Keyword
|
|||||||||||||
Can have
implementation?
|
No
|
Yes
|
Yes
|
||||||||||||
Can override?
|
Must
|
Can but not a must
|
You can declare a new
method with the same name
|
||||||||||||
Which keyword to use to
provide new implementation in the concrete class?
|
override
|
override
|
No keyword needed
|
||||||||||||
Concrete implementation
|
The parent
implementation will be called only if no implementation is provided in the
concrete class
|
Parent implementation
|
|||||||||||||
Concrete implementation
|
Concrete implementation
|
The parent
implementation will be called only if no implementation is provided in the
concrete class
|
|||||||||||||
Interface
•Interface nothing but skeleton of the class
•We cant create object for interface
•It s a Pure abstraction
•Pure abstraction means you cannot have
concrete methods
•Interfaces should not have any concrete
methods, it should only have method declarations.
A method with definition is concrete method
In which
scenario we use Interfaces:
•If your child classes should all implement a
certain group of methods/functionalities but each of the child classes is free
to provide its own implementation then use interfaces.
•For e.g. if you are implementing a class
hierarchy for vehicles implement an interface called Vehicle which has
properties like Color MaxSpeed etc. and methods like Drive(). All child
classes like Car Scooter Airplane Solar Car etc. should derive from this base
interface but provide a separate implementation of the methods and properties
exposed by Vehicle
Which one is advantage over another:
•Interface has advantage over Abstract class.
Since you can not use abstract class for already inherited class. But you can
use interface for already inherited class.
Difference
between Abstract and Interface:
•We declared 10 methods in interface, now we
should implement all 10 methods. But we want implement 2 methods only.
•How?
•Example.
Sealed
Class:
•Sealed classes are used to restrict the
inheritance feature of object oriented programming
•A sealed class cannot be used as a base
class.
•Sealing a class means one cannot derive
from it.
•A method means one cannot override it.
•Example.
Polymorphism
•Polymorphism means many forms.
•Polymorphism is the ability to process
objects differently depending on their data types.
•Polymorphism is the ability to redefine
methods for derived classes.
Polymorphism provides
following features:
•It allows you to invoke methods of derived
class through base class reference during runtime.
•It has the ability for classes to provide
different implementations of methods that are called through the same name.
Polymorphism
Polymorphism is of two
types:
1.Compile time polymorphism/Overloading
2.Runtime polymorphism/Overriding
Compile Time Polymorphism
• Compile time polymorphism is method
overloading. It is also called early binding.
• In method overloading method performs
the different task at the different input parameters.
Runtime Time Polymorphism
• Runtime time polymorphism is done using
inheritance and virtual functions. Method overriding is called runtime
polymorphism. It is also called late binding
Overloading:
•Overloading a method simply involves
having another method with the same prototype.
Overriding
•To change the behavior of the method for the
derived class
Note
•Method overloading has nothing to do with
inheritance or virtual methods.
Following are examples of
methods having different overloads:
•void area(int side);
•void area(int l, int b);
•Void area(int l, double b, int c)
•Void area(double b, int l, int c)
•void area(float radius);
Polymorphism
When and why
to use method overloading
• Use method overloading in situation where
you want a class to be able to do something, but there is more than one
possibility for what information is supplied to the method that carries out the
task.
• You should consider overloading a method
when you for some reason need a couple of methods that take different
parameters, but conceptually do the same thing.
•Example
•
• Void Area(int a)
//Square
•Void Area(int h,int w)
//Rectangle
•Void Area(int a, int l, int w)
//Cylinder
•Void Area(int pi, int r ,
int
l) //Cone
•Void Area(int pi, int r
) //Circle
When and why
to use method overriding
•Its obvious that when we do inheritance
between two classes, all the methods and properties of the first class are
derived to the other class so that this becomes the child class which
adobes all the functionality of base class. It can also possesses its own
separate methods.
•But there is a big problem in inheriting the
second class to the first class as it adobes all the methods same as the base
class has, which means that after inheritance both(base class& child
class) have the methods of same name and same body as shown in this example
•Example,
we
have seen example of overriding
•how many overload of a method we can have?
•
•What?
•Type?
•When?
•Overloading?
•Overriding?
•static binding?
•Late binding?
String
and String Builder:
•Strings are Immutable
(Not Modifiable). If you try to modify the string it actually creates a new
string and the old string will be then ready for garbage collection.
•String Builder when instantiated, creates a
new string with predefined capacity and up to that capacity it can accommodate
string without needing to create a new memory location for the string....i
mean it is modifiable and can also grow as and when needed.
•The most common operation with a string is
concatenation. This activity has to be performed very efficiently. When we use
the "String" object to concatenate two strings, the first string is
combined to the other string by creating a, and then the old string is deleted.
This process is a little long. Hence we say "Strings are immutable".
•When we make use of the "String
Builder" object, the Append method is used. This means, an insertion is
done on the existing string. Operation on String Builder object is faster than
String operations, as the copy is done to the same location. Usage of String
Builder is more efficient incase large amounts of string manipulations have to
be performed.
•String Example:
String
myString=”Welcome”;
myString=myString+”Software
Team”;
•String builder Example
StringBuilder sb =
new StringBuilder();
sb.Append("raj");
sb.Append("mani");
String
builder
Methods:
Ex:
Append, insert, remove, replace and Tostring.
Performance:
1.Avoid short appends.
2.Cache objects.
3.Avoid some data types.
4.Data Types
5.Append Chars
6.Stringbuilder Comparison
7.Append integers
8.Capacity
●
9.Example:
http://www.dotnetperls.com/stringbuilder
Override: When a method of a base class is overridden in a derived class, the version in the derived class is used, even if the calling code didn't "know" that the object was an instance of the derived class.
New: If you use the new keyword instead of override, the method in the derived class doesn't override the method in the base class, it merely hides it.
If you don't specify either new or overrides, the resulting output is the same as if you specified new, but you'll also get a compiler warning (as you may not be aware that you're hiding a method in the base class method, or indeed you may have wanted to override it, and merely forgot to include the keyword).
Override: used with virtual/abstract/override type of method in base class
New: when base class has not declared method as virtual/abstract/override
Static
class , method and variables
12 Features of Static class
1.A static class cannot be instantiated
2.Static class can have only static members.
3.Member of the Static class can be accessed by
class name itself.
4.Static class is sealed. So static class
cannot be inherited.
5.Static class contains only static
constructors.
6.Static class cannot have instance
constructors.
7.Static class can only be inherited only from
object class.
8.Static class is preceded by keyword static.
9.Static constructor of static class called
only once.
10.Static class has private constructors
11.Static classes cannot implement interfaces
12.static classes cannot have instance
constructors
Notable Points here are:
•A static method can be invoked directly from
the class level
•A static method not requires any class object
•Any main() method is shared through entire
class scope so it always appears with static keyword.
Static method
•A static method can access only static
fields.
•A static method cannot access non static
fields.
•A static method cannot be called using object
of a class
•A static method can be called using class
name.
• Static field can be used using class name.
•Static method cannot be override or overload.
•We can't put access modifier in static
constructor?
Constructor:
http://www.programcall.com/16/csnet/constructor-types-with-example-programs-in-csnet.aspx
•A static constructor does not take access
modifiers or have parameters.
•A static constructor is called automatically
to initialize the class before the first instance is created or
any static members are referenced.
•A static constructor cannot be called
directly.
•The user has no control on when the static
constructor is executed in the program.
•A typical use of static constructors is when
the class is using a log file and the constructor is used to write entries to
this file.
•Static constructors are also useful when
creating wrapper classes for unmanaged code, when the constructor can call the LoadLibrary method.
•If a static constructor throws an exception,
the runtime will not invoke it a second time, and the type will remain
uninitialized for the lifetime of the application domain in which your program
is running.
http://msdn.microsoft.com/en-us/library/k9x6w0hc.aspx
what
is difference between instance constructor and Static constructor in C#.Net
Main Differences are :
• A Constructor declare using Static
modifier was known as Static Constructor. Rest of all were Instance
Constructor.
•Static Constructor are responsible for
initialization of static variables and Instance Constructor for initialization
of instance constructor.
•A static constructor is called only one's in
the execution of a class. Where as instance constructor gets called each time
we create the object of the class. if no object is created. It is not called at
all.
•static constructor is the first block of
which gets executed under the class.
•A static constructor can't be parameterized
because explicit calling of the constructor is not done.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1{
class staticconstructor
{
static staticconstructor()
{
Console.WriteLine("static constructor");
}
staticconstructor()
{
Console.WriteLine("non-static constructor");
}
static void
Main()
{
Console.WriteLine("main method");
staticconstructor st = new staticconstructor();
staticconstructor st1 = new staticconstructor();
Console.ReadLine();
}
}
}
o/p: static constructor, main method
, non-static constructor , non-static constructor
Notable Points here are:
•A static method can be invoked directly from
the class level
•A static method not requires any class object
•Any main() method is shared through entire
class scope so it always appears with static keyword.
Static method
•A static method can access only static
fields.
•A static method cannot access non static
fields.
•A static method cannot be called using object
of a class
•A static method can be called using class
name.
• Static field can be used using class name.
•Static method cannot be override.
•We can't put access modifier in static
constructor?
public static string GetData(int CustomerID) {
Page page
= HttpContext.Current.Handler as Page;
if (page != null)
{
string outputToReturn = "";
page.ViewState["MyVal"]="Hello";
return outputToReturn;
//btw,
what a strange method!
}
}
collection
Four important categories
•Index based
–Array
–List
•Key value pair
–Hash
table
–Sort
list
•Prioritized collection
–Queue
–Stack
•Specialized collection
–String
collection
–Hybrid
dictionary
array and array list
Hash
Table and Array List
hash table
HashTable:
HashTable stores a key-value pair type collection of
data.
NOTE:
Both key and value are object
the
key values are UNIQUE
Functions:
•Clear
•Remove
•Containskey
•Containsvalue
•Contains
•Add
Variables
•Count
Remove:
hash_table_name.Remove(key);
Remove All Values:
hash_table_name.Clear()
ContainsKey(Key)
its returns true or false..
ContainsValue(value):
its
returns true or false..
EXAMPLE
Hashtable sampleHt = New Hashtable sampleHt.add("US",”united States”) // Area- key. 1000 - value sampleHt.add("IND",”India”)
// To fetch the value we can use name, for example
String countryname=convert.tostring(sampleHt[“US”]);
sampleHt.remove(“US”);
IDictionaryEnumerator idic= sampleHt.GetEnumerator();
while(idic.MoveNext())
{
idic.Value.ToString();
}
|
Example
1:
// We
cannot crate object for abstract class
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public abstract
class AbstactClass
{
public abstract string
GetAbstractValue();
}
public class
main1
{
static void Main(string[]
args)
{
AbstactClass
absObj = new AbstactClass();
}
}
}
Error 1 Cannot
create an instance of the abstract class or interface 'ConsoleApplication1.AbstactClass'
Example 2:
// we
cannot declare the abstract method in non abstract class
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public class
AbstactClass
{
public abstract string
GetAbstractValue();
}
public class
main1
{
static void Main(string[]
args)
{
AbstactClass
absObj = new AbstactClass();
}
}
}
Error:
'ConsoleApplication1.AbstactClass.GetAbstractValue()'
is abstract but it is contained in non-abstract class
'ConsoleApplication1.AbstactClass'
Example 2:
// we
cannot declare the non abstract method without definition
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public abstract
class AbstactClass
{
public abstract void
GetAbstractValue();
public void
GetValue();
// public void
GetValue(); // don’t throw error
//{}
}
public class
Test : AbstactClass
{
public override void
GetAbstractValue()
{
}
}
public class
main1
{
static void Main(string[]
args)
{
Test
absObj = new Test();
absObj.GetAbstractValue();
}
}
}
// We
cannot declare a body in abstract method
public abstract class AbstactClass
{
public abstract void
GetAbstractValue()
{
}
public void GetValue()
{
Console.WriteLine("Get abstract method");
}
}
// Abstract,
virtual method
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public abstract
class BaseClass
{
public abstract string
GetAbstractValue();
public virtual string
GetVirtualValue()
{
return
"Base GetVirtualValue";
}
public string GetValue()
{
return
"Base GetValue";
}
}
public class
SubClass : BaseClass
{
public override string
GetAbstractValue()
{
return
"Sub Get Abstract Value";
}
public override string
GetVirtualValue()
{
return
"Sub GetVirtualValue";
}
public string GetValue() //new
{
return
"Concrete GetValue";
}
}
class Test
{
static void Main(string[]
args)
{
BaseClass
instance1 = new SubClass();
Console.WriteLine(instance1.GetAbstractValue());
Console.WriteLine(instance1.GetVirtualValue());
Console.WriteLine(instance1.GetValue());
SubClass
instance2 = new SubClass();
Console.WriteLine(instance2.GetAbstractValue());
Console.WriteLine(instance2.GetVirtualValue());
Console.WriteLine(instance2.GetValue());
Console.Read();
}
}
}
//Since you cannot use abstract class for already inherited class. But
you can use interface for already inherited class.
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public interface
inrefacename
{
void
somemethod();
}
public abstract
class BaseClass
{
public abstract string
GetAbstractValue();
public virtual string
GetVirtualValue()
{
return
"Base GetVirtualValue";
}
public string GetValue()
{
return
"Base GetValue";
}
}
public class
classtest
{
public string GetValue1()
{
return
"Base GetValue";
}
}
public class
classtest1 : classtest,
inrefacename
// baseclass – abstract class (will not use abstract class)
{
public string GetValue4()
{
return
"Base GetValue";
}
public void
somemethod()
{
Console.WriteLine("somemethod");
}
}
public class
SubClass : BaseClass
{
public override string
GetAbstractValue()
{
return
"Sub Get Abstract Value";
}
public override string
GetVirtualValue()
{
return
"Sub GetVirtualValue";
}
public string
GetValue() //new
{
return
"Concrete GetValue";
}
}
class Test
{
static void Main(string[]
args)
{
BaseClass
instance1 = new SubClass();
Console.WriteLine(instance1.GetAbstractValue());
Console.WriteLine(instance1.GetVirtualValue());
Console.WriteLine(instance1.GetValue());
SubClass
instance2 = new SubClass();
Console.WriteLine(instance2.GetAbstractValue());
Console.WriteLine(instance2.GetVirtualValue());
Console.WriteLine(instance2.GetValue());
Console.Read();
}
}
}
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public interface
IMyInterface
{
void
SomeMethod();
void
SomeOtherMethod();
}
public abstract
class MyClass
: IMyInterface
{
// Really
implementing this
public void SomeMethod()
{
// ...
}
// Derived
class must implement this
public abstract void
SomeOtherMethod();
}
class Test
{
static void Main(string[]
args)
{
Console.Read();
}
}
}
// Achieve multiple
inheritance concept via interface
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public interface
IA1
{
void
m2();
void
m();
}
public interface
IA2
{
void
m2();
}
public class
CA : IA1,
IA2
{
public void m()
{
}
public void m2()
{
Console.WriteLine("A");
}
}
public class
CA1 : CA
{
public void m()
{
}
public void m2()
{
Console.WriteLine("B");
}
}
public class
main1
{
static void Main(string[]
args)
{
CA
c1 = new CA();
c1.m();
c1.m2();
CA1
ca1 = new CA1();
ca1.m();
ca1.m2();
Console.Read();
}
}
}
// Dynamic Binding (hiding)
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class A
{
public virtual void
WhoAreYou() { Console.WriteLine("I am an A"); }
public virtual void
WhoAreYou1() { Console.WriteLine("I am an A1"); }
public virtual void
WhoAreYou2() { Console.WriteLine("I am an A2"); }
}
class B
: A
{
public override void
WhoAreYou() { Console.WriteLine("I am a B"); }
}
class C
: B
{
public new virtual void WhoAreYou() { Console.WriteLine("I am a C"); }
// public override void WhoAreYou1() {
Console.WriteLine("I am an C1"); }
public override void
WhoAreYou2() { Console.WriteLine("I am an C2"); }
}
class D
: C
{
public override void
WhoAreYou() { Console.WriteLine("I am a D"); }
public override void
WhoAreYou2() { Console.WriteLine("I am an D2"); }
}
class Test
{
static void Main(string[]
args)
{
C
c = new D(); // where to extend
C class in D
c.WhoAreYou();// "I am a D"
A
a = new D(); // where to
extend A class in B
a.WhoAreYou();// "I am a B"
A
a1 = new D(); // No extend -
virtual method
a1.WhoAreYou1(); // "I am a A1"
B a2 = new C(); // where to extend
b class in c
a2.WhoAreYou2(); // "I am a C2"
B
a3 = new D();
// where to extend b class in c
a3.WhoAreYou2(); // "I am a D2"
Console.ReadLine();
}
}
}
Sealed Class:
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public sealed
class classsealed
{
public string ID;
public double Price;
public string GetValue()
{
return
"Sealed class";
}
}
//public class subsealedclasss : classsealed
//{
//
public string subsealedmethod()
// {
//
return "subSealed class";
// }
//}
class Test
{
static void Main(string[]
args)
{
classsealed
sealedobject = new classsealed();
Console.WriteLine(sealedobject.GetValue());
sealedobject.ID = "10";
sealedobject.Price = 12.23;
//subsealedclassssubsealedobject
= new subsealedclasss();
//subsealedobject.subsealedmethod();
Console.Read();
}
}
}
// Static Class
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public static
class staticclass // : object //7. Static class can only be inherited only from
object class
{
// int a; //
2. Static class can have only static
members.
static int i=1; // access
//public void
method() // Static class can have only
static method.
//{
// Console.WriteLine("Test method");
//}
public static void method1()
{
Console.WriteLine("Test static method");
Console.WriteLine(i);
}
//staticclass() // static classess cannot have instance
constructors
//{
// Console.WriteLine("instance
constructor");
//}
static
staticclass()
{
Console.WriteLine("static constructor");
}
}
public class
Bus
{
// Static
constructor:
static
Bus()
{
System.Console.WriteLine("The static constructor invoked.");
}
public static void Drive()
{
System.Console.WriteLine("The Drive method invoked.");
}
}
//public class Testclass : staticclass // 4. Static
class is sealed. So static class cannot be inherited
//{
//}
class Test
{
static void Main(string[]
args)
{
// staticclass obj = new staticclass(); // static class cannot be instantiated
staticclass.method1();
// first constructor only executed
//staticclass.i
= 6;
Bus.Drive();
Console.ReadLine();
}
}
}
// static method
public class Bus
{
// Static constructor:
static Bus()
{
System.Console.WriteLine("The
static constructor invoked.");
}
public static void Drive()
{
System.Console.WriteLine("The
Drive method invoked.");
}
}
class TestBus
{
static void Main()
{
Bus.Drive();
}
}
// A static
constructor is called automatically to initialize and first called
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static
void Main(string[]
args)
{
Child
t = new Child();
}
}
class Parent
{
public
Parent()
{
Console.WriteLine("Parent Instance Constructor");
Console.ReadKey();
}
static
Parent()
{
Console.WriteLine("Parent Static Constructor");
Console.ReadKey();
}
}
class Child : Parent
{
public
Child()
{
Console.WriteLine("Child Instance Constructor");
Console.ReadKey();
}
static
Child()
{
Console.WriteLine("Child Static Constructor");
Console.ReadKey();
}
}
}
Output:
Child
Static Constructor
Parent
Static Constructor
Parent
Instance Constructor
Child
Instance Constructor
// Hash table
HashTable:
HashTable stores a key-value pair type collection of data.
NOTE:
Both key and value are object
Both key and value are object
the key values are UNIQUE
Functions:
1. Clear
2. Remove
3. Containskey
4. Containsvalue
5. Contains
6. Add
Variables
1. Count
Remove:
hash_table_name.Remove(key);
hash_table_name.Remove(key);
Remove All Values:
hash_table_name.Clear()
hash_table_name.Clear()
ContainsKey(Key)
its returns true or false..
its returns true or false..
ContainsValue(value):
EXAMPLE
Hashtable sampleHt = New Hashtable
sampleHt.add("US",”united States”) // Area- key. 1000 - value
sampleHt.add("IND",”India”)
Hashtable sampleHt = New Hashtable
sampleHt.add("US",”united States”) // Area- key. 1000 - value
sampleHt.add("IND",”India”)
// To fetch the value we
can use name, for example
String
countryname=convert.tostring(sampleHt[“US”]);
sampleHt.remove(“US”);
IDictionaryEnumerator idic= sampleHt.GetEnumerator();
while(idic.MoveNext())
{
idic.Value.ToString();
}
// Why c# not support
multiple inheritance?
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class A
{
protected
void samplemethod();
}
class B
{
protected
void samplemethod();
}
class C
: A, B
{
}
class Test
{
static void Main(string[]
args)
{
C
obj = new C();
obj.samplemethod(); // here which method to call now A or B?
}
}
}
Interface with objects:
using System;
using
System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public interface
IMyInterface
{
void
SomeMethod();
void
SomeOtherMethod();
}
public class
MyClass : IMyInterface
{
// Really
implementing this
public void SomeMethod()
{
Console.WriteLine("Interface object");
}
// Derived
class must implement this
public void SomeOtherMethod()
{
}
}
class Test
{
static void Main(string[]
args)
{
IMyInterface
obj = new MyClass();
obj.SomeMethod();
Console.ReadLine();
}
}
}
