no compatabiliyt
binary compatibility
project compatability etc

There are lot of threading model available, but we focus on 
threadingmodels that are common to win32based environments

singleThreaded:There is only one thread with in the 
process,and it is doing all the work for the process.The 
process must wait for the current execution of the thread 
to complete before it can perform another action.

Apartment Threading (Single Threaded Apartment)
Apartment threaded means there are multiple threads within 
the application. In single threaded apartment (STA) each 
thread is isolated in a separate apartment underneath the 
process. The process can have any number of apartments that 
share data through a proxy. The application defines when 
and for how long the thread in each apartment should 
execute. All requests are serialized through the Windows 
message queue such that only a single apartment is accessed 
at a time and thus only a single thread will be executing 
at any one time
Free Threading (Multi Threaded Apartment)
Free threaded applications were limited to programming 
languages such as C++ until the release of Microsoft .NET. 
The free threaded/Multi Threaded Apartment (MTA) model has 
a single apartment created underneath the process rather 
than multiple apartments. This single apartment holds 
multiple threads rather than just a single thread. No 
message queue is required because all of the threads are a 
part of the same apartment and can share data without a 
proxy.

The developer must provide thread synchronization as part 
of the code to ensure that threads do not simultaneously 
access the same resources

vb is not follow the oops concept.But vb.net follow the 
oops concept.

Adv of VB.NET
vb is object based.vb.net is object oriented
vb use record set for database connection
vb.net use dataset for database connection

1. VB uses vb runtime while vb.net uses CLR
2. VB object based,vb.net is object oriented
3. VB Suports splash screen 
4. VB Uses on error goto while vb.net uses Try.. 
Catch..Finally
5. vb.Net Supports inheritance

1)vb.net provide XML conversion
2)vb.net provide disconnect architecture 
3)vb.net object orineted base
4) any think is class

vb 6.0
1)not support XML
2)not support ado.net so no support disconnect architecture 
3)in vb first create class then call object

web user control where it predefined attribute functionality
where it resides in control library

web custom control: where it is defined by user itself and 
store in a custom library

Web User Controls:
1) Easy to Create
2) Limited support for consumers who use visual design tool
3) A seperate copy of the control is required in each 
application.
4)Cannot be added to toolbox in Visual Studio.
5) Good for Static Layout
Web Custom Controls:
1) Harder to Create
2) Full support for consumers
3) Only a single copy of the control is required in the GAC
4)Can be added
5) Good for Dynamic Layout

Plz refer the following link.It is very useful to know the 
difference b/w User control and Custom control and also how 
to create these controls.

http://support.microsoft.com/kb/893667

Kamal..........

Web User Control inherits .NET class i.e
System.web.UI.UserControl

whereas web custom control does not do so.

What are the basic differences between user controls and custom controls?
Now that you have a basic idea of what user controls and custom controls are and how to create them, let's take a quick look at the differences between the two.
Factors	User control	Custom control
Deployment	Designed for single-application scenarios

Deployed in the source form (.ascx) along with the source code of the application

If the same control needs to be used in more than one application, it introduces redundancy and maintenance problems	Designed so that it can be used by more than one application

Deployed either in the application's Bin directory or in the global assembly cache

Distributed easily and without problems associated with redundancy and maintenance
Creation	Creation is similar to the way Web Forms pages are created; well-suited for rapid application development (RAD)	Writing involves lots of code because there is no designer support
Content	A much better choice when you need static content within a fixed layout, for example, when you make headers and footers	More suited for when an application requires dynamic content to be displayed; can be reused across an application, for example, for a data bound table control with dynamic rows
Design	Writing doesn't require much application designing because they are authored at design time and mostly contain static data	Writing from scratch requires a good understanding of the control's life cycle and the order in which events execute, which is normally taken care of in user controls

you include the index parameter in the Property statement. 
In this example, the test_number parameter is the index for 
the Scores property.  
 
 
Public Class Student
    ' The private array of scores.
    Private m_Scores(9) As Integer

    ' The indexed Score property procedures.
    Public Property Score(ByVal test_number As Integer) As _
        Integer
        Get
            Return m_Scores(test_number)
        End Get
        Set(ByVal Value As Integer)
            m_Scores(test_number) = Value
        End Set
    End Property
End Class

main advantage of .net is versoning and solve very criticle 
problem.
.net maintain one application with more then one version
and also solve DLL HELL problem because it can run same 
application with diffrent version at a same time

.Net have an Assembly.It gives the Portable Execution 
file.The main use of assembly is to maintain the Dll and 
exe's.

So sometimes the programmer confused to which is modified 
code.That time the assembly provide the Version.

That is called versioning.

It is start from 1.0.*,.......

1.	Adding of a new virtual method to a class exported 
from a DLL can cause the following problems: 
o	If class already has a virtual method B and we are 
adding a new one named A before it, then we are changing 
the table of virtual methods. Now the first virtual method 
in the table will be A but not B and the client program 
which calls B will fail without recompilation as the call 
of B will cause the call of A and this is another method 
which possibly has other parameters and return type. 
o	When a class doesn?t have virtual methods and none 
of its base classes have, then adding of a new virtual 
method to it or to its base class will cause adding of the 
pointer for the table of virtual methods. This will cause 
change in the class size. So the error will occur after a 
client program will allocate memory for the class (an 
amount of memory that was required before the class has 
been changed) and will try to modify some of the class' 
fields explicitly or implicitly. In this case, as the 
pointer to the table of virtual method is added to the 
beginning of the class, all addresses of the class fields 
are shifted and thus we will get an abnormal client program 
behavior or a runtime error. 
o	In case when a class has virtual methods or any of 
its parent classes has, we can?t add virtual methods to 
classes exported from the DLL if they participate in the 
inheritance. We can?t add virtual methods not only to the 
beginning of the class declaration but also to the end of 
it. The problem is in shifting in the table of virtual 
methods. Note that even if you add a new virtual method to 
the end of the class declaration then the child?s virtual 
methods will be shifted. 
2.	Adding of a new field (of any kind) to a class 
declaration can cause following problems: 
1.	Adding of a new field to the end of a class causes 
class size to change as in the case of adding of a virtual 
method to a class that didn?t have any. The client program 
will allocate less memory than it is required for a new 
class and this will cause referencing to the memory out of 
the class scope. 
2.	Adding of a new field between existing ones is even 
worse. It will case all addresses of fields after the new 
one to be shifted and a client application will work with 
the incorrect addresses while working with the fields that 
are situated after the new field. We also have the problem 
as in the previous point here.

Overwriting a older version of dll by a new version of dll 
is known as Dll Hell problem.

Using command object we can execute a SP. Instead of sql 
query we have to pass the SP Name.

command.commection =coonectionstring
command.commandType=commandType.storedProcedure
command.commandtext="sp_name"
command.executenonquery()

Data reader is usefull when we just want to acccess datas 
from the database not when we want to perform DML 
operations. and  It is usefull when we want to perform 
forward only reading of datas.It wont requires any 
large volume of resources in the Front end.

Datareader is read only or forward only.So it is very fast 
to fetch the data from database.

1)it is used for forward record only.

2)we cannot update or save

3)speed is fast than dataset

4)not persist any record

5)it is usefual in case of display data according to 
critiera on form using control like textbox,label etc.

who to use

in vb.net
dim sqlcmd as new sqlcmd("select ename from tblemp where 
empid=5;
dim dr as new dataReader
dr=sqlcmd.executeReader()
if dr.hasRows then
txtbox1.text(dr("ename"))
end if

this display ename in textbox.

its connection oriented architecture.

Datareader is used to fetch the data frm data source

?  A DataSet can represent an entire relational database in 
memory, complete with tables, relations, and views.
?  A DataSet is designed to work without any continuing 
connection to the original data source.
?  Data in a DataSet is bulk-loaded, rather than being 
loaded on demand.
?  There's no concept of cursor types in a DataSet.
?  DataSets have no current record pointer You can use For 
Each loops to move through the data.
?  You can store many edits in a DataSet, and write them to 
the original data source in a single operation.
?  Though the DataSet is universal, other objects in 
ADO.NET come in different versions for different data 
sources. 

1) With Data set you can retrive data from database like 
oracle and SQL Server and manage them in one dataset, with 
recordset this is not possible.

2) All representation of Dataset is using XML while 
recordset uses COM.

3) Recordset can not be transmitted on HTTP while Dataset 
can be.

1) With Data set you can retrive data from database like 
oracle and SQL Server and manage them in one dataset, with 
recordset this is not possible.

2) All representation of Dataset is using XML while 
recordset uses COM.

3) Recordset can not be transmitted on HTTP while Dataset 
can be.

With Recordset comes the Recordset pointer, that points to 
the relative data so retrieved from the database. The 
Recordset object has MoveNext, MoveFirst, MovePrevious and 
MoveLast methods that provides a means for Data Traversal

With DataSet there is no pointer that points to the record, 
while a Bulk of Data is retrieved from the Database to the 
Computer's Memory, and the record is accessed via the index 
of the Record so retrieved.

With Recordset, has types of Cursors ie. Open Cursor and 
Data Manipulation Cursor, which enables the cursor to be 
open as read-only or dynamic (meaning for data 
manipulations)

With Dataset as bulk of data is loaded to the Memory, only 
Viewing operation is possible.

With Recordset, if the cursor is open as OpenDynamic and 
OpenOptimistic, the Data manipulated by 1 user, its effect 
is visible to the other user, leading to clear picture of 
the Database, while this is not the case in DataSet.

DataSet can be viewed as a ONE WAY HIGHWAY, where the data 
comes from Database to the Computer's Memory.
RecordSet can be viewed as a TWO WAY HIGHWAY, based on and 
according to the Cursor type selected in the recordset

The Recordset was not XML-based and could not be serialized 
to XML easily or flexibly.
Finally, a Recordset was not independent of a data store 
because it tracked a Connection object
and through its methods could send queries to the data 
source to populate, update,
and refresh its data.
To that end, the Recordset contained functionality found in 
the ADO.NET DataSet,
data reader, and data adapter objects.

Similar to the DataSet, a Recordset could be disconnected 
from its data store
and therefore act as an in-memory cache of data.
Of course, it could also be used in a connected model 
depending on the cursor options that were set.
Although the Recordset object stored multiple versions of 
each column for each of its rows,
it was not by nature able to represent multiple tables 
without the use of the Data Shape Provider.

1) With Data set you can retrive data from database like 
oracle and SQL Server and manage them in one dataset, with 
recordset this is not possible.

2) All representation of Dataset is using XML while 
recordset uses COM.

3) Recordset can not be transmitted on HTTP while Dataset 
can be

With Data set you can retrive data from database like 
oracle and SQL Server and manage them in one dataset, with 
recordset this is not possible.

2) All representation of Dataset is using XML while 
recordset uses COM.

3) Recordset can not be transmitted on HTTP while Dataset 
can be

dim dRow as data.datarow

for i as interger = 5 to 15
    drow = dSet.Tables(0).Rows(i)
    'process row
next i

For i as integer= 5 to 15 (Step 1)
   msgbox ds.tables(0).rows(i)
Next i

Datareader is forward and read only recordset in which the 
data manipultions are cant carried. but dataset is the 
miniature of database in which the datas can be accessed 
randomly and data manipulations can be carried

DataReader
Datareader is like a forward only recordset. It fetches one
row at a time so very less Network Cost compare to DataSet
(Fetches all the rows at a time). DataReader is readonly so 
we cannot do any transaction on them. DataReader will be 
the best choice where we need to show the data to the user 
which requires no transaction ie reports. Due to DataReader 
is forward only we cannot fetch the data randomly. .NET 
Dataproviders optimizes the datareaders to handle the huge 
amount of data.

DataSet
DataSet is always a bulky object that requires lot of 
memory space compare to DataReader. We can say the dataset 
as a small database coz it stores the schema and data in 
the application memory area. DataSet fetches all data from 
the datasource at a time to its memory area. So we can 
traverse through the object to get required data like 
qureying database.

The dataset maintains the relationships among the 
datatables inside
it. We can manipulate the realational data as XML using 
dataset.We can do transactions (insert/update/delete) on 
them and finally the modifications can be updated to the 
actual database. This provides impressive flexibility to 
the application but with the cost of memory space. DataSet 
maintains the original data and the modified data 
seperately which requires more memory space. If the amount 
of data in the dataset is huge 
then it will reduce the applications performance 
dramatically.

The following points will improve the performane of a 
dataset...

1. Don't use the commandbuilder to generate the sql 
statements.
Though it reduces the development time the query generated

by the command builder will not be always as required. For 
example
To update the details of an author table the command

Dataset is cache of records retrieve from data source.
Datareader is used to retrieve data from datasource.

1.Using Datareader we can read the data readnly,forwordonly 
basis.
2.Only one record in a memmory at a tme  
3.Faster
4.Doesnot hold any data
5.Data can not be transfer to datasource
Wher as in Dataset
1. we can read and write and allow us to navigate through 
the records forword and backwords.
2.Pulls the records from the datasource and saves in IIS 
memmory.
3.Slower
4.Holds datatables and has the information about
relationship between those tbes.
5.Data can be transfer to datasource

DataReader
Datareader is like a forward only recordset. It fetches one
row at a time so very less Network Cost compare to DataSet
(Fetches all the rows at a time). DataReader is readonly so 
we cannot do any transaction on them. DataReader will be 
the best choice where we need to show the data to the user 
which requires no transaction ie reports. Due to DataReader 
is forward only we cannot fetch the data randomly. .NET 
Dataproviders optimizes the datareaders to handle the huge 
amount of data.

DataSet
DataSet is always a bulky object that requires lot of 
memory space compare to DataReader. We can say the dataset 
as a small database coz it stores the schema and data in 
the application memory area. DataSet fetches all data from 
the datasource at a time to its memory area. So we can 
traverse through the object to get required data like 
qureying database.

Hi,

Static variables are declare through the 

Static Var1 as Integer

The scop of the Var1 is within the module where its is 
defined

Static variables retains their values even after the 
termination of the procedure in which it is declared.

Static variable are declared within the procedure.
and it preserves the value of variable.whether is 
called 10000 times.no problem.

overloading-------having same method name with different 
signatures.
 overriding--------methods name and signatures must be same.

OverLoading :  All the method will share the same name but 
it differes based on the parameter, type of parameter and 
number of parameter

Overriding : The method in the derived class the has the 
same name in the base class and it changes the behaviour or 
functionality of the method in the base class.

Overloading: Methods have different signature but same
behavior or functionality.

Overriding: Methods have same signature but different bevior
or functionality.

overloading has same method but different types of 
parameters, number of parameters.

overloading does not take return type to differentiate 
overloaded method.

ex:
int add(int a, int b)
int add(float a , float b)
are overloaded methods

overriding comes with inheritance concept.
here parent and child both contains the same method. and 
when execution takes place; child's method is called.

OVERLOADING is the process of declaring the methods having 
the same name but diff signatures. Signature means diff 
types & number of arguments.

OVERRIDING is the process of overwriting the methods of 
base class in Derived Class.

overriding: it just in inheritance  and the overriding
method must hold the same name and the same signatures .
the change maybe just in behavior .

overloading : maybe in inheritance or in other way but must
to do overloading must the method hold the same name and
must change signatures.
remark:we can not only change th return type.

1-OverLoading is Resolved at COMPILE TIME.But Overridding is
resolved at RunTime.

2-OverLoaded Methods Can Change Access specifiers.in
overridding the access level of overridden method(in derived
class) must not be more restrictive than that of overridden
method(of base class)

3-Overloaded methods can declare new exceptions.But
overridden method must not throw new exceptions than those
declared by overridden method.

overriding->
    1) method should be public.
    2)it need inheritance.
    3)it need virtual keyword before it declartion.
    4)it have same name with same parameter in diffrent   class.
    5)it require non-static method.
    6)method should have same datatype.
Overloading->
    1)method can be different access speicifier.
    2)it doesn't need inheritacne.
    3)all method should be in same class.
    4)method can have diffrent datatypes

OVERLOADING:- 1) overloaded methods have the same name but 
different parameter list.
2)a subclass method can overload a superclass method 

eg:-int add(int a, int b)
int add(float a , float b)
are overloaded methods



OVERRIDING:-
it just in inheritance  and the overriding
method must hold the same name and the same signatures .
the change maybe just in behavior .


The Cat class in the following example is the subclass and 
the Animal class is the superclass. The Cat class overrides 
eat() method inherited from Animal class.

public class Animal {

    public void eat() {
        System.out.println("Eat for Animal");
    }
}

public class Cat extends Animal {

    public void eat() {
        System.out.println("Eat for Cat");
    }
}

1-OverLoading is Resolved at COMPILE TIME.But Overridding is
resolved at RunTime.

2-OverLoaded Methods Can Change Access specifiers.in
overridding the access level of overridden method(in derived
class) must not be more restrictive than that of overridden
method(of base class)

3-Overloaded methods can declare new exceptions.But
overridden method must not throw new exceptions than those
declared by overridden

overloading-------having same function name but with
different signatures.
 overriding--------function name and signatures must be same.

When global and local varible  in the same name.
the local varibale in a mehod or function which use to 
override the global is called the shadowing.
ie the Global varible is being shadowed by the 
local varible

If there are overloaded methods in the base class, & u 
marks one of the methods as shadows using the keyword 
shadow in the derived class, then we cannot access the 
overloaded methods.

Ex-
public class base
  public sub test()
console.writeline("sonia")
 end sub

public sub test(i as integer)
 console.writeline(i)
end sub

end class

public sub derived
inherirts base
 shadows sub test(x as integer)
console.writeline("Shadow method")
end sub
end class


sub main()
dim obj as new derived
obj.test()-->Invalid
obj.test(10)-->Valid
end sub

Whatever the code written by Sonia.sardana is shows the 
shadowing concept but there is some print mistakes in the 
code.The correct code is---


imports system
module m1 
public class base
 Public Sub test()
        Console.WriteLine("sonia")
    End Sub

    Public Sub test(ByVal i As Integer)
        Console.WriteLine(i)
    End Sub

End Class

Public class derived
    inherits base

Shadows Sub test(ByVal x As Integer)
    Console.WriteLine("Shadow method")
End Sub
end class


Sub main()
    Dim obj As New derived
obj.test()  'This will show error
obj.test(10) 'This is valid
End Sub
    
end module