Partial classes is a new feature of OOPs in .NET2.0 

Partial classes means split the class into multiple files.


For example 

             u r working with windows applications actually
designer.cs is using a class like webform1, u can use this
class in other cs file also.

using a partial class, we can split a class into multiple 
files.
compiler will treat them as different classes.
but when compiled all the files will be treated as a single 
class.
it is more efficeint

One of the greatest benefits of partial classes is that it 
allows a clean separation of business logic and the user 
interface (in particular the code that is generated by the 
visual designer). Using partial classes, the UI code can be 
hidden from the developer, who usually has no need to 
access it anyway. Partial classes will also make debugging 
easier, as the code is partitioned into separate files.

Partal classes can help in segregating code with respect 
type like tool visual Studio generated,default imported 
namespaces , events registration , variable declaration 
code etc. It is best to split lengthy code into smaller 
units but dealing them with same class Object

through partial keyword we can split the defination of the 
class in different source files and these definations are 
combined when application is compiled.

it may be helpful in large projects,so many people can work 
on same class

Can you u explain me the code for the partaial class?

File 1.
partial class Employee 
{
 string employeename;
 public void getEmployeeName(string empname)
 {
   employeename = empname;
 }
 
 public static void Main()
 {

  Employee objEmployee = new Employee();
  objEmployee.getEmployeeName("Krish");
  objEmployee.showEmployeeName();
  Console.ReadLine();
 }

}
File 2

partial class Employee
 {
  public void showEmployeeName()
  {
    Console.WriteLine("Name --->" + employeename);
  }

 }

Even though the method showEmployeeName is not a available 
in file 1 since  its partial class the complier would 
combine the fragments of the file that corresponds to same 
class.

The purpose of partial classes is to allow a class's
definition to span across multiple files. It is especially
useful for:

Allowing multiple developers to work on a single class at
the same time without the need for later merging files in
source control.

Allowing a separation between the class interface and the
implementation-related definitions

Easing the writing of code generators, such as visual designers.

Partial class is a new functionality that is included in 
Visual Studio .Net 2005 and is supported in ASP.Net 2.0. 
This new functionality helps you to split a single class 
into multiple partial classes. These partial classes can be 
in different individual files.

Partial Class Means That At  Compilation Time Your Code 
Behind File And Web Form Are Now Merged Into One Class File.

Partial class is th one feature in V2.0 where you can split 
the functionalty of the single file in multiple files.

This is helpful on working simultaneously on same file, 
clearly separates Business Logic and UI, separets logic 
from single file to multiple files.

File1
Imports system
Interface IPartialInterface

sub abc( byval str as string)
sub abc()
End interface

Partial Class DemoPartialClass
dim strName a string
strName = "Anil"
Response.Write(strName)
End Class

File2

Imports system
Implements IPartialInterface

Partial Class DemoPartialClass
Public sub abc(ByVal strName as string)
Dim strValue as string
strValue = strName
End Sub
End Class

File 3

Imports system
Implements IPartialInterface

Partial Class DemoPartialClass
public sub abc()
response.write(strName)
End Sub
End Class