Partial Class sealed class

Partial Class

In this article I will explain what is a partial class? What are the benefits of using partial classes and how to implement partial classes in your C# applications.

Partial class is a new feature added to C# 2.0 and Visual Studio 2005. It is supported in .NET Framework 2.0. If you are working with .NET 1.0 or 1.1, partial classes may not work.

It is possible to split the definition of a class or a struct, or an interface over two or more source files. Each source file contains a section of the class definition, and all parts are combined when the application is compiled.

When working on large projects, spreading a class over separate files allows multiple programmers to work on it simultaneously.

When working with automatically generated source, code can be added to the class without having to recreate the source file. Visual Studio uses this approach when creating Windows Forms, Web Service wrapper code, and so on. You can create code that uses these classes without having to edit the file created by Visual Studio.

Benefit of partial classes:

1) More than one developer can simultaneously write the code for the class.

2) You can easily write your code (for extended functionality) for a VS.NET generated class. This will allow you to write the code of your own need without messing with the system generated code.

There are a few things that you should be careful about when writing code for partial classes:
All the partial definitions must proceeded with the key word "Partial".
All the partial types meant to be the part of same type must be defined within a same assembly and module.
Method signatures (return type, name of the method, and parameters) must be unique for the aggregated typed (which was defined partially).
The partial types must have the same accessibility.
If any part is sealed, the entire class is sealed.
If any part is abstract, the entire class is abstract.
Inheritance at any partial type applies to the entire class.

sealed class:-
We just saw how to create and use a sealed class. The main purpose of a sealed class to take away the inheritance feature from the user so they cannot derive a class from a sealed class. One of the best usage of sealed classes is when you have a class with static members. For example, the Pens and Brushes classes of the System.Drawing namespace.

The Pens class represent the pens for standard colors. This class has only static members. For example, Pens.Blue represents a pen with blue color. Similarly, the Brushes class represents standard brushes. The Brushes.Blue represents a brush with blue color.

So when you're designing your application, you may keep in mind that you have sealed classes to seal user's boundaries.

* Support for Multi-targeting
* Integrated Ajax Support
* Support for Split View
* Integrated Silverlight Support
* LINQ
* Support for inbuilt Silverlight SDK
* Support for inbuilt C++ SDK
* Support for Multilingual User Interface
* Support for Nested Master Pages
* Support for JavaScript Debugging
* Support for JavaScript Intellisense

Visual Studio 2008 - New Features

* Multi-Targeting support
* Web Designer and CSS support
* ASP.NET AJAX and JavaScript support
* Project Designer
* Data
* LINQ � Language Integrated Query

SQL Question:

1.Name the classes are found in System.Data.Common NameSpace?
Ans:
DataColumnMapping
2)DataTableMapping

2. Can a table have two primary keys?
Ans:-A table can have Only One Primary key. But a table can have
composite Primary key. that means we can create composite
primary key .
upto 16 columns only.

3. select highest salary without using "top" ?
Ans:SELECT MAX(Salary) ThirdHighest
FROM Employee t
WHERE Salary <
(SELECT MAX(Salary)
FROM Employee t
WHERE Salary <
(SELECT MAX(Salary)
FROM Employee t));

4. select highest salary using "top" ?

SELECT TOP 1 salary
FROM (
SELECT DISTINCT TOP n salary
FROM employee
ORDER BY salary DESC) a
ORDER BY salary

Name the classes that are contained in System.Data NameSpace?

DataSet
DataTable
DataColumn
DataRow
DataRealation
Constraint