Difference between Overriding and Overloading

Difference between Overriding and Overloading

Overriding is the example of run-time polymorphism and
Overloading is the example of compile-time polymorphism.

Overriding
■The return type must exactly match that of the overridden method.
■The access level must not be more restrictive than that of the overridden method.
■The access level can be less restrictive than that of the overridden method.
■The overriding method must not throw new or broader checked exceptions than those declared by the overridden method.
■The overriding method can throw narrower or fewer exceptions. Just because an overridden method “takes risks” doesn’t mean that the overriding subclass’ exception takes the same risks. Bottom line: An overriding method doesn’t have to declare any exceptions that it will never throw, regardless of what the overridden method declares.
■You cannot override a method marked final.
■If a method can’t be inherited, you cannot override it.
Overloaded method
■Overloaded methods must change the argument list.
■Overloaded methods can change the return type.
■Overloaded methods can change the access modifier.
■Overloaded methods can declare new or broader checked exceptions.
■A method can be overloaded in the same class or in a subclass.

What is the difference between DELETE and TRUNCATE? Is one faster than the other?

DELETE logs the data for each row affected by the statement in the transaction log and physically removes the row from the file, one row at a time. The recording of each affected row can cause your transaction log grow massively if you are deleting huge numbers of rows. However, when you run your databases in full recovery mode, detailed logging is necessary for SQL Server to be able to recover the database to the most recent state, should a problem arise. The fact that each row is logged explains why DELETE statements can be slow.

TRUNCATE is faster than DELETE due to the way TRUNCATE "removes" rows. Actually, TRUNCATE does not remove data, but rather deallocates whole data pages and removes pointers to indexes. The data still exists until it is overwritten or the database is shrunk. This action does not require a lot of resources and is therefore very fast. It is a common mistake to think that TRUNCATE is not logged. This is wrong. The deallocation of the data pages is recorded in the log file. Therefore, BOL refers to TRUNCATE operations as "minimally logged" operations. You can use TRUNCATE within a transaction, and when this transaction is rolled-back, the data pages are reallocated again and the database is again in its original, consistent state.

Some limitations do exist for using TRUNCATE.

· You need to be db_owner, ddl_admin, or owner of the table to be able to fire a TRUNCATE statement.


· TRUNCATE will not work on tables, which are referenced by one or more FOREIGN KEY constraints.

So if TRUNCATE is so much faster than DELETE, should one use DELETE at all? Well, TRUNCATE is an all-or-nothing approach. You can't specify just to truncate those rows that match a certain criteria. It's either all rows or none.

You can, however, use a workaround here. Suppose you want to delete more rows from a table than will remain. In this case you can export the rows that you want to keep to a temporary table, run the TRUNCATE statement, and finally reimport the remaining rows from the temporary table. If your table contains a column with the IDENTITY property defined on it, and you want to keep the original IDENTITY values, be sure to enabled IDENTITY_INSERT on the table before you reimport from the temporary table. Chances are good that this workaround is still faster than a DELETE operation.

You can also set the recovery mode to "Simple" before you start this workaround, and then back to "Full" one it is done. However, keep in mind that is this case, you might only be able to recover to the last full backup.

What are triggers? How to invoke a trigger on demand?

Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table.

Triggers can't be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, DELETE) happens on the table on which they are defined.

Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster.

What is AJAX in ASP.Net

Ajax stands for Asynchronous Javascript & XML. It is a web technology through which a postback from a client (browser) to the server goes partially, which means that instead of a complete postback, a partial postback is triggered by the Javascript XmlHttpRequest object. In such a scenario, web-application users won't be able to view the complete postback progress bar shown by the browser. In an AJAX environment, it is Javascript that starts the communication with the web server.

Ajax technology in a website may be implemented by using plain Javascript and XML. Code in such a scenario may tend to look little complex, for which the AJAX Framework in .NET can be embedded in ASP.NET web applications.

In addition to XML & Javascript, AJAX is also based on DOM - the Document Object Model technology of browsers through which objects of the browser can be accessed through the memory heap using their address.

What is WPF in .Net

Windows Presentation Foundation (WPF) is Microsoft's development tool for Web applications and rich client applications.With WPF, developers can use XAML, the Extensible Application Markup Language, to create custom controls, graphics, 3D images and animations that are not available in traditional HTML implementations.

What is WCF in .Net 3.5

Windows Communication Foundation (WCF)
is Microsoft's programming model for using managed code to build unified Web services and other distributed systems that can talk to each other.
WCF focuses on connecting XML to programs that are built using development languages supported by Microsoft, such as VB.NET and C#.
To support this cross-language communication, WCF uses the extensible Simple Object Access Protocol (SOAP).

What is Web Services in .Net

In ASP.NET, a web service is essentially a listener that monitors a particular URL exposed via HTTP, looking for requests packaged as SOAP messages. When a request arrives, the ASP.NET runtime unpackages the request and calls the method for which the request is intended, passing in any parameters included with the request. If the request has a return value (which is not required), the ASP.NET runtime packages up the return value (based on the XML schema datatype specifications) and sends it to the client as a SOAP message. What this means to developers is that your application doesn't need to know anything about the client that will consume it, other than the fact that it can understand XML and SOAP. Thus, developers can essentially write methods that will be called as web services just as though they were writing methods that would be called locally.

This functionality is provided by the runtime largely for free. Developers expose their functionality as web services by marking their methods with a specific metadata attribute, the WebService attribute. The Common Language Runtime (CLR) takes care of the rest—from packaging and unpackaging SOAP requests to automatically providing HTML documentation of the web service—if it is called from a web browser (rather than by a SOAP request).