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Can you describe IUKNOWN interface in short ?

Posted By :Shashi Ray     Posted Date :March 16, 2009    Points :10   Category :ADO.Net 
Every COM object supports at least one interface, the IUnknown interface. All interfaces are classes derived from the base class IUnknown. Each interface supports methods access data and perform operations transparently to the programmer. For example, IUnknown supports three methods, AddRef, Release(), and QueryInterface(). Suppose that pinterf is a pointer to an IUnknown. pinterf->AddRef() increments the reference count. pinterf->Release() decrements the reference count, deleting the object when the reference count reaches zero. pinterf->QueryInterface( IDesired, pDesired) checks to see if the current interface (IUnknown) supports another interface, IDesired, creates an instance (via a call to CoCreateInstance()) of the object if the reference count is zero (the object does not yet exist), and then calls pDesired->AddRef() to increment the reference count (where pDesired is a pointer to IDesired) and returns the pointer to the caller.

You can also find related Interview Question to Can you describe IUKNOWN interface in short ?  below: 

Can you describe IUKNOWN interface in short?

  
Every COM object supports at least one interface, the IUnknown interface.

All interfaces are classes derived from the base class IUnknown. Each interface supports methods access data and
perform operations transparently to the programmer.

For example, IUnknown supports three methods, AddRef, Release(), and QueryInterface().
Suppose that pinterf is a pointer to an IUnknown.

pinterf->AddRef() increments the reference count. pinterf->Release() decrements the reference
count, deleting the object when the reference count reaches zero.

pinterf->QueryInterface( IDesired,pDesired) checks to see if the current interface (IUnknown) supports another interface, IDesired,
creates an instance (via a call to CoCreateInstance()) of the object if the reference count is zero (the
object does not yet exist), and then calls pDesired->AddRef() to increment the reference count
(where pDesired is a pointer to IDesired) and returns the pointer to the caller. (More...)

Real software is developing a speech-based user interface for blind people. However, speech based interface are difficult to design and time given by the client is short. To develop a functional interface without any errors, the company wants to first evaluate the prototype. They used the storyboard technique to demonstrate the functionality of the application. However, this technique was unable to demonstrate the interactive feature of the application. Analyze and provide solution for the above scenario?

  
1, The design team of Real software should have used the Sketching technique because storyboard technique would only provide the flow and features of the interface.

2, The design team of Real software should have used the Horizontal Prototyping because storyboard technique would only provide the flow of the interface.

3, The design team of Real software should have used the Wizard of Oz technique because storyboard technique would only provide the flow and features of the interface

4, The design team of Real software should have used the Vertical Prototyping because storyboard technique would only provide the flow of the interface.


Answer : 3 (More...)

What is the difference between interface and abstract class ?

  
a class may inherit several interfaces, a class may inherit only one abstract class (More...)

Describe the three levels of data abstraction?

  
The are three levels of abstraction:
1.Physical level: The lowest level of abstraction describes how data are stored.

2.Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.

3.View level: The highest level of abstraction describes only part of entire database. (More...)

Describe ways of cleaning up objects.

  
The run time will maintain a service called as garbage collector.
this service will take care of deallocating memory corresponding to
objects.it works as a thread with least priority.when application
demenads for memory the runtime will take care of setting the high
priority for the garbage collector,so that it will be called for execution
and memory will be released.the programmer can make a call
to garbage colector by using GC class in system name space. (More...)

Describe the techniques for optimising your application?

  
. Avoid round-trips to server. Perform validation on client.
. Save viewstate only when necessary.
. Employ caching.
. Leave buffering on unless there is a dire need to disable it.
. Use connection pooling.
. Use stored procedures instead of in-line SQL or dynamic SQL. (More...)

What is difference between interface inheritance and class inheritance?

  
We can only inherit from one class but multiple interfaces. In addition, an interface does not contain any implementation it just contains a series of signatures. (More...)

What is difference between abstract class and an interface?

  
An Abstract class is a class with some common/certain implementations and defines abstraction for other services which are implemented in its concrete sub classes, whereas interface only have method declaration with zero implementations. An abstract class and Interface both have method only but not have body of method. The difference between Abstract class and An Interface is that if u call Abstract class then u have to call all method of that particular Abstract class but if u call an Interface then it is not necessary that u call all method of that particular interface. An abstract class is a special kind of class that cannot be instantiated. So the question is why we need a class that cannot be instantiated? An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for all the subclasses. In simple words, it is a kind of contract that forces all the subclasses to carry on the same hierarchies or standards.

An interface is not a class. It is an entity that is defined by the word Interface. An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that is used to define hierarchies for all subclasses or it defines specific set of methods and their arguments. The main difference between them is that a class can implement more than one interface but can only inherit from one abstract class. Since C# doesn't support multiple inheritance, interfaces are used to implement multiple inheritance.


Shashi Ray (More...)

What is transact-SQL? Describe its types?

  
Types of Transact-SQL:
----------------------
SQL Server Provides three types of Transact-SQL statements namely DDL, DCL, and DML.

Data Definition Language (DDL):
--------------------------------
It allows creating, altering and dropping database objects.

Data Control Language (DCL):
----------------------------
It is used to control access to data in the database.
It controls permission on the database objects using grant, revoke or deny statement.

Data Manipulation Language (DML):
--------------------------------
It involves retrieval, insertion, deletion, modification in the database.
It includes select, insert, update, and delete command. (More...)

Can you describe WCF ?

  
In Simple words, WPF stands for Windows Presentation Foundation.

In detailed view WPF is a new library to create the UI for smart client applications. Most noteable point is : application does not use Window handles. It is easy to resize the UI and supports sound video.


Definition of WPF is : 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. (More...)

Can you describe WPF?

  
In Simple words, WPF stands for Windows Presentation Foundation.

In detailed view WPF is a new library to create the UI for smart client applications. Most noteable point is : application does not use Window handles. It is easy to resize the UI and supports sound video.


Definition of WPF is : 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. (More...)

Describe the accessibility modifier protected internal.

  
It's available to derived classes and classes within the same Assembly. (More...)

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