Top 10 Interview Questions on OOPS

.Net  Interview Questions and Answers on OOPS

1.       What is an Object in OOPS?

An object is a software bundle of variables and related methods. Objects are related to real life scenario. Class is the general thing and object is the specialization of general thingObjects is instance of classes.

 Declaration of an Object in OOPs

ClassName objectName=new ClassName();

E.g.: Person objPerson= new Person();

An object is characterized by concepts like:

•            Attribute

•             Behavior

•             Identity

2.            What is an Attribute in OOPs?

•        Attributes define the characteristics of a class.

•        The set of values of an attribute of a particular object is called its state.

•        In Class Program attribute can be a string or it can be a integer

3.            What is a Behavior in OOPS?

•        Every object has behavior

•        In C#, behaviors of objects are written in methods.

•        If a behavior of an object needs to be performed, then the corresponding method is called.

4.            What is an Identity in OOPS?

•        Each time an object is created the object identity is been defined.

•        This identity is usually created using an identifier which is derived from the type of item

5.           What is Encapsulation in OOPS?

•        Encapsulation is one of the fundamental principles of object-oriented programming.

•        Encapsulation is a process of hiding all the internal details of an object from the outside world

•        Encapsulation is the ability to hide its data and methods from outside the world and only expose data and methods that are required

•        Encapsulation is a protective barrier that prevents the code and data being randomly accessed by other code or by outside the class

•        Encapsulation gives us maintainability, flexibility and extensibility to our code.

•        Encapsulation makes implementation inaccessible to other parts of the program and protect from whatever actions might be taken outside the function or class.

•        Encapsulation provides a way to protect data from accidental corruption

•        Encapsulation hides information within an object

•        Encapsulation is the technique or process of making the fields in a class private and providing access to the fields using public methods

•        Encapsulation gives you the ability to validate the values before the object user change or obtain the value

•        Encapsulation allows us to create a "black box" and protects an objects internal state from corruption by its clients.

There are two ways to create a validation process.

1.            Using Assessors and Mutators

2.            Using properties

Benefits of Encapsulation

•        In Encapsulation fields of a class can be read-only or can be write-only

•        A class can have control over in its fields

•        A class can change data type of its fields anytime but users of this class do not need to change any code

6.  What is Inheritance in OOPS?

•                    Inheritance, together with encapsulation and polymorphism, is one of the three primary characteristics (concept) of object-oriented programming

•                    Inheritance enables you to create new classes that reuse, extend, and modify the behavior that is defined in other classes

•                    The Class whose methods and variables are defined is called super class or base class

•                    The Class that inherits methods and variables are defined is called sub class or derived class

•                    Sometimes base class known as generalized class and derived class known as specialized class

•                    Keyword to declare inheritance is “:” (colon) in visual c#

Benefits of using Inheritance 

•                    Once a behavior (method) or property is defined in a super class(base class),that behavior  or property is automatically inherited by all subclasses (derived class).

•                    Code reusability increased through inheritance

•                    Inheritance provide a clear model structure which is easy to understand without much complexity

•                    Using inheritance, classes become grouped together in a hierarchical tree structure

•                    Code are easy to manage and divided into parent and child classes

7. What is Polymorphism in OOPS?

•                    Polymorphism is one of the primary characteristics (concept) of object-oriented programming

•                    Poly means many and morph means form. Thus, polymorphism refers to being able to use many forms of a type without regard to the details

•                    Polymorphism is the characteristic of being able to assign a different meaning specifically, to allow an entity such as a variable, a function, or an object to have more than one form

•                    Polymorphism is the ability to process objects differently depending on their data types

•                    Polymorphism is the ability to redefine methods for derived classes.

Types of Polymorphism

•                    Compile time Polymorphism

•                    Run time Polymorphism

8. What is Compile Time Polymorphism in OOPS?

•                    Compile time Polymorphism also known as method overloading

•                    Method overloading means having two or more methods with the same name but with different signatures

9. What is Run Time Polymorphism in OOPS?

•                    Run time Polymorphism also known as method overriding

•                    Method overriding means having two or more methods with the same name , same signature but with different implementation

10. What is Access Modifier in OOPS?

Access modifiers determine the extent to which a variable or method can be accessed from another class or object

The following five accessibility levels can be specified using the access modifiers

•                            Private

•                            Protected

•                            Internal

•                            Protected internal

•                            Public

6 Steps to Enable Transactions in WCF

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Download the source code from here http://www.codeproject.com/KB/WCF/WCFTransactions/WCFTransactions.zip

Table of Contents

• Introduction and Goal
• Step 1: Create Two WCF Services
• Step 2: Attribute Interface Methods with TransactionFlow
• Step 3: Attribute the Implementation with TransactionScopeRequired
• Step 4: Enable Transaction Flow using WCF Service Config File
• Step 5: Call the 2 Services in One Transaction
• Step 6: Test If Your Transaction Works
• History
  
  

Introduction and Goal

In this article, we will try to understand how we can implement transactions in WCF service. So we will create two WCF services which do database transactions and then unite them in one transaction. We will first understand the 6 important steps to enable transactions in WCF services. At the end of the article, we will try to force an error and see how the transaction is rolled back after the error.

Step 1: Create Two WCF Services

The first step is to create two WCF service projects which will participate in one transaction. In both of these WCF services, we will do database transactions and we will try to understand how a WCF transaction unifies them. We have also created a web application with name WCFTransactions which will consume both the services in one transaction scope.

Step 2: Attribute Interface Methods with TransactionFlow

In both the WCF services, we will create a method called UpdateData which will insert into the database. So the first thing is to create the interface class with ServiceContract attribute and the method UpdateData with OperationContract attribute. In order to enable transaction in UpdateData method, we need to attribute it with TransactionFlow and we have specified that transactions are allowed for this method using TransactionFlowOption.Allowed enum.

[ServiceContract]
public interface IService1
{
[OperationContract]
[TransactionFlow(TransactionFlowOption.Allowed)]
void UpdateData();
}

Step 3: Attribute the Implementation with TransactionScopeRequired

The 3^rd step is to attribute the implementation of the WCF services with TransactionScopeRequired as true. Below is the code snippet which has a simple database inserting function, i.e. UpdateData which is attributed by TransactionScopeRequired attribute.

[OperationBehavior(TransactionScopeRequired = true)]
public void UpdateData()
{
SqlConnection objConnection = new SqlConnection(strConnection);
objConnection.Open();
SqlCommand objCommand = new SqlCommand("insert into Customer
        (CustomerName,CustomerCode) values('sss','sss')",objConnection);
objCommand.ExecuteNonQuery();
objConnection.Close();
}

Step 4: Enable Transaction Flow using WCF Service Config File

We also need to enable transactions for wsHttpBinding by setting the transactionFlow attribute to true.

<bindings>
<wsHttpBinding>
<binding name="TransactionalBind" transactionFlow="true"/>
</wsHttpBinding>
</bindings>

The transaction enabled binding we need to attach with the end point through which our WCF service is exposed.

<endpoint address="" binding="wsHttpBinding" 
        bindingConfiguration="TransactionalBind" contract="WcfService1.IService1">

Step 5: Call the 2 Services in One Transaction

Now that we are done with enabling our server side transaction, it’s time to call the above 2 services in 1 transaction. We need to use the TransactionScope object to group the above 2 WCF services in one transaction. To commit all the WCF transactions, we call the Complete method of the Transactionscope object. To rollback, we need to call the Dispose method.

using (TransactionScope ts = new TransactionScope(TransactionScopeOption.RequiresNew))
{
try
{

// Call your webservice transactions here
ts.Complete();
}
catch (Exception ex)
{
ts.Dispose();
}
}

Below is the complete code snippet in which we have grouped both the WCF transactions in one scope as shown below:

using (TransactionScope ts = new TransactionScope(TransactionScopeOption.RequiresNew))
{
try
{
ServiceReference1.Service1Client obj = new ServiceReference1.Service1Client();
obj.UpdateData();
ServiceReference2.Service1Client obj1 = new ServiceReference2.Service1Client();
obj1.UpdateData();
ts.Complete();
}
catch (Exception ex)
{
ts.Dispose();
}
}

Step 6: Test If Your Transaction Works

It’s time to test if the transactions really work. We are calling two services, both of which are doing an insert. After the first WCF service call, we are forcing an exception. In other words, the data insert of the first WCF service should revert back. If you check the database records, you will see no records are inserted by the WCF service.

History

• 6^th August, 2009: Initial post