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15 September 2013

OOPs Concepts: When to use

Hai Friends,

This post is regarding the main OOPs concepts and what is there use and when it’s good to use them.

Below are the concepts which are included in this post:

·                     Encapsulation
·                     Abstraction
·                     Overloading
·                     Method Overriding
·                     Constructor
·                     Interface
·                     Inheritance
·                     Abstract class
These OOPs concepts you can use while implementing the functionality of your projects in accordance with the requirements and situations.
Hope it will be useful to learn and in the implementation of the projects.
1) In which situation encapsulation is used in your project?
Encapsulation is hiding and binding of the data.
Accessing the public properties by using private variables is one of the good examples of Encapsulation in all the projects.
private string _name;
public String Name
get{return _name}
set{_name= value;}

Here you are not able to access the private variable _name but its value can be accessible by the public property Name. So a kind of Encapsulation here. Namespace is also an example of Encapsulation which is encapsulating the classes, methods, properties etc.
This is the runtime behaviour of an entity.

2) In which situation abstraction is used in your project?
Hiding the behaviour and showing the necessary things regards an entity can be called as Abstraction. Like for a Car, showing the method like Clutch, Gear etc but hiding its internal functions can be an example of Abstraction. This is the compile time behaviour of the entities.
When there are the specific requirements and that can be flown to their child, then we can use abstraction. it means whatever is essential, we implement to its child classes, else will be inherited automatically.
class A
public abstract void Add(int a, int b);
protected int x;
public string Name{get; set;};
Class B: A
 public override void Add(int a, int b)
  Console.WriteLine("Sum of two numbers is:" + int. Parse(a + b).toString());
Here the essential method Add is implemented to the child class B. rest all the members will be inherited accordance to their protection levels.

3) In which situation method overloading is used in your project?
The concept where we want the similar functionality but different behaviour, we use overloading.
When we have same functionality to implement with different behaviour, we go with the overloading of method.
e.g. If we have to get the sum of 2 numbers, 3 number and 4 numbers. So in that case we can take only one method name Add with its varied parameters like:

public void Add(int a, int b)
 Console.WriteLine("Sum of 2 numbers" + int. Parse(a + b).toString());

public void Add(int a, int b, int c)
 Console.WriteLine("Sum of 3 numbers" + int. Parse(a + b +c).toString());

public void Add(int a, int b, int c, int d)
 Console.WriteLine("Sum of 4 numbers" + int. Parse(a + b + c + d).toString());

Now according to our requirement, we can call the respective method with its arguments.
Here all the methods are doing sum of the numbers, but their behaviour are different- the first method will give the sum of 2 number while the next one will give the sum of 3 number and the final method will give the sum of 4 numbers.

4) In which situation method overriding is used in your project?
When we may(abstract) or may not(virtual) want to implement the particular method at runtime to its child class according to the requirement, we go with overriding concept.

Class X
 public virtual void Print()
  Console.WriteLine ("This is the print method. You can override according to your definitions and implementation");
Class Y:X
 public Override void Print()
  Console.WriteLine("Implementation for Excel print methods");

5) In which situation constructor is used in your project?
Constructor is the way to initialize the class with the default values of the members. Constructor is by default initialize with the class.
But if you want to initialize some members when the class in getting instantiate, you can write the constructor and code for initialization inside that constructor.

Class MyClass
{int a;
 public MyClass()
   a=10; //initialized with the class instantiation

Here the constructor code will get initialized with the class instantiation.

6) In which situation interface is used in your project?
Interface is the collection of abstract members.
So whenever we have the requirements such as it requires through the application at many places, then we create an interface with that method so that we can implement it at our own way according to the requirements.
Interface Inf
 void Print();

Class ExcelClass:Inf
 public override void Print()
  //Write code to print in excel

Class WordPrintClass: Inf
 public override void Print()
  //Write code to print in Word
Class PDFPrintClass: Inf
 public override void Print()
  //Write code to print in PDF

Also to implement the multiple inheritances, we use inheritance.

7) In which situation inheritance is used in your project?
When we want to have some common features for multiple classes then we go for inheritance.
To inherit the properties of base class to their derived class.
8) In which situation abstract class is used in your project?
Abstract class is same as abstract. So go to the Q 2 for the details.

So you can go through the link to get the fair idea about its implementation:

7 September 2013

Interview Question for 3-6 Year experience in .Net Technologies-PART -II

Hai Friends,

With lot of encouragement and support, I am posting the Part II of the questions and answers for 3-6 years experienced people. These questions will be helpful for those who are preparing for the interview or attending the interviews. This will be helpful for the last minute preparation in quickest way.
If anyone has better answer, please reply to this post and I will include them.

C# / .Net framework / other .Net related questions:

1. What is the difference between IEnumerable and IQueryable?
Ans. IEnumerable and IQueryable are used to query data from collections and database.  The IEnumerable is basically inherited from IQueryable, so it’s having all the features of the IQueryable in addition to its having additional own features.

Exists in System.Collections Namespace
Exists in System.Linq Namespace
Can move to forward only in the collection.
Can move to forward, backward or in between the items.
Best for collection like List, Array or in-memory collection
Best for the collections which is out memory like services, remote databases etc
Suitable for LINQ to Object and Linq to XML queries.
Suitable for Linq to SQL queries
It doesn’t supports custom query, Lazy loading so it’s not good for paging scenarios.
It supports custom query using CreateQuery and Execute methods. Also support lazy loading so good for the paging scenarios.
The extension methods which supports be IEnumerable, takes the functional objects as the parameters.
The extension methods which supports be IQueryable, takes the expression tree as the parameters.

In the first example (By using the IEnumerable), the generated SQL is as below:

In the second example (By using the IQueryable), the generated SQL is as below:
We can see that by using the IQueryable, the performance will increase as it has the TOP clause in the query.

2. What is cross site scripting? (XSS)
Ans. Cross-site scripting is the way to attacks and insert the vulnerabilities in Web page. This attack is injected by client-side code. The script which is inject by the client can embed itself in response data. The response data which send back to the malicious user. The browser can’t recognize the scripts as it is responded from the trusted source.
The cross-site scripting attacks also work on the HTTP and HTTPS.
There are 2 ways to prevent the cross site scripting attack:
Constrain input- Validate the input length, type, formatting, range etc
Encode output- Send the input data with encode e.g. Encode to HTML
To prevent the cross-site attack, we can set the below attributes in web.config file: 
3. If I want to see my website similar in all the browsers then what I need to do for that?
Ans. If you want to see the website with the same look and feel then you need to write the common css style which should be same for all browsers. Actually every browser will not support every css elements so it is not possible to use the same css to support all the browsers. You need to write the common css elements in the file and then apply it across the website. Else you need to write the separate css file as per the browser.

4. If say 1 Lac users are using any particular website then what you will do to prevent crashing of server? Which care you will take at the time of coding?
Ans. There are the ways like we can have multiple servers to handle the requests from the users. In this, we can have the Web Gardening concept where we can have the multiple web servers and then one main server to handle the number of requests and switch the requests to other servers.

5. Why to use design patterns?
Ans. Design Pattern is the way to solve the recurring problems which occur during the designing of the applications. As the requirements increases, the projects becomes complex and due to the complexity, it’s difficult to maintain it.
With the help of design patterns, we can reduce the complexity and with the help of OOPs paradigm, we can make our applications more efficient in all the ways.
According to the GoF (Gang of Four) company, the Design Patterns can be classified to 3 ways:-
  • Creational Design Pattern
  • Behavioral Design Pattern
  • Structural Design pattern
6. If I have a class C and two interfaces I1 and I2 and I have 'Add' method inside I1 and I2 then how to specify which one has to be called?
Ans. By using the explicit implement interface, we can implement the same method which is defined in both the interfaces.
The implementation will be as below:
7. Garbage collection uses which type of algorithm? How it will find which object is unused?
Ans. Mark-And-Release is the algorithm which the garbage collection uses to reclaim the memory of the unreferenced objects which are no longer used.
The algorithm Mark-and-Release work in 2 steps:-
a.    In the first steps, it marks all the accessible objects of the heap memory. This is called as mark phase.
b.    In the second step, scan the heap and reclaim all the unmarked objects by the Garbage Collection algorithm. This step is called as sweep phase.
Below are the algorithm steps:
For the detailed description, follow the below link:
8. What is the difference between out and ref?
Ans: Ref and Out are the parameters which are used in the methods  [ref] and [out] both allows the called method to modify a parameter. The difference between them is what happens before you make a call.
  • [ref] means that the parameter has a value on it before going into the function. The called function can read and or change the value any time. The parameter goes in, then comes out
  • [out] means that the parameter has no official value before going into the function. The called function must initialize it. The parameter only goes out.
So the main difference between the ref and out parameter is that the out parameter doesn't needs to be initialized while the ref parameter must be initialized before passing to the function.

9. Is it possible to use more than one out parameter?
Ans.  As we know that the method always returns a single value but by using the out parameter, we can return multiple values from the method or function.
In C# we can write the small code snippet which will describe to return the multiple values using the out parameters:
We can also use the struct which will contain the multiple values as the return:

There is another way to return multiple values like using Tuple class (newly introduced in .Net 4.0). The tuple class can return the object which can contain multiple values in it. 

10. Is it possible to use .js files used under script will be in body and not in header? Why?
Ans. The .js file is used in header because first the .js file should be loaded to the application and then rest of the content should be load.

11. What is Expression Tree in C#? How to use Express Trees to create Dynamic LinQ queries?

Ans. Expression Tree is used to create Dynamic Linq query. Sometimes, when the specific criterias' can't be defined at compile time, Expression tree is useful to generate the Linq query at the runtime.
For E.g. In an application, the filter criteria is based on some user actions and is generated dynamically. In this case, we can use the Expression Tree which will generate the criteria at runtime and then we can use that criteria to filter the records from the IQueryable collection.
System.Linq.Expressions is the namespace required to work with the Expression Tree. Here we need to create the predicates using expressions, which will be used in the query.

Hope these questions and answers will be helpful to you.