Dotnet Interview Question

1. What is Property?
A property is a member that provides a flexible mechanism to read, write, or compute the value of a private field. Properties can be used as if they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily and still helps promote the safety and flexibility of methods.

Example:

class TimePeriod
{
    private double seconds;

    public double Hours
    {
        get { return seconds / 3600; }
        set { seconds = value * 3600; }
    }
}

2. What is the difference between abstraction and encapsulation?
Abstraction:
Abstraction lets you focus on what the object does instead of how it does it
That means we use the object without knowing the source code of the class.

Encapsulation:
Encapsulation means hiding the internal details or mechanics of how an object does something.
Encapsulation is warping data into single unit.


3. What is the difference between classes and structs in Microsoft.Net? 

• A struct is a value type, while a class is a reference type.
• When we instantiate a class, memory will be allocated on the heap, But when struct gets initiated, it gets memory on the stack.
• Classes can have explicit parameter less constructors. But structs cannot have this.
• Classes support inheritance. But there is no inheritance for structs. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Like classes, structures can implement interfaces.
• We can assign null variable to class. But we cannot assign null to a struct variable, since structs are value type.
• We can declare a destructor in class but can not in struct.

4. In which event are the controls fully loaded?
Page load event guarantees that all controls are fully loaded. Controls are also accessed in Page_Init events but you will see that view state is not fully loaded during this event.


5. How can we identify that the Page is Post Back?
Page object has an "IsPostBack" property, which can be checked to know that is the page posted back.

6. What is Query String? What are its advantages and limitations?
The Query String helps in sending the page information to the server.

The Query String has the following advantages:

• Every browser works with Query Strings.
• It does not require server resources and so does not exert any kind of burden on the server.

The following are the limitations of Query String:

• Information must be within the limit because URL does not support many characters.
• Information is clearly visible to the user, which leads to security threats.

7. What is View State?

The View State is a feature used by ASP.NET web page to store the value of a page and its controls just before posting the page. Once the page is posted, the first task by the page processing is to restore the View State to get the values of the controls.

8. How can you register a custom server control to a web page?
You can register a custom server control to a Web page using the @Register directive.
OR
You can also add in web config like below
<pages>
      <controls>
        <add assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagprefix="ajax"></add></controls></pages>

9.  What are the types of comment in C# with examples?

Single line

Eg:

[csharp]   //This is a Single line comment[/csharp]

ii. Multiple line (/* */)

Eg:

[csharp] /*This is a multiple line comment
We are in line 2
Last line of comment*/[/csharp]

iii. XML Comments (///).

Eg:

[csharp]/// summary;
///  Set error message for multilingual language.
/// summary[/csharp]

10. Can multiple catch blocks be executed?

No, Multiple catch blocks can’t be executed. Once the proper catch code executed, the control is transferred to the finally block and then the code that follows the finally block gets executed.

11. Can “this” be used within a static method?  

We can’t use ‘This’ in a static method because we can only use static variables/methods in a static method.

12. What is difference between constants and read-only?
Constant and ReadOnly keyword are used to make a field constant which value cannot be modified.

Constant

Constant fields or local variables must be assigned a value at the time of declaration and after that they cannot be modified. By default constant are static, hence you cannot define a constant type as static.
public const int X = 10;
A const field is a compile-time constant. A constant field or local variable can be initialized with a constant expression which must be fully evaluated at compile time.
void Calculate(int Z)
{
  const int X = 10, X1 = 50;
  const int Y = X + X1; //no error, since its evaluated a compile time
  const int Y1 = X + Z; //gives error, since its evaluated at run time
}
You can apply const keyword to built-in value types (byte, short, int, long, char, float, double, decimal, bool), enum, a string literal, or a reference type which can be assigned with a value null.
const MyClass obj1 = null;//no error, since its evaluated a compile time
const MyClass obj2 = new MyClass();//gives error, since its evaluated at run time
Constants can be marked as public, private, protected, internal, or protected internal access modifiers.
Use the const modifier when you sure that the value a field or local variable would not be changed.

ReadOnly

A readonly field can be initialized either at the time of declaration or with in the constructor of same class. Therefore, readonly fields can be used for run-time constants.
class MyClass {
  readonly int X = 10; // initialized at the time of declaration
  readonly int X1;

  public MyClass(int x1)
  {
    X1 = x1; // initialized at run time
  }
}
Explicitly, you can specify a readonly field as static since, like constant by default it is not static. Readonly keyword can be apply to value type and reference type (which initialized by using the new keyword) both. Also, delegate and event could not be readonly.
Use the readonly modifier when you want to make a field constant at run time.