Interview Questions → CSHARP 2.0 → C# 2.0 Questionnaire II

C# 2.0 Questionnaire II

What is Persistent and Non-Persistent cookie?

Persistent cookies: cookies are stored on your computer hard disk. They stay on your hard disk and can be accessed by web servers until they are deleted or have expired.

Non-persistent cookies: cookies are saved only while your web browser is running. They can be used by a web server only until you close your browser. They are not saved on your disk.

What is the difference between const and readonly?

Const is defined at compile time and cannot be changed at run time. They must be initialized when declared.

public const int constVal = 2;

If you will not initialize the const variable when you declare it then a compile time error comes.

Readonly is like const, but we can change the value of readonly by assigning the new value in constructor.

public partial class Form1 : Form
{
  public readonly int readonlyVal = 2;
  public Form1()
  {
    readonlyVal = 5;
  }
}

Like const it is not necessary to initialize readonly at the time of declaration.

How can you throw both the programmer defined exception and .net generated exception simultaneously?

You can use inner exception

Consider an example in which you are trying to divide a number from zero

public void throwException()
{
  try 
  {
    int y = 0;
    int x = 5 / y;
  }
  catch (Exception ex)
  {            
    throw new Exception("This is the user friendly message",ex);
  }
}

Here you can in this function in the catch block I am throwing the exception in which I am giving the user friendly message and the object of the exception class.

throw new Exception("This is the user friendly message",ex);

Now you can catch the print both the messages on the front end using Message and InnerException.Message

i.e.

Response.Write(ex.Message); -- User Friendly Message
Response.Write(ex.InnerException.Message); -- .net generated message

What is the difference between throw and throw ex?

Consider an example to elaborate the difference

public void ErrorRoutine()
{
  int x = 0;
  int y = 5 / x;
}
public void Errorcatchingroutine()
{
  try
  {
    ErrorRoutine();
  }
  catch (Exception ex)
  {
     throw;
  }
}

Now call the method ErrorRoutine() when an exception occurs and catched, the stack trace is

at test.ErrorRoutine() in c:\Documents and Settings\karan\Desktop\ThrowEx\App_Code\test.cs:line 25 at test.Errorcatchingroutine() in c:\Documents and Settings\karan\Desktop\ThrowEx\App_Code\test.cs:line 35 at _Default.Page_Load(Object sender, EventArgs e) in c:\Documents and Settings\IDL2411\Desktop\ThrowEx\Default.aspx.cs:line 18

Now change the throw to throw ex in Errorcatchingroutine()

Now the stacktrace is

at test.Errorcatchingroutine() in c:\Documents and Settings\karan\Desktop\ThrowEx\App_Code\test.cs:line 35 at _Default.Page_Load(Object sender, EventArgs e) in c:\Documents and Settings\karan\Desktop\ThrowEx\Default.aspx.cs:line 18

As you can see in throw ex stacktrace is truncated.

What is the difference between a == b and a.Equals(b)?

There are 2 differences that I am listing here

• With Equals you can compare 2 variables of different data type but in case of a == b, a and b should be of same data type.

Consider the following code

string str = string.Empty;
int i = 0;
if (str == i)  // This line will give compile time errors.
{
	// Some Code
}
 if (str.Equals(i)) // This line of code will execute
{ 
	//Some Code
}

• a ==b compares value and a.Equals(b) compares object.

Consider an example

StringBuilder sb1 = new StringBuilder("karan");
StringBuilder sb2 = new StringBuilder("karan");
if (sb1.Equals(sb2)) // This condition will return true
{ }
if (sb1 == sb2) // This condition will return false
{}

What is interface overloading?

As the term overloading in OOPS means same name and multiple instances. In interface we can implement overloading of methods. As we all know that interface contains only signature of the methods.

Let us declare an interface having 2 methods with same name

public interface I1
{
    string Display();
    string Display(string displayString);
}

As seen in the code above there are 2 methods with same name but different number of parameters passed.

Now create a class that will inherit the interface and implement the above 2 methods.

public class test : I1
{
    public string Display()
    {
        return "null";
    }
    public string Display(string displayString)
    {
        return displayString;
    }
}

Now create the instance of the class and call both methods.

test obj = new test();
string str1 = obj.Display();
string str2 = obj.Display("Hi");
Response.Write(str1);
Response.Write(str2);

What is the difference between interface and abstract class?

      1. Interfaces have only methods prototype but no definition, but abstract class contains method definition also.

      2. If a class inherits an interface then it is required to implement all the methods in the class, but if a class inherits an abstract class then only methods which are abstract are required to be implemented.

      3. A class can inherit more than one interface, but can’t inherit more than one abstract class.

Can we override static method? Give Reason?

C# uses VTable or virtual method table to call the method at run time. For example if we have a class Cat

public class Cat
{
	public  SpeakType Speak()
	{
		.......
	}
}

public class HomeCat : Cat
{
	public  override SpeakType Speak()
	{
		.......
	}
}

In both the classes the entries of both the method is done into the VTable. So at runtime environment will bind the appropriate method call at run time.

In case of static method there is no entry of method in VTable so it is not possible to override the static method.

Is StringBuilder a data type?

Yes, stringbuilder is a datatype.

Reason - If you see the datatype definition on microsoft website you will see the following

A data type can be described as being either:

      1. A built-in data type, such as an int or char, or

      2. A user-defined data type, such as a class or interface.

      3. Data types can also be defined as being either:

            3.1 Value Types (C# Reference), which store values, or

            3.2 Reference Types (C# Reference), which store references to the actual data.

StringBuilder satisfies point 2 i.e. a user defined data type, such as class or interface and point 3.1 i.e. it is a type which stores value (In this case the value is of type string). Hence string builder is a data type.

What is the use of static constructor?

Static constructor is used to initialize static variables.

Consider following class

      public class StaticClassOne
      {
        private int variableOne;
        private static int variableTwo;

        static StaticClassOne()
        {
           variableTwo = 2;
        }
        public StaticClassOne()
        {
           variableOne = 5;
        }                
      }

Here in static constructor is used to initialize static variable variableTwo. You can also initialize the static variable in a non static constructor. But non static constructor is called every time an instance of class is formed. But static constructor is called only once i.e. when the first time the class is instantiated.

Consider the following code

      StaticClassOne obj = new StaticClassOne();
      obj = new StaticClassOne();

In the above code normal constructor is called twice because you are creating instance of the class twice but static constructor is called once i.e. when first line of code is called.

Posted By -

Karan Gupta

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