What are Object Initializers in C#
The Object initializers are the features for programming concepts which was introduced in C#.Net.
The aim of using Object Initializers is to intializing the accessible fields or properties
of an object without the need to write any parameterized constructor or separate
statements.
Sample:
using System;
class Student
{
int rollno;
string stdName;
static void Main()
{
Student s = new Student() { rollno=1,stdName="Ramesh" }; //Object Initializer
}
}
What are the fundamental differences between value types and reference types?
C# divides types into two categories – value types and reference types. Most of the intrinsic types (e.g. int, char) are value types. Structs are also value types. Reference types include classes, arrays and strings. The basic idea is straightforward – an instance of a value type represents the actual data, whereas an instance of a reference type represents a pointer or reference to the data.The most confusing aspect of this for C++ developers is that C# has predetermined which types are represented as values, and which are represented as references. A C++ developer expects to take responsibility for this decision
Working with Dictionary Collections
Another very useful generic collection is the Dictionary, which works with key/value pairs. There is a non-generic collection, called a Hashtable that does the same thing, except that it operates on type object. However, as explained earlier in this lesson, you want to avoid the non-generic collections and use thier generic counterparts instead. The scenario I'll use for this example is that you have a list of Customers that you need to work with. It would be natural to keep track of these Customers via their CustomerID. The Dictionary example will work with instances of the following Customer class:
public class Customer
{
public Customer(int id, string name)
{
ID = id;
Name = name;
}
private int m_id;
public int ID
{
get { return m_id; }
set { m_id = value; }
}
private string m_name;
public string Name
{
get { return m_name; }
set { m_name = value; }
}
}
The Customer class above has a constructor to make it easier to initialize. It also exposes it's state via public properties. It isn't very sophisticated at this point, but that's okay because its only purpose is to help you learn how to use a Dictionary collection. The following example populates a Dictionary collection with Customer objects and then shows you how to extract entries from the Dictionary:
Dictionary
Customer cust1 = new Customer(1, "Cust 1");
Customer cust2 = new Customer(2, "Cust 2");
Customer cust3 = new Customer(3, "Cust 3");
customers.Add(cust1.ID, cust1);
customers.Add(cust2.ID, cust2);
customers.Add(cust3.ID, cust3);
foreach (KeyValuePair
{
Console.WriteLine(
"Customer ID: {0}, Name: {1}",
custKeyVal.Key,
custKeyVal.Value.Name);
}
Whats the difference betweeen Structure, Class and Enumeration
Structures and Enumerations are Value-Types. This means, the data that they contain is stored as a stack on the memory. Classes are Reference-Types, means they are stored as a heap on the memory.
Structures are implicitly derived from a class called System.ValueType. The purpose of System.ValueType is to override the virtual methods defined by System.Object. So when the runtime encounters a type derived from System.ValueType, then stack allocation is achieved. When we allocate a structure type, we may also use the new keyword. We may even make a constructor of a structure, but, remember, A No-argument constructor for a structure is not possible. The structure's constructor should always have a parameter.
So if we define the following structure
struct MyStruct
{
public int y,z;
}
and we create a structure type
MyStruct st = new MyStruct();
In case of a class, no-argument constructors are possible. Class is defined using the class keyword.
A struct cannot have an instance field, whereas a class can.
class A
{
int x = 5; //No error
...
}
struct
{
int x = 5; //Syntax Error
}
A class can inherit from one class (Multiple inheritance not possible). A Structure cannot inherit from a structure.
Enum is the keyword used to define an enumeration. An enumeration is a distinct type consisting of a set of named constants called the enumerator list. Every enumeration has an underlying type. The default type is "int". Note: char cant be the underlying data type for enum. First value in enum has value 0, each consequent item is increased by 1.
enum colors {red, green, blue, yellow};
Here, red is 0, green is 1, blue is 2 and so on.
An explicit casting is required to convert an enum value to its underlying type
int x = (int)colors.yellow;
Explain constructor and destructor with an example using C#.NET.
Explain constructor and destructor with an example using C#.NET.
A constructor is a member function that performs the task of initializing the objects with the default values to be assigned after creation.
A destructor is a function that is run to release the resources held by an object when it is no longer needed by the application.
In C#.NET we can create constructor and destructor in the following manner:
-----------------CONSTRUCTOR---------
class C
{
private int x;
private int y;
public C (int i, int j)
{
x = i;
y = j;
}
public void display ()
{
Console.WriteLine(x + "i+" + y);
}
}
-----------------DESTRUCTOR---------
class D
{
public D()
{
// constructor
}
~D()
{
// Destructor
}
}
C# Interview Questions and Answers
1) The C# keyword ?int? maps to which .NET type?
-
System.Int16
-
System.Int32
-
System.Int64
-
System.Int128
2) Which of these string definitions will prevent escaping on backslashes in C#?
-
string s = #?n Test string?;
-
string s = ??n Test string?;
-
string s = @?n Test string?;
-
string s = ?n Test string?;
3) Which of these statements correctly declares a two-dimensional array in C#?
-
int[,] myArray;
-
int[][] myArray;
-
int[2] myArray;
-
System.Array[2] myArray;
4) If a method is marked as protected internal who can access it?
-
Classes that are both in the same assembly and derived from the declaring class.
-
Only methods that are in the same class as the method in question.
-
Internal methods can be only be called using reflection.
-
Classes within the same assembly, and classes derived from the declaring class.
5) What is boxing?
a) Encapsulating an object in a value type.
b) Encapsulating a copy of an object in a value type.
c) Encapsulating a value type in an object.
d) Encapsulating a copy of a value type in an object.
6) What compiler switch creates an xml file from the xml comments in the files in an assembly?
-
/text
-
/doc
-
/xml
-
/help
7) What is a satellite Assembly?
-
A peripheral assembly designed to monitor permissions requests from an application.
-
Any DLL file used by an EXE file.
-
An assembly containing localized resources for another assembly.
-
An assembly designed to alter the appearance or ?skin? of an application.
What is a delegate?
-
A strongly typed function pointer.
-
A light weight thread or process that can call a single method.
-
A reference to an object in a different process.
-
An inter-process message channel.
9) How does assembly versioning in .NET prevent DLL Hell?
-
The runtime checks to see that only one version of an assembly is on the machine at any one time.
-
.NET allows assemblies to specify the name AND the version of any assemblies they need to run.
-
The compiler offers compile time checking for backward compatibility.
-
It doesn?t.
10) Which ?Gang of Four? design pattern is shown below?
public class A {
private A instance;
private A() {
}
public
static A Instance {get
{
if ( A == null )
A = new A();
return instance;
}
}
}
-
Factory
-
Abstract Factory
-
Singleton
-
Builder
