C# .NET interview questions

What is Constructor Overloading in C# .net ?

Answer:

In Constructor overloading, n number of constructors can be created for the same class. But the signatures of each constructor should vary. For example

public class Employee 
{
 public Employee() 
 { }
 public Employee(String Name) 
 { }
}

Explain Overloading in C# ?

Answer:

When methods are created with the same name, but with different signature its called overloading. For example, WriteLine method in console class is an example of overloading. In the first instance, it takes one variable. In the second instance, “WriteLine” method takes two variable.

Console.WriteLine(x);
Console.WriteLine("The message is {0}", Message);

Different types of overloading in C# are

• Constructor overloading
• Function overloading
• Operator overloading

Define Property in C# ?

Answer:

Properties are a type of class member, that are exposed to the outside world as a pair of Methods. For example, for the static field Minsalary, we will Create a property as shown below.

private double minimumSalary;
public static double MinSalary
{
 get
 {
   return minimumSalary;
 }
 set
 {
   minimumSalary = value;
 }
}

So when we execute the following lines code

double minSal = Employee.MinSalary;

get Method will get triggered and value in minimumSalary field will be returned. When we execute,

Employee. MinSalary = 3000;

What is Reference Type in C# ?

Answer:

Let us explain this with the help of an example. In the code given below,

Employee emp1;
Employee emp2 = new Employee();
emp1 = emp2;

Here emp2 has an object instance of Employee Class. But emp1 object is set as emp2. What this means is that the object emp2 is referred in emp1, rather than copying emp2 instance into emp1. When a change is made in emp2 object, corresponding changes can be seen in emp1 object. 

Explain Static Members in C# ?

Answer:

If an attribute's value had to be same across all the instances of the same class, the static keyword is used. For example, if the Minimum salary should be set for all employees in the employee class, use the following code.

private static double MinSalary = 30000;

To access a private or public attribute or method in a class, at first an object of the class should be created. Then by using the object instance of that class, attributes or methods can be accessed. To access a static variable, we don't want to create an instance of the class containing the static variable. We can directly refer that static variable as shown below.

double var = Employee.MinSalary ;

What are the Access Modifiers in C# ?

Answer:

Different Access Modifier are - Public, Private, Protected, Internal, Protected Internal

• Public – When a method or attribute is defined as Public, it can be accessed from any code in the project. For example, in the above Class “Employee” getName() and setName() are public.
• Private - When a method or attribute is defined as Private, It can be accessed by any code within the containing class only. For example, in the above Class “Employee” attributes name and salary can be accessed within the Class Employee Only. If an attribute or class is defined without access modifiers, it's default access modifier will be private.
• Protected - When attribute and methods are defined as protected, it can be accessed by any method in the inherited classes and any method within the same class. The protected access modifier cannot be applied to classes and interfaces. Methods and fields in a interface can't be declared protected.
• Internal – If an attribute or method is defined as Internal, access is restricted to classes within the current project assembly.
• Protected Internal – If an attribute or method is defined as Protected Internal, access is restricted to classes within the current project assembly and types derived from the containing class. 

What is an Object?

Answer:

An object is an instance of a class. It contains real values instead of variables. For example, let us create an instance of the class Employee called “John”.

Employee John= new Employee();
Now we can access all the methods in the class “Employee” via object “John” as shown below.
John.setName(“XYZ”); 

What is a class ?

Answer:

A class is the generic definition of what an object is. A Class describes all the attributes of the object, as well as the methods that implement the behavior of the member object. In other words, class is a template of an object. For ease of understanding a class, we will look at an example. In the class Employee given below, Name and Salary are the attributes of the class Person. The Setter and Getter methods are used to store and fetch data from the variable.

public class Employee
{
private String name;
private String Salary;
public String getName()
{
  return name;
}
public void setName(String name)
{
  this.name = name; 
}
public String getSalary ()
{
  return Salary;
}
public void setSalary (String Salary)
{
  this. Salary = Salary;
}
} 

Explain the methods and properties of Thread class in C#?

Answer:

Below are the methods and properties of thread class –

• CurrentCulture
• CurrentThread
• CurrentContext
• IsAlive
• IsThreadPoolThread
• IsBackground
• Priority

List out the states of a thread in C#?

Answer:

Below are the states of thread –

• Unstarted State
• Ready State
• Not Runnable State
• Dead State

What is Thread in C#?

Answer:

Thread is an execution path of a program. Thread is used to define the different or unique flow of control. If our application involves some time consuming processes then it’s better to use Multithreading., which involves multiple threads.

List out the pre defined attributes in C#?

Answer:

Below are the predefined attributes in C# -

• Conditional
• Obsolete
• Attribute Usage

Explain Attributes in C#?

Answer:

• Attributes are used to convey the info for runtime about the behavior of elements like – “methods”, “classes”, “enums” etc.
• Attributes can be used to add metadata like – comments, classes, compiler instruction etc.

What are the collection types can be used in C#?

Answer:

Below are the collection types in C# -

• ArrayList
• Stack
• Queue
• SortedList
• HashTable
• Bit Array

Explain Indexers in C#?

Answer:

Indexers are used for allowing the classes to be indexed like arrays. Indexers will resemble the property structure but only difference is indexer’s accessors will take parameters. For example,

class MyCollection<T>
{
 private T[] myArr = new T[100];
 public T this[int t]
 {
 get
 {
 return myArr[t];
 }
 set
 {
 myArr[t] = value;
 }
 }
}

Which string method is used for concatenation of two strings in c#?

Answer:

“Concat” method of String class is used to concatenate two strings. For example,

string.Concat(firstStr, secStr)

Explain Static constructor in C#?

Answer:

If the constructor is declared as static then it will be invoked only once for all number of instances of a class. Static constructor will initialize the static fields of a class.

class MyClass
{
 public string prop1, prop2;
 public MyClass(string a, string b)
 {
 prop1 = a;
 prop2 = b;
 }
Static MyClass()
 {
 Console.WriteLine(“Static Constr Test”);
 }
 public MyClass(MyClass myobj) // Copy Constructor
 {
 prop1 = myobj.prop1;
 prop2 = myobj.prop2;
 }
}

Explain Copy constructor in C#?

Answer:

If the constructor contains the same class in the constructor parameter then it is called as copy constructor.

class MyClass
{
 public string prop1, prop2;
 public MyClass(string a, string b)
 {
 prop1 = a;
 prop2 = b;
 }
 public MyClass(MyClass myobj) // Copy Constructor
 {
 prop1 = myobj.prop1;
 prop2 = myobj.prop2;
 }
}

Explain the types of unit test cases?

Answer:

Below are the list of unit test case types –

• Positive Test cases
• Negative Test cases
• Exception Test cases

Name the compiler of C#?

Answer:

C# Compiler is – CSC.