Part1 - Tutorials EU

Question 1

What is a class?

Answer 1

A class is a template to create an object. It contains properties as well as methods.

Question 2

What are the key concepts of object-oriented programming?

Answer 2

ncapsulation, abstraction, polymorphism, and inheritance are the main concepts of object-oriented programming.

Question 3

Explain Encapsulation

Answer 3

Encapsulation is a process of wrapping function and data members together in a class. It is like a capsule, a single unit.

Encapsulation is to prevent the unauthorized or unwanted change of data from outside of the function.

For example, we define the properties of class as private. This prevents form direct access of provate members. But we can provide a way to set and get using getters or setters.

Question 4

What is a constructor, and what are its different types?

Answer 4

A constructor is like a method with the same name as the class, but it is a unique method. Even if it is not created, the compiler creates a default constructor in memory at the time of creating an object of the class.

The constructor is used to initialize the object with some default values.
Default constructor, parameterized constructor, copy constructor, static constructor, private constructor are different constructor types.

Question 5

What is a private constructor?

Answer 5

Private Constructor prevents the creation of classes. It also prevents the inhertance of the class.

Usually used in the Singleton pattern where constructor is a private and we will define a public method getInstance(). In this method if instance is not created we will create and return it.

Question 6

What is a destructor in C#?

Answer 6

The Destructor clears out the memory to free up resources. It is managed automatically by the garbage collector. System.GC.collect() is called internally for this purpose. However, if required, it can be done explicitly using a destructor.

Question 7

Is C# code managed or unmanaged code?

Answer 7

C# is managed code because Common language runtime compiles the code to Intermediate language.

Question 8

What are value types and reference types?

Answer 8

We can categorize variables into value type and reference type.

Variables of value type contain the value directly while the variable of a reference type contains the reference of the memory address where the value is stored actually in the memory.

For example bool, byte, int, char, and decimal are value type

And String, class, delegates are examples of reference types.

Question 9

What are namespaces, and is that compulsory?

Answer 9

A namespace is a way of organizing classes of the same group or functionality under the same name. We can call it a module. Although it is not compulsory to put class in a namespace.

Question 10

What is an interface?

Answer 10

An interface is another form of an abstract class that has only abstract public methods, and these methods only have the declaration and not the definition. A class implementing the interface must have the implementation of all the methods of the interface.

Question 11

ow to implement multiple interfaces with the same method name in the same class?

Answer 11

if we want to implement multiple interfaces with the same method name, then we cannot directly implement the body of the function. We have to explicitly provide the name of the interface to implement the body of the method. In this way, the compiler decides which interface methods we are referring to, and this resolves the issue.

Question 12

What is the virtual method, and how is it different from the abstract method?

Answer 12

A virtual method must have a default implementation, and We can override this virtual method using the override keyword in the derived class.

The abstract method is without implementation, and it is created inside the abstract class only. In the case of an abstract class, the class derived from the abstract class must have an implementation of that abstract method.

Question 13

What is method overloading and method overriding?

Answer 13

Method overloading is when we have a function with the same name but a different signature.

Method overriding is when we override the virtual method of a base class in the child class using the override keyword.

Both, method overloading and overriding are a type of polymorphism.

Question 14

Can we use “this” with the static class?

Answer 14

No, we cannot use “this” with the static class because we can only use static variables and static methods in the static class.

Question 15

What is the difference between constants and read-only?

Answer 15

Constant variables have to be assigned a value at the time of declaration only, and we cannot change the value of that variable throughout the program.

We can assign the value to the read-only variable at the time of declaration or in a constructor of the same class.

Question 16

What are Abstract class?

Answer 16

AN abstract class is a partially defined parent class.

For example, we have a Customer base class. This base class has a method, applyDiscount. We have two derived class GoldCustomer and SilverCustomer. Without Abstract class, we can use overriding and make the base’s applyCoupon as virtual. But this has a drawback. What if somebody calls it. Hence we can make this as abstract method. WHen we have a abstratc method, the class should be abstract.

Question 17

ARe abstract methods virtual?

Answer 17

Yes

Question 18

Ca n we create an instance of an abstract class?

Answer 18

No

Question 19

Is it compulasary to implement abstract methods?

Answer 19

Yes

Question 20

can we write a logic in interface

Answer 20

No

Question 21

Can we define methods as private in interface?

Answer 21

No

Question 22

Whats the difference between a .NET and C#?

Answer 22

.NET is a framework and C# is a programming language, that’s what interviewer wants to hear.
.NET framework has collection of ready-made libraries. So for example you want List, Dictionary it has
“System.collections.dll” , you want to make HTTP calls it has “System.Net.Http.dll” and so on.
While C# is programming language it has syntax, grammar, it has those “for loops”,” IF” conditions and so
on.
C# language invokes / orchestrates .NET framework libraries to create an application.

Question 23

What is an interface?

Answer 23

Interface is a contract and by having a contract we have better control on change management and breaking things.

Interfaces support multiple inheritance and this helps to add new methods without affecting the old interface.

Question 24

Can we create instance of an interfaces?

Answer 24

No

Question 25

can we do multiple inheritace with abstract classes?

Answer 25

No

Question 26

If I want to change the interfaces what is the best practice?

Answer 26

Multiple inheirtance

Question 27

WHy do we need construcitr?

Answer 27

COnstructor is a special class which gets automatically invoked when a instance of a class is created.

Question 28

In parent child whihc construcor fires first

Answer 28

First the base constructor is called then the derived construcotr is called.

Question 29

How are initializers executed?

Answer 29

First the derived then base

Question 30

How are static constructors are executed?

Answer 30

First static derived ctor -> static base ctor-> base ctor-> derived ctor.

Question 31

Can we overlaod stayic methods?

Answer 31

yes

Question 32

can we override static?

Answer 32

NO

Question 33

What are static class?

Answer 33

A static class can only contain static data members, static methods, and a static constructor.
It is not allowed to CREATE OBJECTS of the static class.
Static classes are SEALED, means one cannot inherit a static class from another class.
A static class is declared with the help of STATIC keyword.

Question 34

What is difference between ref and out?

Answer 34

Ref and out pass by ref.

Out only from callee to caller. Out needs to be initialized in caller function.

ref value retains in the caller function.

Question 35

What is shadowing or method hiding?

Answer 35

The child class methods will be hidden form the parent class.

  public class baseClass
    {
        public virtual void print()
        {
            Console.WriteLine("Base class");
        }
    }

    public class derivedClass : baseClass
    {
        public void print()
        {
            Console.WriteLine("Derived class");
        }
    }

baseClass b = new derivedClass();

        b.print();

            derivedClass d = new derivedClass();
            d.print();

Question 36

What is a sealed class?

Answer 36

Class which cannot be inheirted

Question 37

Can we create an object of a sealed class?

Answer 37

Yes

Question 38

What is nested class?

Answer 38

A class inside a class

Question 39

Uses of nested class?

Answer 39

Logically group classes. The class we are nesting is only useful inside an enclosing class.

Question 40

Can nested class access the vaiableds of outer class?

Answer 40

No! but we can pass the instanse and use it.

Question 41

can a nested class use any access modifiers?

Answer 41

Yes. To hide use private.

Question 42

What are partial class?

Answer 42

Partial classes can be written in many physical files and while compiling it compiles into one file.

Question 43

What are extension methods?

Answer 43

If we have to extend the existing class methods, then we use extension methods.

To create an extension method,
Create a static class
Inside this static class, create a static method. This method is an extension method. 
The extension method should take class name that is extending as it's first parameter. But we should also pass "this " along with the class name.

Question 44

What is nullable?

Answer 44

Data types in C# are of two types: Value Type and Reference Type; Value types cannot have Null values, but for reference types can have null value.

However, sometime we need to have null values for value types. For example, we may have a class and this class maps to a table in the database. When we map a class to the database, each property of a class will be a column in the table. And a field in the table can be NULL. But if C# does not allow values to be NULL, then we will end up having default values in the fields of the database instead of NULL.

Question 45

WHAT IS THE DIFFERENCE BETWEEN VAR AND DYNAMIC IN C#?

Answer 45

VAR - The type of the variable is decided by the compiler at compile time. DYNAMIC - The type of the variable is decided by the compiler at run time.

Question 46

How do you define const?

Answer 46

const float f = 3.14f;

Question 47

WHat is the range of BYTE?

Answer 47

0-255

Question 48

What is checked keyword?

Answer 48

checked
{
   byte number = 255;
number = number+1;
}

Question 49

How do you convert string to any primitive type?

Answer 49

primitiveType.Parse()

or

Convert.ToByte()
ToIn64
ToInt32

Question 50

Types of operators?

Answer 50

Arthmetic operators: + - / * ++ -- %
Cpmparision operators: == !=
Assignment : = += -=
Logical operators: && || !
Bitwise Operators

Question 51

How do you create an array in C#?

Answer 51

int[] nubers = new int[3] { 1 ,2 ,3}

Question 52

What is a verbatim string?

Answer 52

var stringVar = @”C:\PF\mcafee”

Question 53

how to use format?

Answer 53

String.Format(“{0} {1}”, firstName, lastName);

Question 54

array to string?

Answer 54

string.join(“,”, numbers);

Question 55

What are the differences between struct and classes?

Answer 55

Strut are value type. Classes are reference type.

members are public by default. Class members are private by defualt.

Question 56

How to read each character of a string?

Answer 56

var name = “bharath”

foreach(var c in name)

Question 57

how to generate random number?

Answer 57

var rand = new Random()

rand.Next(min,max)