OOP-Object Orientated Programming

Question 1

What are the benefits of OOP?

Answer 1

Data and functions combined, better modularity, low coupling, easier to re-use and closely modelling to the real-world.

Question 2

What are the four pillars of OOP?

Answer 2

Abstraction, Encapsulation, Inheritance, Polymorphism

Question 3

What is Polymorphism

Answer 3

Polymorphism is the ability of objects of different types to provide a unique interface for different implementations of methods.

Question 4

What is Inheritance?

Answer 4

It is a mechanism where you can derive a from another class for a hierarchy of classes that share a set of attributes and methods.

Question 5

What is Encapsulation?

Answer 5

The idea of restricting access to the methods in the class. Hiding it’s data by using properties {get; set;} or declare fields/variables as private.

Question 6

What is abstraction?

Answer 6

The main goal is to handle complexity by hiding unnecessary details from the user. It achieved with either abstract classes or interfaces

Question 7

What is a struct?

Answer 7

It’s is a user-defined data type that can store multiple related items. Structs are similar to classes used in object oriented programming

Question 8

What is the difference between a struct and class

Answer 8

Structs are value types whereas Classes are reference types.

Question 9

What is a backing field?

Answer 9

Properties use backing fields automatically to get and set. A backing field is therefore implicitly hidden. If you want to put logic in your properties, then you have to explicitly state them beforehand.

Question 10

What is object initialisation?

Answer 10

A way to initialise an object of a class or collection. Object initialisers allow you to assign values to the fields or properties at the time of creating an without invoking a constructor.

Question 11

What does the static keyword mean?

Answer 11

Static means that the particular member belongs to a type itself, rather than to an instance of that type.

Question 12

What is an abstract method? An abstract class?

Answer 12

Abstract classes cannot be instantiated, but they can be subclassed. An abstract method is a method that is declared without an implementation.

Question 13

What is an interface?

Answer 13

An interface is a completely abstract class which can only contain abstract methods and properties.

Question 14

What is a C# property?

Answer 14

A property is a member that provides a flexible mechanism to read, write, or compute the value of a private field.

Question 15

What does a constructor do?

Answer 15

It is used to initialise and set default values for the data member of the new object from a class.

Question 16

What is the difference between method overloading and method overriding?

Answer 16

In method overloading, methods must the have the same name and different signatures. Method overriding it’s the same name and same signature.

Question 17

How does C# support Encapsulation?

Answer 17

Properties, backing fields and methods.

Question 18

What is the difference between a constructor and other methods?

Answer 18

Constructor is used to initialise an object whereas method is used to exhibit the function of an object.

Question 19

What does the virtual keyword mean?

Answer 19

The virtual keyword is used to modify a method, property indexer, or event declaration and allow it to be overly in a derived class.

Question 20

What does the sealed keyword mean?

Answer 20

It restricts classes or methods to be inherited by a subclass

Question 21

What are the 5 solid principles?

Answer 21

Single responsibility principle
Open/Closed principle
Liskov Substitution principle 
Interface Segregation principle
Dependency Inversion principle

Question 22

What are the elements of a class?

Answer 22

Class name, type, fields, properties, methods, access modifiers(public, private, protected).

Question 23

What properties and methods does the object class have?

Answer 23

Equals(),GetHashCode(),GetType(),ToString(), ReferenceEquals().

Question 24

What is the single responsibility principle?

Answer 24

That an object/class should only have one responsibility and that it should be completely encapsulated by the class.

Question 25

What is the open/closed principle?

Answer 25

An entity allows it’s behaviour to be extended but never by modifying it’s source code.

Question 26

What is the Liskov Substitution principle?

Answer 26

That objects should be replaceable by instances of their subtypes and that without affecting the functioning of your system from a client’s point of view.

Question 27

What is the Interface Segregation principle?

Answer 27

Large interfaces need to be split into smaller interface that are more specific.

Question 28

What is Dependency Inversion principle?

Answer 28

High level modules should not depend on low level modules rather both should depend on abstraction. Abstraction should not depend on details; rather detail should depend on abstraction.