OOPS Interview Question

Interview Questions - OOPS

What is OOPS?

It is a problem-solving technique to think real world in terms of objects which have responsibilities and provide support to other objects.

What is class?

It is a blueprint of objects which have attributes as well as methods.

What is object?

It is a instance of class which have identity, attributes as well as methods.

What are the four main pillars of OOPS?

Abstraction

Abstraction: It is a technique for arranging complexity of computer systems. it shows only the necessary details to the client of an object.

Encapsulation

Encapsulation: It is a process of hiding all the internal details of an object from the outside world.

Polymorphism

Polymorphism means that you can have multiple classes that can be used interchangeably, even though each class implements the same properties or methods in different ways.

Inheritance

Inheritance help us to create a new classes that reuse, extend and modify the behaviour of other class. The class whose are inherited is called base class and the class inherit it is called derived class.

Difference between Abstraction and Encapsulation?

Abstraction
- Abstraction solves the problem at the design level.
- It shows only the necessary details to the client of an object.

Encapsulation
- Encapsulation solves the problem at the implementation level.
- It is a process of hiding all the internal details of an object from the outside world.

What is static and dynamic binding in polymorphism?
what is compile-time and runtime polymorphism?
What is the difference between method overloading and overriding?

Static or early binding is resolved at compile time. Method overloading is an example of static binding.
Dynamic or late or virtual binding is resolved at run time. Method overriding is an example of dynamic binding.
Method Overloading
Creating a multiple methods in a class with same name but different parameters and types is called as method overloading.

Method overriding
Creating the method in a derived class with same name, same parameters and same return type as in base class is called as method overriding.

What is the use of method overloading ? In which case you go with method overloading?

NA

When to Use Override and New Keywords ?

NA

What is shadowing?

NA

What is deep copy and shallow copy?

NA

What are the Types of inheritance in C#

There are many types some of them explain below
Single inheritance: In this type a derived class created from a single base class.

ClassA{

}

ClassB:ClassA{

}

Multi-level inheritance:
In this type a derived class created from an another derived class.

ClassA{}
CassB:ClassA{}
ClassC:ClassB{}

Multiple inheritances:
In this type, a derived class created from many base class. This type of inheritance not supported by C# but to achieve this interface come in picture.

ClassA:AInterface{}
ClassB:BInterface{}
ClassC: AInterface, BInterface{}

Hybrid inheritance:
It is a combination of multilevel and multiple inheritances, again it's not supported by C# but to achieve this you can use Interface.

What is the diamond problem in inheritance?

In case of multiple inheritance, suppose class A has two subclasses B and C, and a class D has two super classes B and C.If a method present in A is overridden by both B and C but not by D then from which class D will inherit that method B or C? This problem is known as diamond problem.

What is the difference between constant and readonly variables?

Constant:
The constant variable must be assigned the value at the time of declaration.
By default constant is static variable so it can be accessed by ClassName.ConstantVariableName
Its value is known at compile time.
Readonly
A readonly field can be assigned the value at the time of declaration or in the constructor.
It's not static variable so it can be accessed by objClassName.ReadonlyVariableName.
Its value can be known at compile time or run time.

What is the purpose of using private static method?

When you call the static method as private then it only can call from within the class in which its defined.

What is the delegate and can single delegate points to multiple events?

Delegate is a callback which is a pointer to function or method. Yes a single delegate can point to multiple events

What is the difference between Abstract and Interface?
When i can use abstract and interface?

Abstract:
1. We can't create an object of abstract class. It is created to act as the base class.
2. We can implement the method in abstract class.
3. Multiple inheritances not supported by abstract class
Interface:
1. It acts as a signature of functionality for the class.
2. We can't implement the method in an interface.
3. It's supported multiple inheritances.

A class can inherit how many interface and abstract class?

A class can inherit only a single abstract class and can inherit interface more than one.

Why a class can inherit only single abstract class?

NA

How many objects you create from a class?

Till heap memory overflows.

Other Questions

Difference between dictionary and hashtable?

Why multiple instance require for class?

How many constructor a class have?

Scenario Questions

In the below program which method will call or it give exception?

class Program
    {
        static void MethodA(long i)
        {
            Console.WriteLine("Method with long para");
        }

        static void MethodA(int i)
        {
            Console.WriteLine("Method with int para");
        }

        static void Main(string[] args)
        {
            MethodA(10);
        }
    }

The int version of MethodA is being called because 10 is an int literal and the compiler will look for the method which closest matches the input variable(s). To call the long version, you'll need to specify a long literal like so: MethodA(10L);

In the below program which method will call or it give exception?

class Program
    {
        static void MethodA(long i, int l)
        {
            Console.WriteLine("Method A called with long first");
        }

        static void MethodA(int i, long l)
        {
            Console.WriteLine("Method A called with int first");
        }

        static void Main(string[] args)
        {
            MethodA(10, 10);
        }

    }

It will throw ambiguous exception.