OOP (object oriented programming)What is the class?What do you mean by object?What are the differences between class and object?Can you create an object without using new operator in C#?What is constructor and how many constructors can have one class?Differences between constructor and method of the class? What is default constructor?What is parameterized Constructor in C#?What is private constructor: In what instances you will declare a constructor to be private?What is static constructor, Is it possible to have a static constructor in class. If yes why we need to have a static constructor?Does C# provide copy constructor for an object? How do you call the multiple constructors of a class with single object creation?What is constructor chaining in C#?Can a constructor be called directly from a method?What is constructor overloading and how it’s different than method overloading?What is the difference between constructor overloading and method overloading?Is it possible to overload copy constructor in C#?Can we overload static constructors in C#?Can we overload private constructors in C#?Can we give return type of the constructor in C#?What is the destructor and when it’s called?Is it possible to call constructor and destructor explicitly?What is the Structure and why we need it although we have a class?What are the similarities between Class and Structure?What is the difference between Class and Structure?What is copy structure?What is nested structure?Is it always necessary to create an object of the class?How many different ways to create an object of the class?What are the pros and cons of creating object by new() keyword?What are the pros and cons of delegate object creation to DI container?What are the pros and cons of creating an object by reflection?What are the pros and cons of getting an object from an object pool?What are the pros and cons of creating an object by deserialization?Is it possible to create an object without a class in C#?What is constant?What is static modifier? What are the Static fields and methodsWhat is Static ReadOnly?What are the limitations of static?What is readonly? What’s the difference between constant and read-only?What is this keyword?What is base keyword?What is the difference between this and base keyword?Can “this” keyword be used within static method?What are the accessors?What is the static class? Why we need of static class?If someone wants to create static class then what are the rules for the static class?What are the limitations of using static keyword?What are finalizers in c#?How to create N number of instances of C# class?What are the Nested Classes and why we use them?What are the basic four pillars of OOP?What is the Inheritance and why we need of inheritance?How do you inherit a class into other class in C#?What is the concept of base and derive class?What are the different types of inheritance?We have two classes’ base class and child class. A is the base class and B is the child class, If we create an instance of child class then which class’s constructor called first?Does a derived class can inherit the constructors of its base class?What should we do that if we create an object of child class then the parameterized constructor of base class must be invoked?As we know that base constructor invoked first when we create instance of child class but if we create an instance of child class by parameterized constructor and base class has both default and parameterized constructor then which constructor of the base will be invoked?Can you assign an object of derived class to the variable of base class and if both have the same method name then which will be invoked?Can we create instance of base class and store it to derive class?Can we create derive class object inside base class, and if create instance of child class then what will happen?Can we inherit child class from 2 base classes? if yes then how? If not then why?Does C# support Multiple Inheritance?Why multiple inheritance is not supported in C# and why it’s supported in C++?How is multiple inheritance achieved in C#?What are Access Modifiers? Explain private, public, protected, internal, protected internal access modifiersWhat are the default access modifiers of the class?Why classes cannot be declared as protected?Can we declare private class in namespace?What are the valid access specifier used for the declaration of class at namespace level? If we inherit a class, do the private variables also get inherited?Can you prevent your class from being inherited?Can you prevent your class from being inherited without using sealed keyword?What is abstraction?What is encapsulation?What is the difference between abstraction and encapsulation?What is polymorphism?What is static or compile time polymorphism?What is runtime polymorphism or late binding or dynamic binding?What is method overloading?When and why we should use overload methods?What is inheritance based overloading?What are the advantages of using overloading?Can we overload the method in the same class?What is the execution control flow in overloaded methods?What is method overriding?What s virtual keyword?What are the key points to make the method as overridden?When it is must to override the method?When a derived class can overrides the base class member?Can we declare fields inside the class as virtual?When we treat sub-class method as an overriding method?Can we override private virtual method in c#?Can we override method in the same class?Can we execute parent class method if it is overridden in the child class?If we have virtual in base class and the same method is overridden in child class, by creating instance of child class and assign it to base class, then which of the method will be invoked first.What is the difference between method overloading and method overriding?What is method hiding?Can you access a hidden method in the derived which is declared in the base class?What is the difference between method overriding and method hiding?You have a component with 2 parameters and deployed to client side, now you have changed your method with 3 parameters, how can you deploy this without affecting the client code?What is operator overloading?What is abstract class and why we need of it?What are the rules of abstract classes?What is an abstract method?What is concrete method?When do you use abstract class in C#?When to use the abstract method in C#?

What is constructor and how many constructors can have one class?

A constructor in programming is a special method within a class that is automatically called when an object of that class is created. It's used to initialize the object's attributes and perform any necessary setup operations. Constructors allow you to ensure that an object starts in a valid state with appropriate initial values.

In C#, a constructor is defined using the same name as the class and does not have a return type. Constructors can have parameters that allow you to pass values to initialize the attributes of the object being created.

There can be multiple constructors within a class, each with a different set of parameters. This is known as constructor overloading. Having multiple constructors is useful when you want to provide flexibility in how objects are created and initialized.

For example, consider a class 'Person' with attributes 'Name' and 'Age'. Here's how you might define multiple constructors:

class Person {
    public string Name { get; set; }
    public int Age { get; set; }

    // Default constructor with no parameters
    public Person() {
        Name = "Unknown";
        Age = 0;

    // Constructor with name parameter
    public Person(string name) {
        Name = name;
        Age = 0;

    // Constructor with name and age parameters
    public Person(string name, int age) {
        Name = name;
        Age = age;

In this example, the 'Person' class has three constructors:

  1. Default Constructor: Initializes 'Name' and 'Age' to default values.
  2. Constructor with 'Name' Parameter: Initializes 'Name' with the provided name and sets 'Age' to a default value.
  3. Constructor with 'Name' and 'Age' Parameters: Initializes both 'Name' and 'Age' with provided values.

Having multiple constructors allows you to create Person objects in different ways, based on the parameters you provide.

How many types of constructor?

In object-oriented programming, constructors are special methods used to initialize objects when they are created. Constructors can have different parameters and behaviors, depending on the needs of the class and the objects being instantiated. There are several types of constructors based on their parameters and usage:

  1. Default Constructor:
    • A default constructor is one that takes no parameters.
    • It initializes the object's attributes with default values or performs basic setup.
    • If no constructors are defined in a class, a default constructor is automatically provided by the compiler.
  2. Parameterized Constructor:
    • A parameterized constructor takes one or more parameters.
    • It allows you to pass values when creating an object to initialize its attributes.
    • Parameterized constructors are used to ensure objects are created with specific initial values.
  3. Copy Constructor:
    • A copy constructor is used to create a new object by copying the attributes of an existing object of the same class.
    • It helps create deep copies of objects, ensuring that new objects have their own separate memory space for attributes.
    • Copy constructors are used to prevent unintended sharing of attributes between objects.
  4. Static Constructor (Type Initializer):
    • A static constructor is used to initialize static members of a class.
    • It is executed only once, when the class is accessed for the first time.
    • Static constructors are helpful for performing one-time setup tasks for a class.
  5. Private Constructor:
    • A private constructor is used to restrict the instantiation of a class from outside the class itself.
    • It is often used in classes that provide static methods or serve as utility classes.
    • Private constructors prevent accidental creation of instances and enforce the use of the provided static methods.
  6. Chained Constructor (Constructor Overloading):
    • A class can have multiple constructors with different parameter lists.
    • Chained constructors allow one constructor to call another constructor within the same class.
    • This helps avoid duplicate code when different constructors share some common initialization logic.

It's important to choose the appropriate type of constructor based on the requirements of the class and the objects you're creating. Different constructors provide flexibility and control over how objects are initialized and used within your program.

Few points to remember about constructors:

Here are some important points to remember about constructors in programming:

  1. Name and Signature: Constructors have the same name as the class they belong to. They don't have a return type, not even void.
  2. Initialization: Constructors are used to initialize the object's attributes (fields) to meaningful values or to perform setup tasks when an object is created.
  3. Default Constructor: If no constructors are defined in a class, a default constructor (with no parameters) is automatically provided by the compiler.
  4. Parameterized Constructors: Parameterized constructors allow you to provide specific initial values when creating objects.
  5. Copy Constructors: Copy constructors are used to create new objects by copying the attributes of an existing object of the same class.
  6. Static Constructors: Static constructors are used to initialize static members of a class and are executed only once when the class is accessed for the first time.
  7. Private Constructors: Private constructors prevent external instantiation of a class and are often used in utility classes that provide static methods.
  8. Chained Constructors: Chained constructors (constructor overloading) allow one constructor to call another constructor within the same class, avoiding code duplication.
  9. Object Initialization: Constructors are invoked using the new keyword when an object is instantiated.
  10. Order of Execution: If a class has inheritance, constructors of the base class are executed before the derived class constructors.
  11. Inheritance and Constructors: Constructors are not inherited, but constructors of the base class can be invoked from derived class constructors using the base keyword.
  12. No Explicit Return: Constructors don't have a return type, and you cannot use the return keyword within a constructor.
  13. Access Modifiers: Constructors can have access modifiers like public, private, etc., which determine their visibility and accessibility.
  14. Implicit Invocation: Constructors are invoked automatically when an object is created. You don't call them explicitly in your code.
  15. One-Time Initialization: Use constructors for any one-time setup tasks, such as opening connections or allocating resources.
  16. Initialization Order: Initialization of fields happens before the constructor body is executed.
  17. Initialization with Default Values: If you don't explicitly initialize attributes in constructors, they will be set to their default values (e.g., null for reference types, 0 for numeric types).
  18. Constructor Overloading: You can define multiple constructors in the same class with different parameter lists (constructor overloading).
  19. Exception Handling: Constructors can throw exceptions if necessary, but be cautious as they can affect the creation of objects.
  20. Immutable Objects: Constructors are often used to create immutable objects, where attributes are set only once during object creation.

Remembering these points will help you use constructors effectively to create and initialize objects in your programs.